Introduce node IP address pool

A host that is supposed to run containers has a non-empty IP pool: A set of
IPv4 and/or IPv6 addresses that can be assigned to containers.

This PR adds a list of hostnames to this pool.  The intent is that the
hostnames and IPs match through resolving, but resolution may not yet be
available (until DNS changes propagate).

For now, only a list of hostnames are specified.  We may want to specify
(hostname, IP address) pairs or (hostname, IPv4, IPv6) triplets later, and the
serialization format allows for that by storing the hsotnames in an array of
objects, the object having a "hostname" field.

However the REST API is kept simpler for now: it exposes and allows patching of
an array of strings of a "additionalHostnames" field.

20 files changed, 306 insertions, 99 deletions

diff --git a/athenz-identity-provider-service/src/test/java/com/yahoo/vespa/hosted/athenz/instanceproviderservice/identitydocument/IdentityDocumentGeneratorTest.java b/athenz-identity-provider-service/src/test/java/com/yahoo/vespa/hosted/athenz/instanceproviderservice/identitydocument/IdentityDocumentGeneratorTest.java
index edda5593e79..0a757b5b17b 100644
--- a/athenz-identity-provider-service/src/test/java/com/yahoo/vespa/hosted/athenz/instanceproviderservice/identitydocument/IdentityDocumentGeneratorTest.java
+++ b/athenz-identity-provider-service/src/test/java/com/yahoo/vespa/hosted/athenz/instanceproviderservice/identitydocument/IdentityDocumentGeneratorTest.java
@@ -57,7 +57,7 @@ public class IdentityDocumentGeneratorTest {
                                                Generation.initial(),
                                                false);
         Node parentNode = Node.create("ostkid",
-                                      new IP.Config(Set.of("127.0.0.1"), Set.of()),
+                                      IP.Config.ofEmptyPool(Set.of("127.0.0.1")),
                                       parentHostname,
                                       new MockNodeFlavors().getFlavorOrThrow("default"),
                                       NodeType.host).build();
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/Node.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/Node.java
index 298404256b9..d0ee6229428 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/Node.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/Node.java
@@ -55,7 +55,7 @@ public final class Node implements Nodelike {
     /** Creates a node builder in the initial state (reserved) */
     public static Node.Builder createDockerNode(Set<String> ipAddresses, String hostname, String parentHostname, NodeResources resources, NodeType type) {
         return new Node.Builder("fake-" + hostname, hostname, new Flavor(resources), State.reserved, type)
-                .ipConfig(ipAddresses, Set.of())
+                .ipConfig(IP.Config.ofEmptyPool(ipAddresses))
                 .parentHostname(parentHostname);
     }
 
@@ -573,8 +573,8 @@ public final class Node implements Nodelike {
             return this;
         }
 
-        public Builder ipConfig(Set<String> primary, Set<String> pool) {
-            this.ipConfig = new IP.Config(primary, pool);
+        public Builder ipConfigWithEmptyPool(Set<String> primary) {
+            this.ipConfig = IP.Config.ofEmptyPool(primary);
             return this;
         }
 
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java
index e5202dfd3c0..6094b497fff 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/CapacityChecker.java
@@ -135,12 +135,12 @@ public class CapacityChecker {
         for (var host : hosts) {
             NodeResources hostResources = host.flavor().resources();
             int occupiedIps = 0;
-            Set<String> ipPool = host.ipConfig().pool().asSet();
+            Set<String> ipPool = host.ipConfig().pool().getIpSet();
             for (var child : nodeChildren.get(host)) {
                 hostResources = hostResources.subtract(child.resources().justNumbers());
                 occupiedIps += child.ipConfig().primary().stream().filter(ipPool::contains).count();
             }
-            availableResources.put(host, new AllocationResources(hostResources, host.ipConfig().pool().asSet().size() - occupiedIps));
+            availableResources.put(host, new AllocationResources(hostResources, host.ipConfig().pool().getIpSet().size() - occupiedIps));
         }
 
         return availableResources;
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/Address.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/Address.java
new file mode 100644
index 00000000000..bdef06f1070
--- /dev/null
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/Address.java
@@ -0,0 +1,49 @@
+// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.hosted.provision.node;
+
+import java.util.Objects;
+
+/**
+ * Address info about a container that might run on a host.
+ *
+ * @author hakon
+ */
+public class Address {
+    private final String hostname;
+
+    public Address(String hostname) {
+        this.hostname = validateHostname(hostname, "hostname");
+    }
+
+    public String hostname() {
+        return hostname;
+    }
+
+    @Override
+    public String toString() {
+        return "Address{" +
+                "hostname='" + hostname + '\'' +
+                '}';
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Address address = (Address) o;
+        return hostname.equals(address.hostname);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(hostname);
+    }
+
+    private String validateHostname(String value, String name) {
+        Objects.requireNonNull(value, name + " cannot be null");
+        if (value.isEmpty()) {
+            throw new IllegalArgumentException(name + " cannot be empty");
+        }
+        return value;
+    }
+}
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java
index 955936931be..41d6c1e5425 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java
@@ -60,15 +60,29 @@ public class IP {
     /** IP configuration of a node */
     public static class Config {
 
-        public static final Config EMPTY = new Config(Set.of(), Set.of());
+        public static final Config EMPTY = Config.ofEmptyPool(Set.of());
 
         private final Set<String> primary;
         private final Pool pool;
 
