Merge pull request #8654 from vespa-engine/revert-8651-revert-8650-revert-8645-jvenstad/fix-config-model-inconsitency

Revert "Revert "Revert "Jvenstad/fix config model inconsitency"""

31 files changed, 293 insertions, 374 deletions

diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java b/configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java
index 481f071a32e..ea7b6a88a9c 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java
@@ -53,7 +53,6 @@ import com.yahoo.vespa.config.server.session.SilentDeployLogger;
 import com.yahoo.vespa.config.server.tenant.Rotations;
 import com.yahoo.vespa.config.server.tenant.Tenant;
 import com.yahoo.vespa.config.server.tenant.TenantRepository;
-import com.yahoo.vespa.curator.Lock;
 import com.yahoo.vespa.orchestrator.Orchestrator;
 
 import java.io.File;
@@ -70,7 +69,6 @@ import java.util.Collection;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
-import java.util.OptionalLong;
 import java.util.Set;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -264,10 +262,8 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
     @Override
     public Optional<Instant> lastDeployTime(ApplicationId application) {
         Tenant tenant = tenantRepository.getTenant(application.tenant());
-        if (tenant == null || ! tenant.getApplicationRepo().exists(application)) return Optional.empty();
-        OptionalLong activeSessionId = tenant.getApplicationRepo().activeSessionOf(application);
-        if ( ! activeSessionId.isPresent()) return Optional.empty();
-        LocalSession activeSession = tenant.getLocalSessionRepo().getSession(activeSessionId.getAsLong());
+        if (tenant == null) return Optional.empty();
+        LocalSession activeSession = getActiveSession(tenant, application);
         if (activeSession == null) return Optional.empty();
         return Optional.of(Instant.ofEpochSecond(activeSession.getCreateTime()));
     }
@@ -300,35 +296,34 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
         if (tenant == null) return false;
 
         TenantApplications tenantApplications = tenant.getApplicationRepo();
-        try (Lock lock = tenantApplications.lock(applicationId)) {
-            if ( ! tenantApplications.exists(applicationId)) return false;
-            // Deleting an application is done by deleting the remote session and waiting
-            // until the config server where the deployment happened picks it up and deletes
-            // the local session
-            long sessionId = tenantApplications.requireActiveSessionOf(applicationId);
-            RemoteSession remoteSession = getRemoteSession(tenant, sessionId);
-            remoteSession.createDeleteTransaction().commit();
-
-            log.log(LogLevel.INFO, TenantRepository.logPre(applicationId) + "Waiting for session " + sessionId + " to be deleted");
-            // TODO: Add support for timeout in request
-            Duration waitTime = Duration.ofSeconds(60);
-            if (localSessionHasBeenDeleted(applicationId, sessionId, waitTime)) {
-                log.log(LogLevel.INFO, TenantRepository.logPre(applicationId) + "Session " + sessionId + " deleted");
-            } else {
-                log.log(LogLevel.ERROR, TenantRepository.logPre(applicationId) + "Session " + sessionId + " was not deleted (waited " + waitTime + ")");
-                return false;
-            }
+        if (!tenantApplications.listApplications().contains(applicationId)) return false;
+
+        // Deleting an application is done by deleting the remote session and waiting
+        // until the config server where the deployment happened picks it up and deletes
+        // the local session
+        long sessionId = tenantApplications.getSessionIdForApplication(applicationId);
+        RemoteSession remoteSession = getRemoteSession(tenant, sessionId);
+        remoteSession.createDeleteTransaction().commit();
+
+        log.log(LogLevel.INFO, TenantRepository.logPre(applicationId) + "Waiting for session " + sessionId + " to be deleted");
+        // TODO: Add support for timeout in request
+        Duration waitTime = Duration.ofSeconds(60);
+        if (localSessionHasBeenDeleted(applicationId, sessionId, waitTime)) {
+            log.log(LogLevel.INFO, TenantRepository.logPre(applicationId) + "Session " + sessionId + " deleted");
+        } else {
+            log.log(LogLevel.ERROR, TenantRepository.logPre(applicationId) + "Session " + sessionId + " was not deleted (waited " + waitTime + ")");
+            return false;
+        }
 
-            NestedTransaction transaction = new NestedTransaction();
-            transaction.add(new Rotations(tenant.getCurator(), tenant.getPath()).delete(applicationId)); // TODO: Not unit tested
-            // (When rotations are updated in zk, we need to redeploy the zone app, on the right config server
-            // this is done asynchronously in application maintenance by the node repository)
-            transaction.add(tenantApplications.createDeleteTransaction(applicationId));
+        NestedTransaction transaction = new NestedTransaction();
+        transaction.add(new Rotations(tenant.getCurator(), tenant.getPath()).delete(applicationId)); // TODO: Not unit tested
+        // (When rotations are updated in zk, we need to redeploy the zone app, on the right config server
+        // this is done asynchronously in application maintenance by the node repository)
+        transaction.add(tenantApplications.deleteApplication(applicationId));
 
-            hostProvisioner.ifPresent(provisioner -> provisioner.remove(transaction, applicationId));
-            transaction.onCommitted(() -> log.log(LogLevel.INFO, "Deleted " + applicationId));
-            transaction.commit();
-        }
+        hostProvisioner.ifPresent(provisioner -> provisioner.remove(transaction, applicationId));
+        transaction.onCommitted(() -> log.log(LogLevel.INFO, "Deleted " + applicationId));
+        transaction.commit();
 
         return true;
     }
@@ -424,7 +419,7 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
 
     Set<ApplicationId> listApplications() {
         return tenantRepository.getAllTenants().stream()
-                .flatMap(tenant -> tenant.getApplicationRepo().activeApplications().stream())
+                .flatMap(tenant -> tenant.getApplicationRepo().listApplications().stream())
                 .collect(Collectors.toSet());
     }
 
@@ -483,7 +478,7 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
         if (applicationRepo == null)
             throw new IllegalArgumentException("Application repo for tenant '" + tenant.getName() + "' not found");
 
-        return applicationRepo.requireActiveSessionOf(applicationId);
+        return applicationRepo.getSessionIdForApplication(applicationId);
     }
 
     public void validateThatRemoteSessionIsNotActive(Tenant tenant, long sessionId) {
@@ -525,7 +520,6 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
 
     public long createSession(ApplicationId applicationId, TimeoutBudget timeoutBudget, File applicationDirectory) {
         Tenant tenant = tenantRepository.getTenant(applicationId.tenant());
-        tenant.getApplicationRepo().createApplication(applicationId);
         LocalSessionRepo localSessionRepo = tenant.getLocalSessionRepo();
         SessionFactory sessionFactory = tenant.getSessionFactory();
         LocalSession session = sessionFactory.createSession(applicationDirectory, applicationId, timeoutBudget);
@@ -566,7 +560,7 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
     }
 
     private List<ApplicationId> activeApplications(TenantName tenantName) {
-        return tenantRepository.getTenant(tenantName).getApplicationRepo().activeApplications();
+        return tenantRepository.getTenant(tenantName).getApplicationRepo().listApplications();
     }
 
     // ---------------- Misc operations ----------------------------------------------------------------
@@ -617,7 +611,7 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
         Optional<ApplicationSet> currentActiveApplicationSet = Optional.empty();
         TenantApplications applicationRepo = tenant.getApplicationRepo();
         try {
-            long currentActiveSessionId = applicationRepo.requireActiveSessionOf(appId);
+            long currentActiveSessionId = applicationRepo.getSessionIdForApplication(appId);
             RemoteSession currentActiveSession = getRemoteSession(tenant, currentActiveSessionId);
             if (currentActiveSession != null) {
                 currentActiveApplicationSet = Optional.ofNullable(currentActiveSession.ensureApplicationLoaded());
@@ -647,7 +641,7 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
 
     private List<ApplicationId> listApplicationIds(Tenant tenant) {
         TenantApplications applicationRepo = tenant.getApplicationRepo();
-        return applicationRepo.activeApplications();
+        return applicationRepo.listApplications();
     }
 
     private void cleanupTempDirectory(File tempDir) {
@@ -659,13 +653,13 @@ public class ApplicationRepository implements com.yahoo.config.provision.Deploye
 
     private LocalSession getExistingSession(Tenant tenant, ApplicationId applicationId) {
         TenantApplications applicationRepo = tenant.getApplicationRepo();
-        return getLocalSession(tenant, applicationRepo.requireActiveSessionOf(applicationId));
+        return getLocalSession(tenant, applicationRepo.getSessionIdForApplication(applicationId));
     }
 
     private LocalSession getActiveSession(Tenant tenant, ApplicationId applicationId) {
         TenantApplications applicationRepo = tenant.getApplicationRepo();
-        if (applicationRepo.activeApplications().contains(applicationId)) {
-            return tenant.getLocalSessionRepo().getSession(applicationRepo.requireActiveSessionOf(applicationId));
+        if (applicationRepo.listApplications().contains(applicationId)) {
+            return tenant.getLocalSessionRepo().getSession(applicationRepo.getSessionIdForApplication(applicationId));
         }
         return null;
     }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java b/configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java
index 81eb4107089..2c4d3d99408 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java
@@ -1,6 +1,7 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.config.server.application;
 
+import com.google.common.collect.ImmutableSet;
 import com.yahoo.concurrent.ThreadFactoryFactory;
 import com.yahoo.config.provision.ApplicationId;
 import com.yahoo.config.provision.TenantName;
@@ -11,32 +12,25 @@ import com.yahoo.transaction.Transaction;
 import com.yahoo.vespa.config.server.ReloadHandler;
 import com.yahoo.vespa.config.server.tenant.TenantRepository;
 import com.yahoo.vespa.curator.Curator;
-import com.yahoo.vespa.curator.Lock;
 import com.yahoo.vespa.curator.transaction.CuratorOperations;
 import com.yahoo.vespa.curator.transaction.CuratorTransaction;
 import org.apache.curator.framework.CuratorFramework;
 import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
 