-        /** DO NOT USE in non-test code. Public for serialization purposes. */
+        public static Config ofEmptyPool(Set<String> primary) {
+            return new Config(primary, Set.of(), List.of());
+        }
+
+        public static Config of(Set<String> primary, Set<String> ipPool, List<Address> addressPool) {
+            return new Config(primary, ipPool, addressPool);
+        }
+
+        /** LEGACY TEST CONSTRUCTOR - use of() variants and/or the with- methods. */
         public Config(Set<String> primary, Set<String> pool) {
+            this(primary, pool, List.of());
+        }
+
+        /** DO NOT USE: Public for NodeSerializer. */
+        public Config(Set<String> primary, Set<String> pool, List<Address> addresses) {
             this.primary = ImmutableSet.copyOf(Objects.requireNonNull(primary, "primary must be non-null"));
-            this.pool = Pool.of(Objects.requireNonNull(pool, "pool must be non-null"));
+            this.pool = Pool.of(Objects.requireNonNull(pool, "pool must be non-null"),
+                                Objects.requireNonNull(addresses, "addresses must be non-null"));
         }
 
         /** The primary addresses of this. These addresses are used when communicating with the node itself */
@@ -82,13 +96,13 @@ public class IP {
         }
 
         /** Returns a copy of this with pool set to given value */
-        public Config with(Pool pool) {
-            return new Config(primary, pool.asSet());
+        public Config withPool(Pool pool) {
+            return new Config(primary, pool.getIpSet(), pool.getAddressList());
         }
 
         /** Returns a copy of this with pool set to given value */
-        public Config with(Set<String> primary) {
-            return new Config(primary, pool.asSet());
+        public Config withPrimary(Set<String> primary) {
+            return new Config(primary, pool.getIpSet(), pool.getAddressList());
         }
 
         @Override
@@ -107,7 +121,7 @@ public class IP {
 
         @Override
         public String toString() {
-            return String.format("ip config primary=%s pool=%s", primary, pool.asSet());
+            return String.format("ip config primary=%s pool=%s", primary, pool.getIpSet());
         }
 
         /**
@@ -124,8 +138,8 @@ public class IP {
                     var addresses = new HashSet<>(node.ipConfig().primary());
                     var otherAddresses = new HashSet<>(other.ipConfig().primary());
                     if (node.type().isHost()) { // Addresses of a host can never overlap with any other nodes
-                        addresses.addAll(node.ipConfig().pool().asSet());
-                        otherAddresses.addAll(other.ipConfig().pool().asSet());
+                        addresses.addAll(node.ipConfig().pool().getIpSet());
+                        otherAddresses.addAll(other.ipConfig().pool().getIpSet());
                     }
                     otherAddresses.retainAll(addresses);
                     if (!otherAddresses.isEmpty())
@@ -157,18 +171,18 @@ public class IP {
     }
 
     /** A list of IP addresses and their protocol */
-    public static class Addresses {
+    public static class IpAddresses {
 
-        private final Set<String> addresses;
+        private final Set<String> ipAddresses;
         private final Protocol protocol;
 
-        private Addresses(Set<String> addresses, Protocol protocol) {
-            this.addresses = ImmutableSet.copyOf(Objects.requireNonNull(addresses, "addresses must be non-null"));
+        private IpAddresses(Set<String> ipAddresses, Protocol protocol) {
+            this.ipAddresses = ImmutableSet.copyOf(Objects.requireNonNull(ipAddresses, "addresses must be non-null"));
             this.protocol = Objects.requireNonNull(protocol, "type must be non-null");
         }
 
         public Set<String> asSet() {
-            return addresses;
+            return ipAddresses;
         }
 
         /** The protocol of addresses in this */
@@ -177,20 +191,20 @@ public class IP {
         }
 
         /** Create addresses of the given set */
-        private static Addresses of(Set<String> addresses) {
+        private static IpAddresses of(Set<String> addresses) {
             long ipv6AddrCount = addresses.stream().filter(IP::isV6).count();
             if (ipv6AddrCount == addresses.size()) { // IPv6-only
-                return new Addresses(addresses, Protocol.ipv6);
+                return new IpAddresses(addresses, Protocol.ipv6);
             }
 
             long ipv4AddrCount = addresses.stream().filter(IP::isV4).count();
             if (ipv4AddrCount == addresses.size()) { // IPv4-only
-                return new Addresses(addresses, Protocol.ipv4);
+                return new IpAddresses(addresses, Protocol.ipv4);
             }
 
             // If we're dual-stacked, we must must have an equal number of addresses of each protocol.
             if (ipv4AddrCount == ipv6AddrCount) {
-                return new Addresses(addresses, Protocol.dualStack);
+                return new IpAddresses(addresses, Protocol.dualStack);
             }
 
             throw new IllegalArgumentException(String.format("Dual-stacked IP address list must have an " +
@@ -208,15 +222,28 @@ public class IP {
     }
 
     /**
-     * A pool of IP addresses from which an allocation can be made.
+     * A pool of addresses from which an allocation can be made.
      *
      * Addresses in this are available for use by Docker containers
      */
     public static class Pool {
 
-        private final Addresses addresses;
+        private final IpAddresses ipAddresses;
+        private final List<Address> addresses;
 
-        private Pool(Addresses addresses) {
+        /** Creates an empty pool. */
+        public static Pool of() {
+            return of(Set.of(), List.of());
+        }
+
+        /** Create a new pool containing given ipAddresses */
+        public static Pool of(Set<String> ipAddresses, List<Address> addresses) {
+            IpAddresses ips = IpAddresses.of(ipAddresses);
+            return new Pool(ips, addresses);
+        }
+
+        private Pool(IpAddresses ipAddresses, List<Address> addresses) {
+            this.ipAddresses = Objects.requireNonNull(ipAddresses, "ipAddresses must be non-null");
             this.addresses = Objects.requireNonNull(addresses, "addresses must be non-null");
         }
 
@@ -227,6 +254,12 @@ public class IP {
          * @return an allocation from the pool, if any can be made
          */
         public Optional<Allocation> findAllocation(LockedNodeList nodes, NameResolver resolver) {
+            if (ipAddresses.protocol == IpAddresses.Protocol.ipv4) {
+                return findUnused(nodes).stream()
+                        .findFirst()
+                        .map(addr -> Allocation.ofIpv4(addr, resolver));
+            }
+
             var unusedAddresses = findUnused(nodes);
             var allocation = unusedAddresses.stream()
                                             .filter(IP::isV6)
@@ -248,64 +281,47 @@ public class IP {
          * @param nodes a list of all nodes in the repository
          */
         public Set<String> findUnused(NodeList nodes) {
-            var unusedAddresses = new LinkedHashSet<>(asSet());
-            nodes.matching(node -> node.ipConfig().primary().stream().anyMatch(ip -> asSet().contains(ip)))
+            var unusedAddresses = new LinkedHashSet<>(getIpSet());
+            nodes.matching(node -> node.ipConfig().primary().stream().anyMatch(ip -> getIpSet().contains(ip)))
                  .forEach(node -> unusedAddresses.removeAll(node.ipConfig().primary()));
             return Collections.unmodifiableSet(unusedAddresses);
         }
 
-        public Set<String> asSet() {
-            return addresses.asSet();
+        public IpAddresses.Protocol getProtocol() {
+            return ipAddresses.protocol;
         }
 
-        public boolean isEmpty() {
-            return asSet().isEmpty();
+        public Set<String> getIpSet() {
+            return ipAddresses.asSet();
         }
 
-        @Override
-        public boolean equals(Object o) {
-            if (this == o) return true;
-            if (o == null || getClass() != o.getClass()) return false;
-            Pool that = (Pool) o;
-            return Objects.equals(addresses, that.addresses);
+        public List<Address> getAddressList() {
+            return addresses;
         }
 
-        @Override
-        public int hashCode() {
-            return Objects.hash(addresses);
+        public boolean isEmpty() {
+            return getIpSet().isEmpty();
         }
 
-        /** Create a new pool containing given ipAddresses */
-        public static Pool of(Set<String> ipAddresses) {
-            var addresses = Addresses.of(ipAddresses);
-            if (addresses.protocol() == Addresses.Protocol.ipv4) {
-                return new Ipv4Pool(addresses);
-            }
-            return new Pool(addresses);
+        public Pool withIpAddresses(Set<String> ipAddresses) {
+            return Pool.of(ipAddresses, addresses);
         }
 
-        /** Validates and returns the given IP address pool */
-        public static Set<String> require(Set<String> pool) {
-            return of(pool).asSet();
+        public Pool withAddresses(List<Address> addresses) {
+            return Pool.of(ipAddresses.ipAddresses, addresses);
         }
 
-    }
-
-    /** A pool of IPv4-only addresses from which an allocation can be made. */
-    public static class Ipv4Pool extends Pool {
-
-        private Ipv4Pool(Addresses addresses) {
-            super(addresses);
-            if (addresses.protocol() != Addresses.Protocol.ipv4) {
-                throw new IllegalArgumentException("Protocol of addresses must be " + Addresses.Protocol.ipv4);
-            }
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            Pool that = (Pool) o;
+            return Objects.equals(ipAddresses, that.ipAddresses);
         }
 
         @Override
-        public Optional<Allocation> findAllocation(LockedNodeList nodes, NameResolver resolver) {
-            return findUnused(nodes).stream()
-                                    .findFirst()
-                                    .map(addr -> Allocation.ofIpv4(addr, resolver));
+        public int hashCode() {
+            return Objects.hash(ipAddresses);
         }
 