-import java.time.Duration;
+import java.util.ArrayList;
 import java.util.List;
-import java.util.Map;
-import java.util.OptionalLong;
-import java.util.Set;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.Optional;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.logging.Logger;
-import java.util.stream.Collectors;
 
 /**
  * The applications of a tenant, backed by ZooKeeper.
  *
- * Each application is stored under /config/v2/tenants/&lt;tenant&gt;/applications/&lt;application&gt;,
- * the root contains the currently active session, if any. Locks for synchronising writes to these paths, and changes
- * to the config of this application, are found under /config/v2/tenants/&lt;tenant&gt;/locks/&lt;application&gt;.
+ * Each application is stored as a single node under /config/v2/tenants/&lt;tenant&gt;/applications/&lt;applications&gt;,
+ * named the same as the application id and containing the id of the session storing the content of the application.
  *
  * @author Ulf Lilleengen
- * @author jonmv
  */
 public class TenantApplications {
 
@@ -44,20 +38,17 @@ public class TenantApplications {
 
     private final Curator curator;
     private final Path applicationsPath;
-    private final Path locksPath;
     // One thread pool for all instances of this class
     private static final ExecutorService pathChildrenExecutor =
             Executors.newCachedThreadPool(ThreadFactoryFactory.getDaemonThreadFactory(TenantApplications.class.getName()));
     private final Curator.DirectoryCache directoryCache;
     private final ReloadHandler reloadHandler;
     private final TenantName tenant;
-    private final Map<ApplicationId, Lock> locks;
 
-    private TenantApplications(Curator curator, ReloadHandler reloadHandler, TenantName tenant) {
+    private TenantApplications(Curator curator, Path applicationsPath, ReloadHandler reloadHandler, TenantName tenant) {
         this.curator = curator;
-        this.applicationsPath = TenantRepository.getApplicationsPath(tenant);
-        this.locksPath = TenantRepository.getLocksPath(tenant);
-        this.locks = new ConcurrentHashMap<>(2);
+        this.applicationsPath = applicationsPath;
+        curator.create(applicationsPath);
         this.reloadHandler = reloadHandler;
         this.tenant = tenant;
         this.directoryCache = curator.createDirectoryCache(applicationsPath.getAbsolute(), false, false, pathChildrenExecutor);
@@ -66,7 +57,11 @@ public class TenantApplications {
     }
 
     public static TenantApplications create(Curator curator, ReloadHandler reloadHandler, TenantName tenant) {
-        return new TenantApplications(curator, reloadHandler, tenant);
+        try {
+            return new TenantApplications(curator, TenantRepository.getApplicationsPath(tenant), reloadHandler, tenant);
+        } catch (Exception e) {
+            throw new RuntimeException(TenantRepository.logPre(tenant) + "Error creating application repo", e);
+        }
     }
 
     /**
@@ -74,103 +69,75 @@ public class TenantApplications {
      *
      * @return a list of {@link ApplicationId}s that are active.
      */
-    public List<ApplicationId> activeApplications() {
-        return curator.getChildren(applicationsPath).stream()
-                      .filter(this::isValid)
-                      .sorted()
-                      .map(ApplicationId::fromSerializedForm)
-                      .filter(id -> activeSessionOf(id).isPresent())
-                      .collect(Collectors.toUnmodifiableList());
-    }
-
-    private boolean isValid(String appNode) { // TODO jvenstad: Remove after it has run once everywhere.
+    public List<ApplicationId> listApplications() {
         try {
-            ApplicationId.fromSerializedForm(appNode);
-            return true;
-        } catch (IllegalArgumentException __) {
-            log.log(LogLevel.INFO, TenantRepository.logPre(tenant) + "Unable to parse application id from '" +
-                    appNode + "'; deleting it as it shouldn't be here.");
-            try {
-                curator.delete(applicationsPath.append(appNode));
+            List<String> appNodes = curator.framework().getChildren().forPath(applicationsPath.getAbsolute());
+            List<ApplicationId> applicationIds = new ArrayList<>();
+            for (String appNode : appNodes) {
+                parseApplication(appNode).ifPresent(applicationIds::add);
             }
-            catch (RuntimeException e) {
-                log.log(LogLevel.WARNING, TenantRepository.logPre(tenant) + "Failed to clean up stray node '" + appNode + "'!", e);
-            }
-            return false;
+            return applicationIds;
+        } catch (Exception e) {
+            throw new RuntimeException(TenantRepository.logPre(tenant)+"Unable to list applications", e);
         }
     }
 
-    public boolean exists(ApplicationId id) {
-        return curator.exists(applicationPath(id));
-    }
-
-    /** Returns the id of the currently active session for the given application, if any. Throws on unknown applications. */
-    public OptionalLong activeSessionOf(ApplicationId id) {
-        String data = curator.getData(applicationPath(id)).map(Utf8::toString)
-                             .orElseThrow(() -> new IllegalArgumentException("Unknown application '" + id + "'."));
-        return data.isEmpty() ? OptionalLong.empty() : OptionalLong.of(Long.parseLong(data));
+    private Optional<ApplicationId> parseApplication(String appNode) {
+        try {
+            return Optional.of(ApplicationId.fromSerializedForm(appNode));
+        } catch (IllegalArgumentException e) {
+            log.log(LogLevel.INFO, TenantRepository.logPre(tenant)+"Unable to parse application with id '" + appNode + "', ignoring.");
+            return Optional.empty();
+        }
     }
 
     /**
-     * Returns a transaction which writes the given session id as the currently active for the given application.
+     * Register active application and adds it to the repo. If it already exists it is overwritten.
      *
      * @param applicationId An {@link ApplicationId} that represents an active application.
      * @param sessionId Id of the session containing the application package for this id.
      */
-    public Transaction createPutTransaction(ApplicationId applicationId, long sessionId) {
-        return new CuratorTransaction(curator).add(CuratorOperations.setData(applicationPath(applicationId).getAbsolute(), Utf8.toAsciiBytes(sessionId)));
-    }
-
-    /**
-     * Creates a node for the given application, marking its existence.
-     */
-    public void createApplication(ApplicationId id) {
-        try (Lock lock = lock(id)) {
-            curator.create(applicationPath(id));
+    public Transaction createPutApplicationTransaction(ApplicationId applicationId, long sessionId) {
+        if (listApplications().contains(applicationId)) {
+            return new CuratorTransaction(curator).add(CuratorOperations.setData(applicationsPath.append(applicationId.serializedForm()).getAbsolute(), Utf8.toAsciiBytes(sessionId)));
+        } else {
+            return new CuratorTransaction(curator).add(CuratorOperations.create(applicationsPath.append(applicationId.serializedForm()).getAbsolute(), Utf8.toAsciiBytes(sessionId)));
         }
     }
 
     /**
-     * Return the active session id for a given application.
+     * Return the stored session id for a given application.
      *
      * @param  applicationId an {@link ApplicationId}
      * @return session id of given application id.
-     * @throws IllegalArgumentException if the application has no active session
-     */
-    public long requireActiveSessionOf(ApplicationId applicationId) {
-        return activeSessionOf(applicationId)
-                .orElseThrow(() -> new IllegalArgumentException("Application '" + applicationId + "' has no active session."));
-    }
-
-    /**
-     * Returns a transaction which deletes this application.
+     * @throws IllegalArgumentException if the application does not exist
      */
-    public CuratorTransaction createDeleteTransaction(ApplicationId applicationId) {
-        return CuratorTransaction.from(CuratorOperations.deleteAll(applicationPath(applicationId).getAbsolute(), curator), curator);
+    public long getSessionIdForApplication(ApplicationId applicationId) {
+        String path = applicationsPath.append(applicationId.serializedForm()).getAbsolute();
+        try {
+            return Long.parseLong(Utf8.toString(curator.framework().getData().forPath(path)));
+        } catch (Exception e) {
+            throw new IllegalArgumentException(TenantRepository.logPre(applicationId) + "Unable to read the session id from '" + path + "'", e);
+        }
     }
 
     /**
-     * Removes all applications not known to this from the config server state.
+     * Returns a transaction which deletes this application
+     *
+     * @param applicationId an {@link ApplicationId} to delete.
      */
-    public void removeUnusedApplications() {
-        reloadHandler.removeApplicationsExcept(Set.copyOf(activeApplications()));
+    public CuratorTransaction deleteApplication(ApplicationId applicationId) {
+        Path path = applicationsPath.append(applicationId.serializedForm());
+        return CuratorTransaction.from(CuratorOperations.delete(path.getAbsolute()), curator);
     }
 
     /**
-     * Closes the application repo. Once a repo has been closed, it should not be used again.
-     */
+         * Closes the application repo. Once a repo has been closed, it should not be used again.
+         */
     public void close() {
         directoryCache.close();
     }
 
-    /** Returns the lock for changing the session status of the given application. */
-    public Lock lock(ApplicationId id) {
-        curator.create(lockPath(id));
-        Lock lock = locks.computeIfAbsent(id, __ -> new Lock(lockPath(id).getAbsolute(), curator));
-        lock.acquire(Duration.ofMinutes(1)); // These locks shouldn't be held for very long.
-        return lock;
-    }
-
     private void childEvent(CuratorFramework client, PathChildrenCacheEvent event) {
         switch (event.getType()) {
             case CHILD_ADDED:
@@ -200,12 +167,13 @@ public class TenantApplications {
         log.log(LogLevel.DEBUG, TenantRepository.logPre(applicationId) + "Application added: " + applicationId);
     }
 