     }
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializer.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializer.java
index 0f171351fba..cd794531473 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializer.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializer.java
@@ -26,6 +26,7 @@ import com.yahoo.slime.Slime;
 import com.yahoo.slime.SlimeUtils;
 import com.yahoo.slime.Type;
 import com.yahoo.vespa.hosted.provision.Node;
+import com.yahoo.vespa.hosted.provision.node.Address;
 import com.yahoo.vespa.hosted.provision.node.Agent;
 import com.yahoo.vespa.hosted.provision.node.Allocation;
 import com.yahoo.vespa.hosted.provision.node.Generation;
@@ -66,6 +67,8 @@ public class NodeSerializer {
     private static final String hostnameKey = "hostname";
     private static final String ipAddressesKey = "ipAddresses";
     private static final String ipAddressPoolKey = "additionalIpAddresses";
+    private static final String containersKey = "containers";
+    private static final String containerHostnameKey = "hostname";
     private static final String idKey = "openStackId";
     private static final String parentHostnameKey = "parentHostname";
     private static final String historyKey = "history";
@@ -146,7 +149,8 @@ public class NodeSerializer {
     private void toSlime(Node node, Cursor object) {
         object.setString(hostnameKey, node.hostname());
         toSlime(node.ipConfig().primary(), object.setArray(ipAddressesKey));
-        toSlime(node.ipConfig().pool().asSet(), object.setArray(ipAddressPoolKey));
+        toSlime(node.ipConfig().pool().getIpSet(), object.setArray(ipAddressPoolKey));
+        toSlime(node.ipConfig().pool().getAddressList(), object);
         object.setString(idKey, node.id());
         node.parentHostname().ifPresent(hostname -> object.setString(parentHostnameKey, hostname));
         toSlime(node.flavor(), object);
@@ -214,6 +218,14 @@ public class NodeSerializer {
         ipAddresses.stream().map(IP::parse).sorted(IP.NATURAL_ORDER).map(IP::asString).forEach(array::addString);
     }
 
+    private void toSlime(List<Address> addresses, Cursor object) {
+        if (addresses.isEmpty()) return;
+        Cursor addressCursor = object.setArray(containersKey);
+        addresses.forEach(address -> {
+            addressCursor.addObject().setString(containerHostnameKey, address.hostname());
+        });
+    }
+
     // ---------------- Deserialization --------------------------------------------------
 
     public Node fromJson(Node.State state, byte[] data) {
@@ -232,7 +244,8 @@ public class NodeSerializer {
         Flavor flavor = flavorFromSlime(object);
         return new Node(object.field(idKey).asString(),
                         new IP.Config(ipAddressesFromSlime(object, ipAddressesKey),
-                                      ipAddressesFromSlime(object, ipAddressPoolKey)),
+                                      ipAddressesFromSlime(object, ipAddressPoolKey),
+                                      addressesFromSlime(object)),
                         object.field(hostnameKey).asString(),
                         parentHostnameFromSlime(object),
                         flavor,
@@ -358,6 +371,16 @@ public class NodeSerializer {
         return ipAddresses.build();
     }
 
+    private List<Address> addressesFromSlime(Inspector object) {
+        Inspector addressesField = object.field(containersKey);
+        if (addressesField.children() == 0)
+            return List.of();
+        List<Address> addresses = new ArrayList<>(addressesField.children());
+        addressesField.traverse((ArrayTraverser) (i, elem) ->
+                addresses.add(new Address(elem.field(containerHostnameKey).asString())));
+        return addresses;
+    }
+
     private Optional<String> modelNameFromSlime(Inspector object) {
         if (object.field(modelNameKey).valid()) {
             return Optional.of(object.field(modelNameKey).asString());
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodePatcher.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodePatcher.java
index f2755176124..832310cf2c9 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodePatcher.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodePatcher.java
@@ -15,6 +15,7 @@ import com.yahoo.slime.SlimeUtils;
 import com.yahoo.slime.Type;
 import com.yahoo.vespa.hosted.provision.LockedNodeList;
 import com.yahoo.vespa.hosted.provision.Node;
+import com.yahoo.vespa.hosted.provision.node.Address;
 import com.yahoo.vespa.hosted.provision.node.Agent;
 import com.yahoo.vespa.hosted.provision.node.Allocation;
 import com.yahoo.vespa.hosted.provision.node.IP;
@@ -26,6 +27,7 @@ import java.io.InputStream;
 import java.io.UncheckedIOException;
 import java.time.Clock;
 import java.time.Instant;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -116,9 +118,11 @@ public class NodePatcher {
             case "parentHostname" :
                 return node.withParentHostname(asString(value));
             case "ipAddresses" :
-                return IP.Config.verify(node.with(node.ipConfig().with(asStringSet(value))), memoizedNodes.get());
+                return IP.Config.verify(node.with(node.ipConfig().withPrimary(asStringSet(value))), memoizedNodes.get());
             case "additionalIpAddresses" :
-                return IP.Config.verify(node.with(node.ipConfig().with(IP.Pool.of(asStringSet(value)))), memoizedNodes.get());
+                return IP.Config.verify(node.with(node.ipConfig().withPool(node.ipConfig().pool().withIpAddresses(asStringSet(value)))), memoizedNodes.get());
+            case "additionalHostnames" :
+                return IP.Config.verify(node.with(node.ipConfig().withPool(node.ipConfig().pool().withAddresses(asAddressList(value)))), memoizedNodes.get());
             case WANT_TO_RETIRE :
             case WANT_TO_DEPROVISION :
                 boolean wantToRetire = asOptionalBoolean(root.field(WANT_TO_RETIRE)).orElse(node.status().wantToRetire());
@@ -212,6 +216,22 @@ public class NodePatcher {
         return strings;
     }
 