-    private Path applicationPath(ApplicationId id) {
-        return applicationsPath.append(id.serializedForm());
-    }
-
-    private Path lockPath(ApplicationId id) {
-        return locksPath.append(id.serializedForm());
+    /**
+     * Removes unused applications
+     *
+     */
+    public void removeUnusedApplications() {
+        ImmutableSet<ApplicationId> activeApplications = ImmutableSet.copyOf(listApplications());
+        reloadHandler.removeApplicationsExcept(activeApplications);
     }
 
 }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java b/configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java
index 6d875c529a3..21716730825 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/deploy/Deployment.java
@@ -89,8 +89,9 @@ public class Deployment implements com.yahoo.config.provision.Deployment {
                               timeout, clock, true, true, session.getVespaVersion(), isBootstrap);
     }
 
-    public void setIgnoreSessionStaleFailure(boolean ignoreSessionStaleFailure) {
+    public Deployment setIgnoreSessionStaleFailure(boolean ignoreSessionStaleFailure) {
         this.ignoreSessionStaleFailure = ignoreSessionStaleFailure;
+        return this;
     }
 
     /** Prepares this. This does nothing if this is already prepared */
@@ -115,16 +116,13 @@ public class Deployment implements com.yahoo.config.provision.Deployment {
     /** Activates this. If it is not already prepared, this will call prepare first. */
     @Override
     public void activate() {
-        if ( ! prepared)
+        if (! prepared)
             prepare();
 
         TimeoutBudget timeoutBudget = new TimeoutBudget(clock, timeout);
-
-        try (Lock lock = tenant.getApplicationRepo().lock(session.getApplicationId())) {
-            if ( ! tenant.getApplicationRepo().exists(session.getApplicationId()))
-                return; // Application was deleted.
-
-            validateSessionStatus(session);
+        long sessionId = session.getSessionId();
+        validateSessionStatus(session);
+        try (Lock lock = tenant.getSessionLock(timeout)) {
             NestedTransaction transaction = new NestedTransaction();
             transaction.add(deactivateCurrentActivateNew(applicationRepository.getActiveSession(session.getApplicationId()), session, ignoreSessionStaleFailure));
 
@@ -132,15 +130,13 @@ public class Deployment implements com.yahoo.config.provision.Deployment {
                 hostProvisioner.get().activate(transaction, session.getApplicationId(), session.getAllocatedHosts().getHosts());
             }
             transaction.commit();
+            session.waitUntilActivated(timeoutBudget);
         } catch (RuntimeException e) {
             throw e;
         } catch (Exception e) {
             throw new InternalServerException("Error activating application", e);
         }
-
-        session.waitUntilActivated(timeoutBudget);
-
-        log.log(LogLevel.INFO, session.logPre() + "Session " + session.getSessionId() +
+        log.log(LogLevel.INFO, session.logPre() + "Session " + sessionId + 
                                " activated successfully using " +
                                ( hostProvisioner.isPresent() ? hostProvisioner.get() : "no host provisioner" ) +
                                ". Config generation " + session.getMetaData().getGeneration());
@@ -158,7 +154,7 @@ public class Deployment implements com.yahoo.config.provision.Deployment {
 
     /** Exposes the session of this for testing only */
     public LocalSession session() { return session; }
-
+    
     private long validateSessionStatus(LocalSession localSession) {
         long sessionId = localSession.getSessionId();
         if (Session.Status.NEW.equals(localSession.getStatus())) {
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/host/HostRegistry.java b/configserver/src/main/java/com/yahoo/vespa/config/server/host/HostRegistry.java
index a7f8b8164a5..77572856ff5 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/host/HostRegistry.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/host/HostRegistry.java
@@ -36,7 +36,6 @@ public class HostRegistry<T> implements HostValidator<T> {
         addHosts(key, newHosts);
     }
 
-    @Override
     public synchronized void verifyHosts(T key, Collection<String> newHosts) {
         for (String host : newHosts) {
             if (hostAlreadyTaken(host, key)) {
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandler.java b/configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandler.java
index cdf995b80bb..6345532d4ff 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandler.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandler.java
@@ -56,7 +56,7 @@ public class ListApplicationsHandler extends HttpHandler {
         Utils.checkThatTenantExists(tenantRepository, tenantName);
         Tenant tenant = tenantRepository.getTenant(tenantName);
         TenantApplications applicationRepo = tenant.getApplicationRepo();
-        return applicationRepo.activeApplications();
+        return applicationRepo.listApplications();
     }
 
     private static String createUrlStringFromId(String urlBase, ApplicationId id, Zone zone) {
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/LocalSession.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/LocalSession.java
index af8956803ab..0f9f8b72de1 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/LocalSession.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/LocalSession.java
@@ -83,6 +83,12 @@ public class LocalSession extends Session implements Comparable<LocalSession> {
         setStatus(Session.Status.PREPARE);
     }
 
+    private Transaction setActive() {
+        Transaction transaction = createSetStatusTransaction(Status.ACTIVATE);
+        transaction.add(applicationRepo.createPutApplicationTransaction(zooKeeperClient.readApplicationId(), getSessionId()).operations());
+        return transaction;
+    }
+
     private Transaction createSetStatusTransaction(Status status) {
         return zooKeeperClient.createWriteStatusTransaction(status);
     }
@@ -93,10 +99,8 @@ public class LocalSession extends Session implements Comparable<LocalSession> {
 
     public Transaction createActivateTransaction() {
         zooKeeperClient.createActiveWaiter();
-        superModelGenerationCounter.increment(); // TODO jvenstad: I hope this counter isn't used for serious things, as it's updated way ahead of activation.
-        Transaction transaction = createSetStatusTransaction(Status.ACTIVATE);
-        transaction.add(applicationRepo.createPutTransaction(zooKeeperClient.readApplicationId(), getSessionId()).operations());
-        return transaction;
+        superModelGenerationCounter.increment();
+        return setActive();
     }
 
     public Transaction createDeactivateTransaction() {
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSession.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSession.java
index 3f1619882cd..172d9c025d5 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSession.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSession.java
@@ -5,8 +5,8 @@ import com.yahoo.config.application.api.ApplicationPackage;
 import com.yahoo.config.provision.AllocatedHosts;
 import com.yahoo.config.provision.TenantName;
 import com.yahoo.lang.SettableOptional;
-import com.yahoo.log.LogLevel;
 import com.yahoo.transaction.Transaction;
+import com.yahoo.log.LogLevel;
 import com.yahoo.vespa.config.server.GlobalComponentRegistry;
 import com.yahoo.vespa.config.server.ReloadHandler;
 import com.yahoo.vespa.config.server.application.ApplicationSet;
@@ -29,7 +29,7 @@ import java.util.logging.Logger;
 public class RemoteSession extends Session {
 
     private static final Logger log = Logger.getLogger(RemoteSession.class.getName());
-    private ApplicationSet applicationSet = null;
+    private volatile ApplicationSet applicationSet = null;
     private final ActivatedModelsBuilder applicationLoader;
     private final Clock clock;
 
@@ -69,15 +69,18 @@ public class RemoteSession extends Session {
                                                                      clock.instant()));
     }
 
-    public synchronized ApplicationSet ensureApplicationLoaded() {
-        return applicationSet == null ? applicationSet = loadApplication() : applicationSet;
+    public ApplicationSet ensureApplicationLoaded() {
+        if (applicationSet == null) {
+            applicationSet = loadApplication();
+        }
+        return applicationSet;
     }
 
     public Session.Status getStatus() {
         return zooKeeperClient.readStatus();
     }
 
-    public synchronized void deactivate() {
+    public void deactivate() {
         applicationSet = null;
     }
 
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSessionRepo.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSessionRepo.java
index bbb06515bef..15182813a22 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSessionRepo.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/RemoteSessionRepo.java
@@ -1,36 +1,33 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.config.server.session;
 
+import java.time.Duration;
+import java.time.Instant;
+import java.util.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.stream.Collectors;
+
 import com.google.common.collect.HashMultiset;
 import com.google.common.collect.Multiset;
 import com.yahoo.concurrent.ThreadFactoryFactory;
-import com.yahoo.config.provision.ApplicationId;
 import com.yahoo.config.provision.TenantName;
 import com.yahoo.log.LogLevel;
 import com.yahoo.path.Path;
-import com.yahoo.vespa.config.server.ReloadHandler;
+import com.yahoo.vespa.config.server.application.ApplicationSet;
 import com.yahoo.vespa.config.server.application.TenantApplications;
-import com.yahoo.vespa.config.server.monitoring.MetricUpdater;
 import com.yahoo.vespa.config.server.tenant.TenantRepository;
-import com.yahoo.vespa.config.server.zookeeper.ConfigCurator;
 import com.yahoo.vespa.curator.Curator;
 import com.yahoo.yolean.Exceptions;
-import org.apache.curator.framework.CuratorFramework;
-import org.apache.curator.framework.recipes.cache.ChildData;
-import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
+import com.yahoo.vespa.config.server.ReloadHandler;
+import com.yahoo.config.provision.ApplicationId;
+import com.yahoo.vespa.config.server.monitoring.MetricUpdater;
+import com.yahoo.vespa.config.server.zookeeper.ConfigCurator;
 
-import java.time.Duration;
-import java.time.Instant;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
-import java.util.logging.Level;
-import java.util.logging.Logger;
-import java.util.stream.Collectors;
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.cache.*;
 
 /**
  * Will watch/prepare sessions (applications) based on watched nodes in ZooKeeper, set for example
@@ -118,6 +115,19 @@ public class RemoteSessionRepo extends SessionRepo<RemoteSession> {
         return (created.plus(expiryTime).isBefore(Instant.now()));
     }
 