+    private List<Address> asAddressList(Inspector field) {
+        if ( ! field.type().equals(Type.ARRAY))
+            throw new IllegalArgumentException("Expected an ARRAY value, got a " + field.type());
+
+        List<Address> addresses = new ArrayList<>(field.entries());
+        for (int i = 0; i < field.entries(); i++) {
+            Inspector entry = field.entry(i);
+            if ( ! entry.type().equals(Type.STRING))
+                throw new IllegalArgumentException("Expected a STRING value, got a " + entry.type());
+            Address address = new Address(entry.asString());
+            addresses.add(address);
+        }
+
+        return addresses;
+    }
+
     private Node patchRequiredDiskSpeed(Node node, String value) {
         Optional<Allocation> allocation = node.allocation();
         if (allocation.isPresent())
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesResponse.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesResponse.java
index 39375494d01..3a9246379cf 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesResponse.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesResponse.java
@@ -15,6 +15,7 @@ import com.yahoo.slime.Slime;
 import com.yahoo.vespa.applicationmodel.HostName;
 import com.yahoo.vespa.hosted.provision.Node;
 import com.yahoo.vespa.hosted.provision.NodeRepository;
+import com.yahoo.vespa.hosted.provision.node.Address;
 import com.yahoo.vespa.hosted.provision.node.History;
 import com.yahoo.vespa.hosted.provision.node.filter.NodeFilter;
 import com.yahoo.vespa.orchestrator.Orchestrator;
@@ -186,7 +187,8 @@ class NodesResponse extends HttpResponse {
         object.setBool("wantToDeprovision", node.status().wantToDeprovision());
         toSlime(node.history(), object.setArray("history"));
         ipAddressesToSlime(node.ipConfig().primary(), object.setArray("ipAddresses"));
-        ipAddressesToSlime(node.ipConfig().pool().asSet(), object.setArray("additionalIpAddresses"));
+        ipAddressesToSlime(node.ipConfig().pool().getIpSet(), object.setArray("additionalIpAddresses"));
+        addressesToSlime(node.ipConfig().pool().getAddressList(), object);
         node.reports().toSlime(object, "reports");
         node.modelName().ifPresent(modelName -> object.setString("modelName", modelName));
         node.switchHostname().ifPresent(switchHostname -> object.setString("switchHostname", switchHostname));
@@ -229,6 +231,13 @@ class NodesResponse extends HttpResponse {
         ipAddresses.forEach(array::addString);
     }
 
+    private void addressesToSlime(List<Address> addresses, Cursor object) {
+        if (addresses.isEmpty()) return;
+        // When/if Address becomes richer: add another field (e.g. "addresses") and expand to array of objects
+        Cursor addressesArray = object.setArray("additionalHostnames");
+        addresses.forEach(address -> addressesArray.addString(address.hostname()));
+    }
+
     private String lastElement(String path) {
         if (path.endsWith("/"))
             path = path.substring(0, path.length()-1);
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiHandler.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiHandler.java
index 59604d094fa..304cebb3c01 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiHandler.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiHandler.java
@@ -257,7 +257,7 @@ public class NodesV2ApiHandler extends LoggingRequestHandler {
         inspector.field("additionalIpAddresses").traverse((ArrayTraverser) (i, item) -> ipAddressPool.add(item.asString()));
 
         Node.Builder builder = Node.create(inspector.field("openStackId").asString(),
-                                           new IP.Config(ipAddresses, ipAddressPool),
+                                           IP.Config.of(ipAddresses, ipAddressPool, List.of()),
                                            inspector.field("hostname").asString(),
                                            flavorFromSlime(inspector),
                                            nodeTypeFromSlime(inspector.field("type")));
diff --git a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/testutils/MockNodeRepository.java b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/testutils/MockNodeRepository.java
index fb78e76f0c7..b24d2417db5 100644
--- a/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/testutils/MockNodeRepository.java
+++ b/node-repository/src/main/java/com/yahoo/vespa/hosted/provision/testutils/MockNodeRepository.java
@@ -206,11 +206,11 @@ public class MockNodeRepository extends NodeRepository {
 
     private IP.Config ipConfig(int nodeIndex, int primarySize, int poolSize) {
         var primary = new LinkedHashSet<String>();
-        var pool = new LinkedHashSet<String>();
+        var ipPool = new LinkedHashSet<String>();
         for (int i = 1; i <= primarySize + poolSize; i++) {
             var set = primary;
             if (i > primarySize) {
-                set = pool;
+                set = ipPool;
             }
             var rootName = "test-node-primary";
             if (i > primarySize) {
@@ -226,7 +226,7 @@ public class MockNodeRepository extends NodeRepository {
                 set.add(ipv4Address);
             }
         }
-        return new IP.Config(primary, pool);
+        return IP.Config.of(primary, ipPool, List.of());
     }
 
     private IP.Config ipConfig(int nodeIndex) {
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/maintenance/DynamicProvisioningMaintainerTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/maintenance/DynamicProvisioningMaintainerTest.java
index c08e51bf0cc..478376bc0cd 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/maintenance/DynamicProvisioningMaintainerTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/maintenance/DynamicProvisioningMaintainerTest.java
@@ -66,9 +66,9 @@ public class DynamicProvisioningMaintainerTest {
         assertTrue("No IP addresses assigned",
                    Stream.of(host3, host4, host41).map(node -> node.ipConfig().primary()).allMatch(Set::isEmpty));
 