+    private void loadActiveSession(RemoteSession session) {
+        tryReload(session.ensureApplicationLoaded(), session.logPre());
+    }
+
+    private void tryReload(ApplicationSet applicationSet, String logPre) {
+        try {
+            reloadHandler.reloadConfig(applicationSet);
+            log.log(LogLevel.INFO, logPre + "Application activated successfully: " + applicationSet.getId());
+        } catch (Exception e) {
+            log.log(LogLevel.WARNING, logPre + "Skipping loading of application '" + applicationSet.getId() + "': " + Exceptions.toMessageString(e));
+        }
+    }
+
     private List<Long> getSessionListFromDirectoryCache(List<ChildData> children) {
         return getSessionList(children.stream()
                                       .map(child -> Path.fromString(child.getPath()).getName())
@@ -180,16 +190,15 @@ public class RemoteSessionRepo extends SessionRepo<RemoteSession> {
     }
 
     private void loadSessionIfActive(RemoteSession session) {
-        for (ApplicationId applicationId : applicationRepo.activeApplications()) {
+        for (ApplicationId applicationId : applicationRepo.listApplications()) {
             try {
-                if (applicationRepo.requireActiveSessionOf(applicationId) == session.getSessionId()) {
+                if (applicationRepo.getSessionIdForApplication(applicationId) == session.getSessionId()) {
                     log.log(LogLevel.DEBUG, "Found active application for session " + session.getSessionId() + " , loading it");
-                    reloadHandler.reloadConfig(session.ensureApplicationLoaded());
-                    log.log(LogLevel.INFO, session.logPre() + "Application activated successfully: " + applicationId);
-                    return;
+                    loadActiveSession(session);
+                    break;
                 }
             } catch (Exception e) {
-                log.log(LogLevel.WARNING, session.logPre() + "Skipping loading of application '" + applicationId + "': " + Exceptions.toMessageString(e));
+                log.log(LogLevel.WARNING, session.logPre() + " error reading session id for " + applicationId, e);
             }
         }
     }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactory.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactory.java
index 5527d3060f7..a3dea83d50c 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactory.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactory.java
@@ -17,6 +17,8 @@ public interface SessionFactory {
     /**
      * Creates a new deployment session from an application package.
      *
+     *
+     *
      * @param applicationDirectory a File pointing to an application.
      * @param applicationId application id for this new session.
      * @param timeoutBudget Timeout for creating session and waiting for other servers.
@@ -27,10 +29,10 @@ public interface SessionFactory {
     /**
      * Creates a new deployment session from an already existing session.
      *
-     * @param existingSession the session to use as base
+     * @param existingSession The session to use as base
      * @param logger a deploy logger where the deploy log will be written.
-     * @param internalRedeploy whether this session is for a system internal redeploy — not an application package change
-     * @param timeoutBudget timeout for creating session and waiting for other servers.
+     * @param internalRedeploy if this session is for a system internal redeploy not an application package change
+     * @param timeoutBudget Timeout for creating session and waiting for other servers.
      * @return a new session
      */
     LocalSession createSessionFromExisting(LocalSession existingSession, DeployLogger logger,
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactoryImpl.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactoryImpl.java
index d8ba5890545..b79ea720aea 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactoryImpl.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionFactoryImpl.java
@@ -188,11 +188,10 @@ public class SessionFactoryImpl implements SessionFactory, LocalSessionLoader {
     }
 
     private long getActiveSessionId(ApplicationId applicationId) {
-        List<ApplicationId> applicationIds = applicationRepo.activeApplications();
+        List<ApplicationId> applicationIds = applicationRepo.listApplications();
         if (applicationIds.contains(applicationId)) {
-            return applicationRepo.requireActiveSessionOf(applicationId);
+            return applicationRepo.getSessionIdForApplication(applicationId);
         }
         return nonExistingActiveSession;
     }
-
 }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionPreparer.java b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionPreparer.java
index f0ceeb186fe..43a5ff6d0c2 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionPreparer.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionPreparer.java
@@ -113,8 +113,9 @@ public class SessionPreparer {
             log.log(LogLevel.DEBUG, () -> "time used " + params.getTimeoutBudget().timesUsed() +
                     " : " + params.getApplicationId());
             return preparation.result();
-        }
-        catch (IllegalArgumentException e) {
+        } catch (OutOfCapacityException e) {
+            throw e;
+        } catch (IllegalArgumentException e) {
             throw new InvalidApplicationException("Invalid application package", e);
         }
     }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/Tenant.java b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/Tenant.java
index 88e71d7ddd1..a68f4a396cd 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/Tenant.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/Tenant.java
@@ -11,8 +11,10 @@ import com.yahoo.vespa.config.server.session.LocalSessionRepo;
 import com.yahoo.vespa.config.server.session.RemoteSessionRepo;
 import com.yahoo.vespa.config.server.session.SessionFactory;
 import com.yahoo.vespa.curator.Curator;
+import com.yahoo.vespa.curator.Lock;
 import org.apache.zookeeper.data.Stat;
 
+import java.time.Duration;
 import java.time.Instant;
 import java.util.Optional;
 
@@ -28,7 +30,7 @@ public class Tenant implements TenantHandlerProvider {
 
     static final String SESSIONS = "sessions";
     static final String APPLICATIONS = "applications";
-    static final String LOCKS = "locks";
+    static final String SESSION_LOCK_PATH = "activateLock";
 
     private final TenantName name;
     private final RemoteSessionRepo remoteSessionRepo;
@@ -36,6 +38,7 @@ public class Tenant implements TenantHandlerProvider {
     private final SessionFactory sessionFactory;
     private final LocalSessionRepo localSessionRepo;
     private final TenantApplications applicationRepo;
+    private final Lock sessionLock;
     private final RequestHandler requestHandler;
     private final ReloadHandler reloadHandler;
     private final TenantFileSystemDirs tenantFileSystemDirs;
@@ -58,6 +61,7 @@ public class Tenant implements TenantHandlerProvider {
         this.remoteSessionRepo = remoteSessionRepo;
         this.sessionFactory = sessionFactory;
         this.localSessionRepo = localSessionRepo;
+        this.sessionLock = createLock(curator, path);
         this.applicationRepo = applicationRepo;
         this.tenantFileSystemDirs = tenantFileSystemDirs;
         this.curator = curator;
@@ -106,6 +110,14 @@ public class Tenant implements TenantHandlerProvider {
         return localSessionRepo;
     }
 
+    /**
+     * This lock allows activation and deactivation of sessions under this tenant.
+     */
+    public Lock getSessionLock(Duration timeout) {
+        sessionLock.acquire(timeout);
+        return sessionLock;
+    }
+    
     @Override
     public String toString() {
         return getName().value();
@@ -153,4 +165,10 @@ public class Tenant implements TenantHandlerProvider {
         curator.delete(path);
     }
 
+    private static Lock createLock(Curator curator, Path tenantPath) {
+        Path lockPath = tenantPath.append(SESSION_LOCK_PATH);
+        curator.create(lockPath);
+        return new Lock(lockPath.getAbsolute(), curator);
+    }
+
 }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantBuilder.java b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantBuilder.java
index 943ae6248fc..078b6e861a9 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantBuilder.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantBuilder.java
@@ -31,7 +31,7 @@ public class TenantBuilder {
     private SessionFactory sessionFactory;
     private LocalSessionLoader localSessionLoader;
     private TenantApplications applicationRepo;
-    private TenantRequestHandler reloadHandler;
+    private ReloadHandler reloadHandler;
     private RequestHandler requestHandler;
     private RemoteSessionFactory remoteSessionFactory;
     private TenantFileSystemDirs tenantFileSystemDirs;
@@ -120,7 +120,7 @@ public class TenantBuilder {
 
     private void createApplicationRepo() {
         if (applicationRepo == null) {
-            applicationRepo = reloadHandler.applications();
+            applicationRepo = TenantApplications.create(componentRegistry.getCurator(), reloadHandler, tenant);
         }
     }
 
@@ -130,8 +130,7 @@ public class TenantBuilder {
                                                                  tenant,
                                                                  Collections.singletonList(componentRegistry.getReloadListener()),
                                                                  ConfigResponseFactory.create(componentRegistry.getConfigserverConfig()),
-                                                                 componentRegistry.getHostRegistries(),
-                                                                 componentRegistry.getCurator());
+                                                                 componentRegistry.getHostRegistries());
             if (hostValidator == null) {
                 this.hostValidator = impl;
             }
@@ -165,5 +164,9 @@ public class TenantBuilder {
         }
     }
 
+    public TenantApplications getApplicationRepo() {
+        return applicationRepo;
+    }
+
     public TenantName getTenantName() { return tenant; }
 }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRepository.java b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRepository.java
index c37db0e0df5..9c74c9c1e67 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRepository.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRepository.java
@@ -262,10 +262,7 @@ public class TenantRepository {
      */
     private synchronized void writeTenantPath(TenantName name) {
         Path tenantPath = getTenantPath(name);
-        curator.createAtomically(tenantPath,
-                                 tenantPath.append(Tenant.SESSIONS),
-                                 tenantPath.append(Tenant.APPLICATIONS),
-                                 tenantPath.append(Tenant.LOCKS));
+        curator.createAtomically(tenantPath, tenantPath.append(Tenant.SESSIONS), tenantPath.append(Tenant.APPLICATIONS));
     }
 
     /**
@@ -409,11 +406,4 @@ public class TenantRepository {
         return getTenantPath(tenantName).append(Tenant.APPLICATIONS);
     }
 