-        Node host3new = host3.with(host3.ipConfig().with(Set.of("::3:0")));
-        Node host4new = host4.with(host4.ipConfig().with(Set.of("::4:0")));
-        Node host41new = host41.with(host41.ipConfig().with(Set.of("::4:1", "::4:2")));
+        Node host3new = host3.with(host3.ipConfig().withPrimary(Set.of("::3:0")));
+        Node host4new = host4.with(host4.ipConfig().withPrimary(Set.of("::4:0")));
+        Node host41new = host41.with(host41.ipConfig().withPrimary(Set.of("::4:1", "::4:2")));
 
         tester.maintainer.maintain();
         assertEquals(host3new, tester.nodeRepository.getNode("host3").get());
@@ -290,7 +290,7 @@ public class DynamicProvisioningMaintainerTest {
                             Generation.initial(),
                             false));
             Node.Builder builder = Node.create("fake-id-" + hostname, hostname, flavor, state, nodeType)
-                    .ipConfig(state == Node.State.active ? Set.of("::1") : Set.of(), Set.of());
+                    .ipConfigWithEmptyPool(state == Node.State.active ? Set.of("::1") : Set.of());
             parentHostname.ifPresent(builder::parentHostname);
             allocation.ifPresent(builder::allocation);
             return builder.build();
@@ -382,16 +382,18 @@ public class DynamicProvisioningMaintainerTest {
             if (node.parentHostname().isPresent()) return node;
             int hostIndex = Integer.parseInt(node.hostname().replaceAll("^[a-z]+|-\\d+$", ""));
             Set<String> addresses = Set.of("::" + hostIndex + ":0");
-            Set<String> pool = new HashSet<>();
+            Set<String> ipAddressPool = new HashSet<>();
             if (!behaviours.contains(Behaviour.failDnsUpdate)) {
                 nameResolver.addRecord(node.hostname(), addresses.iterator().next());
                 for (int i = 1; i <= 2; i++) {
                     String ip = "::" + hostIndex + ":" + i;
-                    pool.add(ip);
+                    ipAddressPool.add(ip);
                     nameResolver.addRecord(node.hostname() + "-" + i, ip);
                 }
             }
-            return node.with(node.ipConfig().with(addresses).with(IP.Pool.of(pool)));
+
+            IP.Pool pool = node.ipConfig().pool().withIpAddresses(ipAddressPool);
+            return node.with(node.ipConfig().withPrimary(addresses).withPool(pool));
         }
 
         enum Behaviour {
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/node/IPTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/node/IPTest.java
index a209ea206d3..fb9c1ad0e5a 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/node/IPTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/node/IPTest.java
@@ -177,7 +177,7 @@ public class IPTest {
         }
 
         IP.Pool pool = node.ipConfig().pool();
-        assertNotEquals(dualStack, pool instanceof IP.Ipv4Pool);
+        assertNotEquals(dualStack, pool.getProtocol() == IP.IpAddresses.Protocol.ipv4);
         return pool;
     }
 
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializerTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializerTest.java
index 10e3592e548..8b9d60aeaf4 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializerTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/persistence/NodeSerializerTest.java
@@ -21,6 +21,7 @@ import com.yahoo.test.ManualClock;
 import com.yahoo.text.Utf8;
 import com.yahoo.vespa.hosted.provision.Node;
 import com.yahoo.vespa.hosted.provision.Node.State;
+import com.yahoo.vespa.hosted.provision.node.Address;
 import com.yahoo.vespa.hosted.provision.node.Agent;
 import com.yahoo.vespa.hosted.provision.node.Generation;
 import com.yahoo.vespa.hosted.provision.node.History;
@@ -249,15 +250,19 @@ public class NodeSerializerTest {
     public void serialize_ip_address_pool() {
         Node node = createNode();
 
-        // Test round-trip with IP address pool
-        node = node.with(node.ipConfig().with(IP.Pool.of(Set.of("::1", "::2", "::3"))));
+        // Test round-trip with address pool
+        node = node.with(node.ipConfig().withPool(IP.Pool.of(
+                Set.of("::1", "::2", "::3"),
+                List.of(new Address("a"), new Address("b"), new Address("c")))));
         Node copy = nodeSerializer.fromJson(node.state(), nodeSerializer.toJson(node));
-        assertEquals(node.ipConfig().pool().asSet(), copy.ipConfig().pool().asSet());
+        assertEquals(node.ipConfig().pool().getIpSet(), copy.ipConfig().pool().getIpSet());
+        assertEquals(Set.copyOf(node.ipConfig().pool().getAddressList()), Set.copyOf(copy.ipConfig().pool().getAddressList()));
 
-        // Test round-trip without IP address pool (handle empty pool)
+        // Test round-trip without address pool (handle empty pool)
         node = createNode();
         copy = nodeSerializer.fromJson(node.state(), nodeSerializer.toJson(node));
-        assertEquals(node.ipConfig().pool().asSet(), copy.ipConfig().pool().asSet());
+        assertEquals(node.ipConfig().pool().getIpSet(), copy.ipConfig().pool().getIpSet());
+        assertEquals(Set.copyOf(node.ipConfig().pool().getAddressList()), Set.copyOf(copy.ipConfig().pool().getAddressList()));
     }
 