-    /**
-     * Gets zookeeper path for locks for a tenant's applications
-     */
-    public static Path getLocksPath(TenantName tenantName) {
-        return getTenantPath(tenantName).append(Tenant.LOCKS);
-    }
-
 }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandler.java b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandler.java
index 3f2b8c76e44..a341061bd9a 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandler.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandler.java
@@ -6,7 +6,6 @@ import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Optional;
-import java.util.OptionalLong;
 import java.util.Set;
 
 import com.yahoo.component.Version;
@@ -17,7 +16,6 @@ import com.yahoo.vespa.config.protocol.ConfigResponse;
 import com.yahoo.vespa.config.server.NotFoundException;
 import com.yahoo.vespa.config.server.application.ApplicationMapper;
 import com.yahoo.vespa.config.server.application.ApplicationSet;
-import com.yahoo.vespa.config.server.application.TenantApplications;
 import com.yahoo.vespa.config.server.rpc.ConfigResponseFactory;
 import com.yahoo.vespa.config.server.host.HostRegistries;
 import com.yahoo.vespa.config.server.host.HostRegistry;
@@ -31,8 +29,6 @@ import com.yahoo.config.provision.ApplicationId;
 import com.yahoo.config.provision.TenantName;
 import com.yahoo.vespa.config.server.monitoring.MetricUpdater;
 import com.yahoo.vespa.config.server.monitoring.Metrics;
-import com.yahoo.vespa.curator.Curator;
-import com.yahoo.vespa.curator.Lock;
 
 /**
  * A per tenant request handler, for handling reload (activate application) and getConfig requests for
@@ -48,25 +44,23 @@ public class TenantRequestHandler implements RequestHandler, ReloadHandler, Host
     private final TenantName tenant;
     private final List<ReloadListener> reloadListeners;
     private final ConfigResponseFactory responseFactory;
+
     private final HostRegistry<ApplicationId> hostRegistry;
     private final ApplicationMapper applicationMapper = new ApplicationMapper();
     private final MetricUpdater tenantMetricUpdater;
     private final Clock clock = Clock.systemUTC();
-    private final TenantApplications applications;
 
     public TenantRequestHandler(Metrics metrics,
                                 TenantName tenant,
                                 List<ReloadListener> reloadListeners,
                                 ConfigResponseFactory responseFactory,
-                                HostRegistries hostRegistries,
-                                Curator curator) { // TODO jvenstad: Merge this class with TenantApplications, and straighten this out.
+                                HostRegistries hostRegistries) {
         this.metrics = metrics;
         this.tenant = tenant;
-        this.reloadListeners = List.copyOf(reloadListeners);
+        this.reloadListeners = reloadListeners;
         this.responseFactory = responseFactory;
-        this.tenantMetricUpdater = metrics.getOrCreateMetricUpdater(Metrics.createDimensions(tenant));
-        this.hostRegistry = hostRegistries.createApplicationHostRegistry(tenant);
-        this.applications = TenantApplications.create(curator, this, tenant);
+        tenantMetricUpdater = metrics.getOrCreateMetricUpdater(Metrics.createDimensions(tenant));
+        hostRegistry = hostRegistries.createApplicationHostRegistry(tenant);
     }
 
     /**
@@ -99,40 +93,26 @@ public class TenantRequestHandler implements RequestHandler, ReloadHandler, Host
      *
      * @param applicationSet the {@link ApplicationSet} to be reloaded
      */
-    @Override
     public void reloadConfig(ApplicationSet applicationSet) {
-        ApplicationId id = applicationSet.getId();
-        try (Lock lock = applications.lock(id)) {
-            if ( ! applications.exists(id))
-                return; // Application was deleted before activation.
-            if (applicationSet.getApplicationGeneration() != applications.requireActiveSessionOf(id))
-                return; // Application activated a new session before we got here.
-
-            setLiveApp(applicationSet);
-            notifyReloadListeners(applicationSet);
-        }
+        setLiveApp(applicationSet);
+        notifyReloadListeners(applicationSet);
     }
 
     @Override
     public void removeApplication(ApplicationId applicationId) {
-        try (Lock lock = applications.lock(applicationId)) {
-            if (applications.exists(applicationId))
-                return; // Application was deployed again.
-
-            if (applicationMapper.hasApplication(applicationId, clock.instant())) {
-                applicationMapper.remove(applicationId);
-                hostRegistry.removeHostsForKey(applicationId);
-                reloadListenersOnRemove(applicationId);
-                tenantMetricUpdater.setApplications(applicationMapper.numApplications());
-                metrics.removeMetricUpdater(Metrics.createDimensions(applicationId));
-            }
+        if (applicationMapper.hasApplication(applicationId, clock.instant())) {
+            applicationMapper.remove(applicationId);
+            hostRegistry.removeHostsForKey(applicationId);
+            reloadListenersOnRemove(applicationId);
+            tenantMetricUpdater.setApplications(applicationMapper.numApplications());
+            metrics.removeMetricUpdater(Metrics.createDimensions(applicationId));
         }
     }
 
     @Override
     public void removeApplicationsExcept(Set<ApplicationId> applications) {
         for (ApplicationId activeApplication : applicationMapper.listApplicationIds()) {
-            if ( ! applications.contains(activeApplication)) {
+            if (! applications.contains(activeApplication)) {
                 log.log(LogLevel.INFO, "Will remove deleted application " + activeApplication.toShortString());
                 removeApplication(activeApplication);
             }
@@ -257,6 +237,4 @@ public class TenantRequestHandler implements RequestHandler, ReloadHandler, Host
         }
     }
 
-    TenantApplications applications() { return applications; }
-
 }
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/ApplicationRepositoryTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/ApplicationRepositoryTest.java
index 7a4998215e3..3d94dedf651 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/ApplicationRepositoryTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/ApplicationRepositoryTest.java
@@ -286,7 +286,7 @@ public class ApplicationRepositoryTest {
 
         assertTrue(deployment2.isPresent());
         deployment2.get().activate(); // session 3
-        long activeSessionId = tester.tenant().getApplicationRepo().requireActiveSessionOf(tester.applicationId());
+        long activeSessionId = tester.tenant().getApplicationRepo().getSessionIdForApplication(tester.applicationId());
 
         clock.advance(Duration.ofSeconds(10));
         Optional<com.yahoo.config.provision.Deployment> deployment3 = tester.redeployFromLocalActive();
@@ -296,7 +296,7 @@ public class ApplicationRepositoryTest {
         LocalSession deployment3session = ((com.yahoo.vespa.config.server.deploy.Deployment) deployment3.get()).session();
         assertNotEquals(activeSessionId, deployment3session);
         // No change to active session id
-        assertEquals(activeSessionId, tester.tenant().getApplicationRepo().requireActiveSessionOf(tester.applicationId()));
+        assertEquals(activeSessionId, tester.tenant().getApplicationRepo().getSessionIdForApplication(tester.applicationId()));
         assertEquals(3, tester.tenant().getLocalSessionRepo().listSessions().size());
 
         clock.advance(Duration.ofHours(1)); // longer than session lifetime
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/application/TenantApplicationsTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/application/TenantApplicationsTest.java
index 69c88dc0275..a708e4d8ace 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/application/TenantApplicationsTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/application/TenantApplicationsTest.java
@@ -39,12 +39,12 @@ public class TenantApplicationsTest {
         writeApplicationData(createApplicationId("foo"), 3L);
         writeApplicationData(createApplicationId("bar"), 4L);
         TenantApplications repo = createZKAppRepo();
-        List<ApplicationId> applications = repo.activeApplications();
+        List<ApplicationId> applications = repo.listApplications();
         assertThat(applications.size(), is(2));
-        assertThat(applications.get(0).application().value(), is("bar"));
-        assertThat(applications.get(1).application().value(), is("foo"));
-        assertThat(repo.requireActiveSessionOf(applications.get(0)), is(4L));
-        assertThat(repo.requireActiveSessionOf(applications.get(1)), is(3L));
+        assertThat(applications.get(0).application().value(), is("foo"));
+        assertThat(applications.get(1).application().value(), is("bar"));
+        assertThat(repo.getSessionIdForApplication(applications.get(0)), is(3L));
+        assertThat(repo.getSessionIdForApplication(applications.get(1)), is(4L));
     }
 
     @Test
@@ -52,7 +52,7 @@ public class TenantApplicationsTest {
         writeApplicationData(createApplicationId("foo"), 3L);
         writeApplicationData("invalid", 3L);
         TenantApplications repo = createZKAppRepo();
-        List<ApplicationId> applications = repo.activeApplications();
+        List<ApplicationId> applications = repo.listApplications();
         assertThat(applications.size(), is(1));
         assertThat(applications.get(0).application().value(), is("foo"));
     }
@@ -60,7 +60,7 @@ public class TenantApplicationsTest {
     @Test(expected = IllegalArgumentException.class)
     public void require_that_requesting_session_for_unknown_application_throws_exception() throws Exception {
         TenantApplications repo = createZKAppRepo();
-        repo.requireActiveSessionOf(createApplicationId("nonexistent"));
+        repo.getSessionIdForApplication(createApplicationId("nonexistent"));
     }
 
     @Test(expected = IllegalArgumentException.class)
@@ -70,19 +70,18 @@ public class TenantApplicationsTest {
         curatorFramework.create().creatingParentsIfNeeded()
                 .forPath(TenantRepository.getApplicationsPath(tenantName).append(baz.serializedForm()).getAbsolute());
         TenantApplications repo = createZKAppRepo();
-        repo.requireActiveSessionOf(baz);
+        repo.getSessionIdForApplication(baz);
     }
 