     @Test
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/AllocationSimulator.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/AllocationSimulator.java
index b76588b7036..b59ef458d25 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/AllocationSimulator.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/AllocationSimulator.java
@@ -11,8 +11,9 @@ import com.yahoo.vespa.hosted.provision.Node;
 import com.yahoo.vespa.hosted.provision.NodeList;
 import com.yahoo.vespa.hosted.provision.node.Allocation;
 import com.yahoo.vespa.hosted.provision.node.Generation;
+import com.yahoo.vespa.hosted.provision.node.IP;
 
-import javax.swing.JFrame;
+import javax.swing.*;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
@@ -76,7 +77,7 @@ public class AllocationSimulator {
         Node.Builder builder = Node.create("fake", hostname, flavor,
                 parent.isPresent() ? Node.State.ready : Node.State.active,
                 parent.isPresent() ? NodeType.tenant : NodeType.host)
-                .ipConfig(Set.of("127.0.0.1"), parent.isPresent() ? Set.of() : getAdditionalIP());
+                .ipConfig(IP.Config.of(Set.of("127.0.0.1"), parent.isPresent() ? Set.of() : getAdditionalIP(), List.of()));
         parent.ifPresent(builder::parentHostname);
         allocation(tenant, flavor).ifPresent(builder::allocation);
 
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/HostCapacityTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/HostCapacityTest.java
index 4891387e9e8..c6e89680e85 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/HostCapacityTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/HostCapacityTest.java
@@ -43,9 +43,9 @@ public class HostCapacityTest {
         NodeFlavors nodeFlavors = FlavorConfigBuilder.createDummies("host", "docker", "docker2");
 
         // Create three docker hosts
-        host1 = Node.create("host1", new IP.Config(Set.of("::1"), generateIPs(2, 4)), "host1", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
-        host2 = Node.create("host2", new IP.Config(Set.of("::11"), generateIPs(12, 3)), "host2", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
-        host3 = Node.create("host3", new IP.Config(Set.of("::21"), generateIPs(22, 1)), "host3", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
+        host1 = Node.create("host1", IP.Config.of(Set.of("::1"), generateIPs(2, 4), List.of()), "host1", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
+        host2 = Node.create("host2", IP.Config.of(Set.of("::11"), generateIPs(12, 3), List.of()), "host2", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
+        host3 = Node.create("host3", IP.Config.of(Set.of("::21"), generateIPs(22, 1), List.of()), "host3", nodeFlavors.getFlavorOrThrow("host"), NodeType.host).build();
 
         // Add two containers to host1
         var nodeA = Node.createDockerNode(Set.of("::2"), "nodeA", "host1", resources1, NodeType.tenant).build();
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/LoadBalancerProvisionerTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/LoadBalancerProvisionerTest.java
index fe1fb43dcb9..c51ef7250e2 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/LoadBalancerProvisionerTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/LoadBalancerProvisionerTest.java
@@ -256,7 +256,7 @@ public class LoadBalancerProvisionerTest {
     private void assignIps(List<Node> nodes) {
         try (var lock = tester.nodeRepository().lockUnallocated()) {
             for (int i = 0; i < nodes.size(); i++) {
-                tester.nodeRepository().write(nodes.get(i).with(IP.Config.EMPTY.with(Set.of("127.0.0." + i))), lock);
+                tester.nodeRepository().write(nodes.get(i).with(IP.Config.EMPTY.withPrimary(Set.of("127.0.0." + i))), lock);
             }
         }
     }
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/NodeCandidateTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/NodeCandidateTest.java
index 7f637ba8804..8aa362aa932 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/NodeCandidateTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/NodeCandidateTest.java
@@ -133,7 +133,7 @@ public class NodeCandidateTest {
 
     private static Node node(String hostname, Node.State state) {
         return Node.create(hostname, hostname, new Flavor(new NodeResources(2, 2, 2, 2)), state, NodeType.tenant)
-                .ipConfig(Set.of("::1"), Set.of()).build();
+                .ipConfigWithEmptyPool(Set.of("::1")).build();
     }
 
     private static NodeCandidate node(String hostname,
@@ -143,9 +143,9 @@ public class NodeCandidateTest {
                                       boolean exclusiveSwitch) {
         Node node = Node.create(hostname, hostname, new Flavor(nodeResources), Node.State.ready, NodeType.tenant)
                 .parentHostname(hostname + "parent")
-                .ipConfig(Set.of("::1"), Set.of()).build();
+                .ipConfigWithEmptyPool(Set.of("::1")).build();
         Node parent = Node.create(hostname + "parent", hostname, new Flavor(totalHostResources), Node.State.ready, NodeType.host)
-                .ipConfig(Set.of("::1"), Set.of()).build();
+                .ipConfigWithEmptyPool(Set.of("::1")).build();
         return new NodeCandidate.ConcreteNodeCandidate(node, totalHostResources.subtract(allocatedHostResources), Optional.of(parent),
                                                        false, exclusiveSwitch, false, true, false);
     }
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/ProvisioningTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/ProvisioningTest.java
index 82b20bcae14..2fe39780cf5 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/ProvisioningTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/provisioning/ProvisioningTest.java
@@ -894,7 +894,7 @@ public class ProvisioningTest {
         Flavor flavor = tester.nodeRepository().flavors().getFlavorOrThrow("default");
         List<Node> nodes = List.of(
                 Node.create("cfghost1", new IP.Config(Set.of("::1:0"), Set.of("::1:1")), "cfghost1", flavor, NodeType.confighost).build(),
-                Node.create("cfghost2", new IP.Config(Set.of("::2:0"), Set.of("::2:1")), "cfghost2", flavor, NodeType.confighost).ipConfig(Set.of("::2:0"), Set.of("::2:1")).build(),
+                Node.create("cfghost2", new IP.Config(Set.of("::2:0"), Set.of("::2:1")), "cfghost2", flavor, NodeType.confighost).ipConfig(IP.Config.of(Set.of("::2:0"), Set.of("::2:1"), List.of())).build(),
                 Node.create("cfg1", new IP.Config(Set.of("::1:1"), Set.of()), "cfg1", flavor, NodeType.config).parentHostname("cfghost1").build(),
                 Node.create("cfg2", new IP.Config(Set.of("::2:1"), Set.of()), "cfg2", flavor, NodeType.config).parentHostname("cfghost2").build());
         tester.nodeRepository().setReady(tester.nodeRepository().addNodes(nodes, Agent.system), Agent.system, ProvisioningTest.class.getSimpleName());
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiTest.java b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiTest.java
index 97f850102fc..a98d383e219 100644
--- a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiTest.java
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/NodesV2ApiTest.java
@@ -360,6 +360,23 @@ public class NodesV2ApiTest {
     }
 
     @Test
+    public void patch_hostnames() throws IOException {
+        assertFile(new Request("http://localhost:8080/nodes/v2/node/host4.yahoo.com"), "node4.json");
+
+        assertResponse(new Request("http://localhost:8080/nodes/v2/node/host4.yahoo.com",
+                        Utf8.toBytes("{\"additionalHostnames\": [\"a\",\"b\"]}"), Request.Method.PATCH),
+                "{\"message\":\"Updated host4.yahoo.com\"}");
+
+        assertFile(new Request("http://localhost:8080/nodes/v2/node/host4.yahoo.com"), "node4-with-hostnames.json");
+
+        assertResponse(new Request("http://localhost:8080/nodes/v2/node/host4.yahoo.com",
+                        Utf8.toBytes("{\"additionalHostnames\": []}"), Request.Method.PATCH),
+                "{\"message\":\"Updated host4.yahoo.com\"}");
+
+        assertFile(new Request("http://localhost:8080/nodes/v2/node/host4.yahoo.com"), "node4.json");
+    }
+
+    @Test
     public void post_controller_node() throws Exception {
         String data = "[{\"hostname\":\"controller1.yahoo.com\", \"openStackId\":\"fake-controller1.yahoo.com\"," +
                       createIpAddresses("127.0.0.1") +
diff --git a/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/responses/node4-with-hostnames.json b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/responses/node4-with-hostnames.json
new file mode 100644
index 00000000000..40b5f29c13f
--- /dev/null
+++ b/node-repository/src/test/java/com/yahoo/vespa/hosted/provision/restapi/responses/node4-with-hostnames.json
@@ -0,0 +1,65 @@
+{
+  "url": "http://localhost:8080/nodes/v2/node/host4.yahoo.com",
+  "id": "host4.yahoo.com",
+  "state": "active",
+  "type": "tenant",
+  "hostname": "host4.yahoo.com",
+  "parentHostname": "dockerhost1.yahoo.com",
+  "openStackId": "node4",
+  "flavor": "[vcpu: 1.0, memory: 4.0 Gb, disk 100.0 Gb, bandwidth: 1.0 Gbps, storage type: local]",
+  "resources":{"vcpu":1.0,"memoryGb":4.0,"diskGb":100.0,"bandwidthGbps":1.0,"diskSpeed":"fast","storageType":"local"},
+  "environment": "DOCKER_CONTAINER",
+  "owner": {
+    "tenant": "tenant3",
+    "application": "application3",
+    "instance": "instance3"
+  },
+  "membership": {
+    "clustertype": "content",
+    "clusterid": "id3",
+    "group": "0",
+    "index": 0,
+    "retired": false
+  },
+  "restartGeneration": 0,
+  "currentRestartGeneration": 0,
+  "wantedDockerImage": "docker-registry.domain.tld:8080/dist/vespa:6.42.0",
+  "wantedVespaVersion": "6.42.0",
+  "requestedResources": { "vcpu":1.0, "memoryGb":4.0, "diskGb":100.0, "bandwidthGbps":1.0, "diskSpeed":"fast", "storageType":"any" },
+  "allowedToBeDown": false,
+  "rebootGeneration": 1,
+  "currentRebootGeneration": 0,
+  "vespaVersion": "6.41.0",
+  "currentDockerImage": "docker-registry.domain.tld:8080/dist/vespa:6.41.0",
+  "failCount": 0,
+  "wantToRetire": false,
+  "wantToDeprovision": false,
+  "history": [
+    {
+      "event": "provisioned",
+      "at": 123,
+      "agent": "system"
+    },
+    {
+      "event": "readied",
+      "at": 123,
+      "agent": "system"
+    },
+    {
+      "event": "reserved",
+      "at": 123,
+      "agent": "application"
+    },
+    {
+      "event": "activated",
+      "at": 123,
+      "agent": "application"
+    }
+  ],
+  "ipAddresses": [
+    "127.0.4.1",
+    "::4:1"
+  ],
+  "additionalIpAddresses": [],
+  "additionalHostnames": ["a","b"]
+}