     @Test
     public void require_that_application_ids_can_be_written() throws Exception {
         TenantApplications repo = createZKAppRepo();
         ApplicationId myapp = createApplicationId("myapp");
-        repo.createApplication(myapp);
-        repo.createPutTransaction(myapp, 3l).commit();
+        repo.createPutApplicationTransaction(myapp, 3l).commit();
         String path = TenantRepository.getApplicationsPath(tenantName).append(myapp.serializedForm()).getAbsolute();
         assertTrue(curatorFramework.checkExists().forPath(path) != null);
         assertThat(Utf8.toString(curatorFramework.getData().forPath(path)), is("3"));
-        repo.createPutTransaction(myapp, 5l).commit();
+        repo.createPutApplicationTransaction(myapp, 5l).commit();
         assertTrue(curatorFramework.checkExists().forPath(path) != null);
         assertThat(Utf8.toString(curatorFramework.getData().forPath(path)), is("5"));
     }
@@ -92,15 +91,13 @@ public class TenantApplicationsTest {
         TenantApplications repo = createZKAppRepo();
         ApplicationId id1 = createApplicationId("myapp");
         ApplicationId id2 = createApplicationId("myapp2");
-        repo.createApplication(id1);
-        repo.createApplication(id2);
-        repo.createPutTransaction(id1, 1).commit();
-        repo.createPutTransaction(id2, 1).commit();
-        assertThat(repo.activeApplications().size(), is(2));
-        repo.createDeleteTransaction(id1).commit();
-        assertThat(repo.activeApplications().size(), is(1));
-        repo.createDeleteTransaction(id2).commit();
-        assertThat(repo.activeApplications().size(), is(0));
+        repo.createPutApplicationTransaction(id1, 1).commit();
+        repo.createPutApplicationTransaction(id2, 1).commit();
+        assertThat(repo.listApplications().size(), is(2));
+        repo.deleteApplication(id1).commit();
+        assertThat(repo.listApplications().size(), is(1));
+        repo.deleteApplication(id2).commit();
+        assertThat(repo.listApplications().size(), is(0));
     }
 
     @Test
@@ -111,7 +108,7 @@ public class TenantApplicationsTest {
         MockReloadHandler reloadHandler = new MockReloadHandler();
         TenantApplications repo = createZKAppRepo(reloadHandler);
         assertNull(reloadHandler.lastRemoved);
-        repo.createDeleteTransaction(foo).commit();
+        repo.deleteApplication(foo).commit();
         long endTime = System.currentTimeMillis() + 60_000;
         while (System.currentTimeMillis() < endTime && reloadHandler.lastRemoved == null) {
             Thread.sleep(100);
@@ -129,7 +126,11 @@ public class TenantApplicationsTest {
     }
 
     private static ApplicationId createApplicationId(String name) {
-        return ApplicationId.from(tenantName.value(), name, "myinst");
+        return new ApplicationId.Builder()
+                .tenant(tenantName.value())
+                .applicationName(name)
+                .instanceName("myinst")
+                .build();
     }
 
     private void writeApplicationData(ApplicationId applicationId, long sessionId) throws Exception {
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/deploy/DeployTester.java b/configserver/src/test/java/com/yahoo/vespa/config/server/deploy/DeployTester.java
index 6b67dcc4e9a..7ffb9552cf8 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/deploy/DeployTester.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/deploy/DeployTester.java
@@ -183,7 +183,7 @@ public class DeployTester {
     public AllocatedHosts getAllocatedHostsOf(ApplicationId applicationId) {
         Tenant tenant = tenant();
         LocalSession session = tenant.getLocalSessionRepo().getSession(tenant.getApplicationRepo()
-                                                                             .requireActiveSessionOf(applicationId));
+                                                                             .getSessionIdForApplication(applicationId));
         return session.getAllocatedHosts();
     }
 
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationContentHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationContentHandlerTest.java
index c6a8e1f2f9d..b0bb3bf244f 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationContentHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationContentHandlerTest.java
@@ -56,14 +56,12 @@ public class ApplicationContentHandlerTest extends ContentHandlerTestBase {
         session2 = new MockSession(2l, FilesApplicationPackage.fromFile(new File("src/test/apps/content")));
         Tenant tenant1 = tenantRepository.getTenant(tenantName1);
         tenant1.getLocalSessionRepo().addSession(session2);
-        tenant1.getApplicationRepo().createApplication(idTenant1);
-        tenant1.getApplicationRepo().createPutTransaction(idTenant1, 2l).commit();
+        tenant1.getApplicationRepo().createPutApplicationTransaction(idTenant1, 2l).commit();
 
         MockSession session3 = new MockSession(3l, FilesApplicationPackage.fromFile(new File("src/test/apps/content2")));
         Tenant tenant2 = tenantRepository.getTenant(tenantName2);
         tenant2.getLocalSessionRepo().addSession(session3);
-        tenant2.getApplicationRepo().createApplication(idTenant2);
-        tenant2.getApplicationRepo().createPutTransaction(idTenant2, 3l).commit();
+        tenant2.getApplicationRepo().createPutApplicationTransaction(idTenant2, 3l).commit();
 
         handler = new ApplicationHandler(ApplicationHandler.testOnlyContext(),
                                          Zone.defaultZone(),
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationHandlerTest.java
index bfd6a35cc2e..2c84e2d8ad4 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ApplicationHandlerTest.java
@@ -222,13 +222,13 @@ public class ApplicationHandlerTest {
     }
 
     private void deleteAndAssertOKResponseMocked(ApplicationId applicationId, boolean fullAppIdInUrl) throws IOException {
-        long sessionId = tenantRepository.getTenant(applicationId.tenant()).getApplicationRepo().requireActiveSessionOf(applicationId);
+        long sessionId = tenantRepository.getTenant(applicationId.tenant()).getApplicationRepo().getSessionIdForApplication(applicationId);
         deleteAndAssertResponse(applicationId, Zone.defaultZone(), Response.Status.OK, null, fullAppIdInUrl);
         assertNull(tenantRepository.getTenant(applicationId.tenant()).getLocalSessionRepo().getSession(sessionId));
     }
 
     private void deleteAndAssertOKResponse(Tenant tenant, ApplicationId applicationId) throws IOException {
-        long sessionId = tenant.getApplicationRepo().requireActiveSessionOf(applicationId);
+        long sessionId = tenant.getApplicationRepo().getSessionIdForApplication(applicationId);
         deleteAndAssertResponse(applicationId, Zone.defaultZone(), Response.Status.OK, null, true);
         assertNull(tenant.getLocalSessionRepo().getSession(sessionId));
     }
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/HostHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/HostHandlerTest.java
index 1db70956407..2d3dcc592f7 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/HostHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/HostHandlerTest.java
@@ -46,8 +46,7 @@ public class HostHandlerTest {
     private HostHandler hostHandler;
 
     static void addMockApplication(Tenant tenant, ApplicationId applicationId, long sessionId) {
-        tenant.getApplicationRepo().createApplication(applicationId);
-        tenant.getApplicationRepo().createPutTransaction(applicationId, sessionId).commit();
+        tenant.getApplicationRepo().createPutApplicationTransaction(applicationId, sessionId).commit();
         ApplicationPackage app = FilesApplicationPackage.fromFile(testApp);
         tenant.getLocalSessionRepo().addSession(new SessionHandlerTest.MockSession(sessionId, app, applicationId));
         TestComponentRegistry componentRegistry = new TestComponentRegistry.Builder()
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandlerTest.java
index f97bc443a38..f57e7f09b39 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/ListApplicationsHandlerTest.java
@@ -51,17 +51,17 @@ public class ListApplicationsHandlerTest {
         final String url = "http://myhost:14000/application/v2/tenant/mytenant/application/";
         assertResponse(url, Response.Status.OK,
                 "[]");
-        ApplicationId id1 = ApplicationId.from("mytenant", "foo", "quux");
-        applicationRepo.createApplication(id1);
-        applicationRepo.createPutTransaction(id1, 1).commit();
+        applicationRepo.createPutApplicationTransaction(
+                new ApplicationId.Builder().tenant("tenant").applicationName("foo").instanceName("quux").build(),
+                1).commit();
         assertResponse(url, Response.Status.OK,
                 "[\"" + url + "foo/environment/dev/region/us-east/instance/quux\"]");
-        ApplicationId id2 = ApplicationId.from("mytenant", "bali", "quux");
-        applicationRepo.createApplication(id2);
-        applicationRepo.createPutTransaction(id2, 1).commit();
+        applicationRepo.createPutApplicationTransaction(
+                new ApplicationId.Builder().tenant("tenant").applicationName("bali").instanceName("quux").build(),
+                1).commit();
         assertResponse(url, Response.Status.OK,
-                "[\"" + url + "bali/environment/dev/region/us-east/instance/quux\"," +
-                        "\"" + url + "foo/environment/dev/region/us-east/instance/quux\"]"
+                "[\"" + url + "foo/environment/dev/region/us-east/instance/quux\"," +
+                        "\"" + url + "bali/environment/dev/region/us-east/instance/quux\"]"
         );
     }
 
@@ -82,12 +82,12 @@ public class ListApplicationsHandlerTest {
 
     @Test
     public void require_that_listing_works_with_multiple_tenants() throws Exception {
-        ApplicationId id1 = ApplicationId.from("mytenant", "foo", "quux");
-        applicationRepo.createApplication(id1);
-        applicationRepo.createPutTransaction(id1, 1).commit();
-        ApplicationId id2 = ApplicationId.from("foobar", "quux", "foo");
-        applicationRepo2.createApplication(id2);
-        applicationRepo2.createPutTransaction(id2, 1).commit();
+        applicationRepo.createPutApplicationTransaction(new ApplicationId.Builder()
+                .tenant("tenant")
+                .applicationName("foo").instanceName("quux").build(), 1).commit();
+        applicationRepo2.createPutApplicationTransaction(new ApplicationId.Builder()
+                .tenant("tenant")
+                .applicationName("quux").instanceName("foo").build(), 1).commit();
         String url = "http://myhost:14000/application/v2/tenant/mytenant/application/";
         assertResponse(url, Response.Status.OK,
                 "[\"" + url + "foo/environment/dev/region/us-east/instance/quux\"]");
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionActiveHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionActiveHandlerTest.java
index 858d1e0eaa7..380b76c30af 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionActiveHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionActiveHandlerTest.java
@@ -323,9 +323,6 @@ public class SessionActiveHandlerTest extends SessionHandlerTest {
                                             Optional.of(AllocatedHosts.withHosts(Collections.singleton(new HostSpec("bar", Collections.emptyList())))));
             session = createRemoteSession(sessionId, initialStatus, zkClient);
             addLocalSession(sessionId, deployData, zkClient);
-            tenantRepository.getTenant(tenantName).getApplicationRepo().createApplication(ApplicationId.from(tenantName.value(),
-                                                                                                             deployData.getApplicationName(),
-                                                                                                             InstanceName.defaultName().value()));
             metaData = localRepo.getSession(sessionId).getMetaData();
             actResponse = handler.handle(SessionHandlerTest.createTestRequest(pathPrefix, HttpRequest.Method.PUT, Cmd.ACTIVE, sessionId, subPath));
             return this;
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionCreateHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionCreateHandlerTest.java
index 7f7f71a1fe8..94d3b126bd7 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionCreateHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/v2/SessionCreateHandlerTest.java
@@ -203,8 +203,7 @@ public class SessionCreateHandlerTest extends SessionHandlerTest {
                               .applicationName("foo")
                               .instanceName("quux")
                               .build();
-        applicationRepo.createApplication(fooId);
-        applicationRepo.createPutTransaction(fooId, 2).commit();
+        applicationRepo.createPutApplicationTransaction(fooId, 2).commit();
         assertFromParameter("3", "http://myhost:40555/application/v2/tenant/" + tenant + "/application/foo/environment/test/region/baz/instance/quux");
         localSessionRepo.addSession(new SessionHandlerTest.MockSession(5l, FilesApplicationPackage.fromFile(testApp)));
         ApplicationId bioId = new ApplicationId.Builder()
@@ -212,8 +211,7 @@ public class SessionCreateHandlerTest extends SessionHandlerTest {
                               .applicationName("foobio")
                               .instanceName("quux")
                               .build();
-        applicationRepo.createApplication(bioId);
-        applicationRepo.createPutTransaction(bioId, 5).commit();
+        applicationRepo.createPutApplicationTransaction(bioId, 5).commit();
         assertFromParameter("6", "http://myhost:40555/application/v2/tenant/" + tenant + "/application/foobio/environment/staging/region/baz/instance/quux");
     }
 
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/session/LocalSessionTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/session/LocalSessionTest.java
index a4432dcbfcd..e7db4dcf58f 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/session/LocalSessionTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/session/LocalSessionTest.java
@@ -196,14 +196,12 @@ public class LocalSessionTest {
         zkClient.write(Collections.singletonMap(new Version(0, 0, 0), new MockFileRegistry()));
         File sessionDir = new File(tenantFileSystemDirs.sessionsPath(), String.valueOf(sessionId));
         sessionDir.createNewFile();
-        TenantApplications applications = TenantApplications.create(curator, new MockReloadHandler(), tenant);
-        applications.createApplication(zkc.readApplicationId());
         return new LocalSession(tenant, sessionId, preparer,
                 new SessionContext(
                         FilesApplicationPackage.fromFile(testApp),
                         zkc,
                         sessionDir,
-                        applications,
+                        TenantApplications.create(curator, new MockReloadHandler(), tenant),
                         new HostRegistry<>(),
                         superModelGenerationCounter,
                         flagSource));
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/session/RemoteSessionTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/session/RemoteSessionTest.java
index d5d0fe72dbe..a7b74e69a21 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/session/RemoteSessionTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/session/RemoteSessionTest.java
@@ -3,26 +3,23 @@ package com.yahoo.vespa.config.server.session;
 
 import com.google.common.io.Files;
 import com.yahoo.cloud.config.ConfigserverConfig;
-import com.yahoo.component.Version;
 import com.yahoo.config.application.api.ApplicationPackage;
 import com.yahoo.config.model.NullConfigModelRegistry;
-import com.yahoo.config.model.api.Model;
-import com.yahoo.config.model.api.ModelContext;
-import com.yahoo.config.model.api.ModelCreateResult;
-import com.yahoo.config.model.api.ModelFactory;
-import com.yahoo.config.model.api.ValidationParameters;
+import com.yahoo.config.model.api.*;
 import com.yahoo.config.model.deploy.DeployState;
-import com.yahoo.config.model.test.MockApplicationPackage;
 import com.yahoo.config.provision.ApplicationId;
 import com.yahoo.config.provision.TenantName;
-import com.yahoo.vespa.config.server.TestComponentRegistry;
+import com.yahoo.config.model.test.MockApplicationPackage;
+import com.yahoo.component.Version;
 import com.yahoo.vespa.config.server.application.ApplicationSet;
-import com.yahoo.vespa.config.server.application.PermanentApplicationPackage;
 import com.yahoo.vespa.config.server.modelfactory.ModelFactoryRegistry;
-import com.yahoo.vespa.curator.Curator;
+import com.yahoo.vespa.config.server.TestComponentRegistry;
+import com.yahoo.vespa.config.server.application.PermanentApplicationPackage;
 import com.yahoo.vespa.curator.mock.MockCurator;
+import com.yahoo.vespa.curator.Curator;
 import com.yahoo.vespa.model.VespaModel;
 import com.yahoo.vespa.model.VespaModelFactory;
+
 import org.junit.Before;
 import org.junit.Test;
 
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRepositoryTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRepositoryTest.java
index 9bd5c5f1614..4046384005d 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRepositoryTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRepositoryTest.java
@@ -81,8 +81,6 @@ public class TenantRepositoryTest {
 
     @Test
     public void testListenersAdded() throws IOException, SAXException {
-        tenantRepository.getTenant(tenant1).getApplicationRepo().createApplication(ApplicationId.defaultId());
-        tenantRepository.getTenant(tenant1).getApplicationRepo().createPutTransaction(ApplicationId.defaultId(), 4).commit();
         tenantRepository.getTenant(tenant1).getReloadHandler().reloadConfig(ApplicationSet.fromSingle(
                 new Application(new VespaModel(MockApplicationPackage.createEmpty()),
                                 new ServerCache(),
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandlerTest.java
index 26a6f5e0c5f..5f18046cb81 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/tenant/TenantRequestHandlerTest.java
@@ -1,7 +1,6 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.config.server.tenant;
 
-import com.yahoo.component.Version;
 import com.yahoo.config.ConfigInstance;
 import com.yahoo.config.SimpletypesConfig;
 import com.yahoo.config.application.api.ApplicationPackage;
@@ -10,10 +9,9 @@ import com.yahoo.config.model.application.provider.BaseDeployLogger;
 import com.yahoo.config.model.application.provider.DeployData;
 import com.yahoo.config.model.application.provider.FilesApplicationPackage;
 import com.yahoo.config.model.application.provider.MockFileRegistry;
-import com.yahoo.config.provision.AllocatedHosts;
-import com.yahoo.config.provision.ApplicationId;
 import com.yahoo.config.provision.ApplicationName;
-import com.yahoo.config.provision.TenantName;
+import com.yahoo.config.provision.AllocatedHosts;
+import com.yahoo.component.Version;
 import com.yahoo.io.IOUtils;
 import com.yahoo.vespa.config.ConfigKey;
 import com.yahoo.vespa.config.ConfigPayload;
@@ -21,24 +19,27 @@ import com.yahoo.vespa.config.GetConfigRequest;
 import com.yahoo.vespa.config.protocol.ConfigResponse;
 import com.yahoo.vespa.config.protocol.DefContent;
 import com.yahoo.vespa.config.protocol.VespaVersion;
+import com.yahoo.vespa.config.server.application.ApplicationSet;
+import com.yahoo.vespa.config.server.host.HostRegistries;
 import com.yahoo.vespa.config.server.ReloadListener;
 import com.yahoo.vespa.config.server.ServerCache;
 import com.yahoo.vespa.config.server.TestComponentRegistry;
+import com.yahoo.vespa.config.server.rpc.UncompressedConfigResponseFactory;
 import com.yahoo.vespa.config.server.application.Application;
-import com.yahoo.vespa.config.server.application.ApplicationSet;
+import com.yahoo.config.provision.ApplicationId;
+import com.yahoo.config.provision.TenantName;
 import com.yahoo.vespa.config.server.deploy.ZooKeeperDeployer;
-import com.yahoo.vespa.config.server.host.HostRegistries;
 import com.yahoo.vespa.config.server.model.TestModelFactory;
 import com.yahoo.vespa.config.server.modelfactory.ModelFactoryRegistry;
 import com.yahoo.vespa.config.server.monitoring.MetricUpdater;
 import com.yahoo.vespa.config.server.monitoring.Metrics;
-import com.yahoo.vespa.config.server.rpc.UncompressedConfigResponseFactory;
 import com.yahoo.vespa.config.server.session.RemoteSession;
 import com.yahoo.vespa.config.server.session.SessionZooKeeperClient;
 import com.yahoo.vespa.curator.Curator;
 import com.yahoo.vespa.curator.mock.MockCurator;
 import com.yahoo.vespa.model.VespaModel;
 import com.yahoo.vespa.model.VespaModelFactory;
+
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -47,22 +48,11 @@ import org.xml.sax.SAXException;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
-import java.util.Set;
+import java.util.*;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.hamcrest.core.Is.is;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertThat;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 /**
  * @author Ulf Lilleengen
@@ -93,7 +83,7 @@ public class TenantRequestHandlerTest {
         Metrics sh = Metrics.createTestMetrics();
         List<ReloadListener> listeners = new ArrayList<>();
         listeners.add(listener);
-        server = new TenantRequestHandler(sh, tenant, listeners, new UncompressedConfigResponseFactory(), new HostRegistries(), curator);
+        server = new TenantRequestHandler(sh, tenant, listeners, new UncompressedConfigResponseFactory(), new HostRegistries());
         componentRegistry = new TestComponentRegistry.Builder()
                 .curator(curator)
                 .modelFactoryRegistry(createRegistry())
@@ -176,8 +166,6 @@ public class TenantRequestHandlerTest {
     public void testReloadConfig() throws IOException {
         ApplicationId applicationId = new ApplicationId.Builder().applicationName(ApplicationName.defaultName()).tenant(tenant).build();
 
-        server.applications().createApplication(applicationId);
-        server.applications().createPutTransaction(applicationId, 1).commit();
         server.reloadConfig(reloadConfig(1));
         assertThat(listener.reloaded.get(), is(1));
         // Using only payload list for this simple test
@@ -197,7 +185,6 @@ public class TenantRequestHandlerTest {
 
         listener.reloaded.set(0);
         feedApp(app2, 2, defaultApp(), true);
-        server.applications().createPutTransaction(applicationId, 2).commit();
         server.reloadConfig(reloadConfig(2L));
         configResponse = getConfigResponse(SimpletypesConfig.class, server, defaultApp(), vespaVersion, "");
         assertTrue(configResponse.isInternalRedeploy());
@@ -209,34 +196,19 @@ public class TenantRequestHandlerTest {
 
     @Test
     public void testRemoveApplication() {
-        ApplicationId appId = ApplicationId.from(tenant.value(), "default", "default");
-        server.reloadConfig(reloadConfig(1));
-        assertThat(listener.reloaded.get(), is(0));
-
-        server.applications().createApplication(appId);
-        server.applications().createPutTransaction(appId, 1).commit();
         server.reloadConfig(reloadConfig(1));
-        assertThat(listener.reloaded.get(), is(1));
-
         assertThat(listener.removed.get(), is(0));
-
-        server.removeApplication(appId);
-        assertThat(listener.removed.get(), is(0));
-
-        server.applications().createDeleteTransaction(appId).commit();
-        server.removeApplication(appId);
+        server.removeApplication(new ApplicationId.Builder().applicationName(ApplicationName.defaultName()).tenant(tenant).build());
         assertThat(listener.removed.get(), is(1));
     }
 
     @Test
     public void testResolveForAppId() {
         long id = 1L;
+        SessionZooKeeperClient zkc = new SessionZooKeeperClient(curator, TenantRepository.getSessionsPath(tenant).append(String.valueOf(id)));
         ApplicationId appId = new ApplicationId.Builder()
                               .tenant(tenant)
                               .applicationName("myapp").instanceName("myinst").build();
-        server.applications().createApplication(appId);
-        server.applications().createPutTransaction(appId, 1).commit();
-        SessionZooKeeperClient zkc = new SessionZooKeeperClient(curator, TenantRepository.getSessionsPath(tenant).append(String.valueOf(id)));
         zkc.writeApplicationId(appId);
         RemoteSession session = new RemoteSession(appId.tenant(), id, componentRegistry, zkc);
         server.reloadConfig(session.ensureApplicationLoaded());
@@ -274,8 +246,6 @@ public class TenantRequestHandlerTest {
     }
 
     private void feedAndReloadApp(File appDir, long sessionId, ApplicationId appId) throws IOException {
-        server.applications().createApplication(appId);
-        server.applications().createPutTransaction(appId, sessionId).commit();
         feedApp(appDir, sessionId, appId, false);
         SessionZooKeeperClient zkc = new SessionZooKeeperClient(curator, TenantRepository.getSessionsPath(tenant).append(String.valueOf(sessionId)));
         zkc.writeApplicationId(appId);
@@ -311,11 +281,9 @@ public class TenantRequestHandlerTest {
     @Test
     public void testHasApplication() {
         assertdefaultAppNotFound();
-        ApplicationId appId = ApplicationId.from(tenant.value(), "default", "default");
-        server.applications().createApplication(appId);
-        server.applications().createPutTransaction(appId, 1).commit();
         server.reloadConfig(reloadConfig(1));
-        assertTrue(server.hasApplication(appId, Optional.of(vespaVersion)));
+        assertTrue(server.hasApplication(new ApplicationId.Builder().applicationName(ApplicationName.defaultName()).tenant(tenant).build(),
+                                         Optional.of(vespaVersion)));
     }
 
     private void assertdefaultAppNotFound() {
@@ -324,13 +292,10 @@ public class TenantRequestHandlerTest {
 
     @Test
     public void testMultipleApplicationsReload() {
-        ApplicationId appId = ApplicationId.from(tenant.value(), "foo", "default");
         assertdefaultAppNotFound();
-        server.applications().createApplication(appId);
-        server.applications().createPutTransaction(appId, 1).commit();
         server.reloadConfig(reloadConfig(1, "foo"));
         assertdefaultAppNotFound();
-        assertTrue(server.hasApplication(appId,
+        assertTrue(server.hasApplication(new ApplicationId.Builder().tenant(tenant).applicationName("foo").build(),
                                          Optional.of(vespaVersion)));
         assertThat(server.resolveApplicationId("doesnotexist"), is(ApplicationId.defaultId()));
         assertThat(server.resolveApplicationId("mytesthost"), is(new ApplicationId.Builder()
@@ -343,8 +308,6 @@ public class TenantRequestHandlerTest {
         assertdefaultAppNotFound();
 
         VespaModel model = new VespaModel(FilesApplicationPackage.fromFile(new File("src/test/apps/app")));
-        server.applications().createApplication(ApplicationId.defaultId());
-        server.applications().createPutTransaction(ApplicationId.defaultId(), 1).commit();
         server.reloadConfig(ApplicationSet.fromSingle(new Application(model,
                                                                       new ServerCache(),
                                                                       1,
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/ApplicationMaintainer.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/ApplicationMaintainer.java
index 6ac2466ee7b..5e5b3546ced 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/ApplicationMaintainer.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/ApplicationMaintainer.java
@@ -51,6 +51,11 @@ public abstract class ApplicationMaintainer extends Maintainer {
         return pendingDeployments.size();
     }
 
+    /** Returns whether given application should be deployed at this moment in time */
+    protected boolean canDeployNow(ApplicationId application) {
+        return true;
+    }
+
     /**
      * Redeploy this application.
      *
@@ -70,18 +75,19 @@ public abstract class ApplicationMaintainer extends Maintainer {
     /** Returns the applications that should be maintained by this now. */
     protected abstract Set<ApplicationId> applicationsNeedingMaintenance();
 
-    /** Redeploy this application. */
+    /** Redeploy this application. A lock will be taken for the duration of the deployment activation */
     protected final void deployWithLock(ApplicationId application) {
         // An application might change its state between the time the set of applications is retrieved and the
         // time deployment happens. Lock the application and check if it's still active.
-        try {
-            try (Mutex lock = nodeRepository().lock(application, Duration.ofSeconds(10))) {
-                if ( ! isActive(application)) return; // became inactive since deployment was requested
-            }
-            deployer.deployFromLocalActive(application).ifPresent(deployment -> { // if deployed on this config server
-                log.log(LogLevel.DEBUG, this.getClass().getSimpleName() + " deploying " + application);
-                deployment.activate();
-            });
+        //
+        // Lock is acquired with a low timeout to reduce the chance of colliding with an external deployment.
+        try (Mutex lock = nodeRepository().lock(application, Duration.ofSeconds(1))) {
+            if ( ! isActive(application)) return; // became inactive since deployment was requested
+            if ( ! canDeployNow(application)) return; // redeployment is no longer needed
+            Optional<Deployment> deployment = deployer.deployFromLocalActive(application);
+            if ( ! deployment.isPresent()) return; // this will be done at another config server
+            log.log(LogLevel.DEBUG, this.getClass().getSimpleName() + " deploying " + application);
+            deployment.get().activate();
         } catch (RuntimeException e) {
             log.log(LogLevel.WARNING, "Exception on maintenance redeploy", e);
         } finally {
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/PeriodicApplicationMaintainer.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/PeriodicApplicationMaintainer.java
index 268362052f5..2525dbecca2 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/PeriodicApplicationMaintainer.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/PeriodicApplicationMaintainer.java
@@ -38,7 +38,8 @@ public class PeriodicApplicationMaintainer extends ApplicationMaintainer {
         this.start = clock.instant();
     }
 
-    private boolean canDeployNow(ApplicationId application) {
+    @Override
+    protected boolean canDeployNow(ApplicationId application) {
         // Don't deploy if a regular deploy just happened
         return getLastDeployTime(application).isBefore(nodeRepository().clock().instant().minus(minTimeBetweenRedeployments));
     }
diff --git a/zkfacade/src/test/java/com/yahoo/vespa/curator/CuratorCompletionWaiterTest.java b/zkfacade/src/test/java/com/yahoo/vespa/curator/CuratorCompletionWaiterTest.java
index d1ce744de7f..899737ec7fb 100644
--- a/zkfacade/src/test/java/com/yahoo/vespa/curator/CuratorCompletionWaiterTest.java
+++ b/zkfacade/src/test/java/com/yahoo/vespa/curator/CuratorCompletionWaiterTest.java
@@ -26,7 +26,6 @@ public class CuratorCompletionWaiterTest {
                 fail("Waiting failed due to timeout");
             }
         });
-        t1.start();
         notifier.notifyCompletion();
         t1.join();
     }