Support lower bound on number of shared hosts

Adds a 'minCount' field to the shared host jackson flag, denoting the minimum
number of "shared hosts" that must exist, otherwise the deficit will be
provisioned by DynamicProvisioningMaintainer.

A "shared host" is one that is considered for allocation if current tenant node
allocations were removed: It must be a tenant host, cannot be an exclusiveTo
host, etc.

minCount requires the setting of (at least one) shared host.

3 files changed, 67 insertions, 7 deletions

diff --git a/flags/src/main/java/com/yahoo/vespa/flags/custom/SharedHost.java b/flags/src/main/java/com/yahoo/vespa/flags/custom/SharedHost.java
index e463159eb8f..ab9127ebfe4 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/custom/SharedHost.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/custom/SharedHost.java
@@ -2,6 +2,7 @@
 package com.yahoo.vespa.flags.custom;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonGetter;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import com.fasterxml.jackson.annotation.JsonInclude;
@@ -19,29 +20,50 @@ import java.util.Objects;
 @JsonIgnoreProperties(ignoreUnknown = true)
 @JsonInclude(value = JsonInclude.Include.NON_NULL)
 public class SharedHost {
+    private final int DEFAULT_MIN_COUNT = 0;
+
     private final List<HostResources> resources;
+    private final int minCount;
 
     public static SharedHost createDisabled() {
-        return new SharedHost(null);
+        return new SharedHost(null, null);
     }
 
+    /**
+     * @param resourcesOrNull the resources of the shared host (or several to support e.g. tiers or
+     *                        fast/slow disks separately)
+     * @param minCountOrNull  the minimum number of shared hosts
+     */
     @JsonCreator
-    public SharedHost(@JsonProperty("resources") List<HostResources> resources) {
-        this.resources = resources == null ? List.of() : List.copyOf(resources);
+    public SharedHost(@JsonProperty("resources") List<HostResources> resourcesOrNull,
+                      @JsonProperty("min-count") Integer minCountOrNull) {
+        this.resources = resourcesOrNull == null ? List.of() : List.copyOf(resourcesOrNull);
+        this.minCount = requireNonNegative(minCountOrNull, DEFAULT_MIN_COUNT, "min-count");
     }
 
-    @JsonProperty("resources")
+    @JsonGetter("resources")
     public List<HostResources> getResourcesOrNull() {
         return resources.isEmpty() ? null : resources;
     }
 
+    @JsonGetter("min-count")
+    public Integer getMinCountOrNull() {
+        return minCount == DEFAULT_MIN_COUNT ? null : minCount;
+    }
+
+    @JsonIgnore
+    public boolean isEnabled() {
+        return resources.size() > 0;
+    }
+
     @JsonIgnore
     public List<HostResources> getHostResources() {
         return resources;
     }
 
-    public boolean isEnabled() {
-        return resources.size() > 0;
+    @JsonIgnore
+    public int getMinCount() {
+        return minCount;
     }
 
     @Override
@@ -61,4 +83,16 @@ public class SharedHost {
     public int hashCode() {
         return Objects.hash(resources);
     }
+
+    private int requireNonNegative(Integer integerOrNull, int defaultValue, String fieldName) {
+        if (integerOrNull == null) {
+            return defaultValue;
+        }
+
+        if (integerOrNull < 0) {
+            throw new IllegalArgumentException(fieldName + " cannot be negative");
+        }
+
+        return integerOrNull;
+    }
 }
diff --git a/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java b/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
index 636eea2c33c..6b043ea5a89 100644
--- a/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
+++ b/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
@@ -114,7 +114,8 @@ public class FlagsTest {
         SharedHost sharedHost = new SharedHost(List.of(new HostResources(
                 4.0, 16.0, 50.0, 0.3,
                 "fast", "local",
-                10)));
+                10)),
+                null);
         testGeneric(Flags.SHARED_HOST, sharedHost);
     }
 
diff --git a/flags/src/test/java/com/yahoo/vespa/flags/custom/SharedHostTest.java b/flags/src/test/java/com/yahoo/vespa/flags/custom/SharedHostTest.java
new file mode 100644
index 00000000000..f0a11f244a4
--- /dev/null
+++ b/flags/src/test/java/com/yahoo/vespa/flags/custom/SharedHostTest.java
@@ -0,0 +1,25 @@
+// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags.custom;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class SharedHostTest {
+    @Test
+    public void serialization() throws IOException {
+        verifySerialization(new SharedHost(List.of(new HostResources(1.0, 2.0, 3.0, 4.0, "fast", "remote", 5)), 6));
+        verifySerialization(new SharedHost(List.of(new HostResources(1.0, 2.0, 3.0, 4.0, "fast", "remote", 5)), null));
+    }
+
+    private void verifySerialization(SharedHost sharedHost) throws IOException {
+        ObjectMapper mapper = new ObjectMapper();
+        String json = mapper.writeValueAsString(sharedHost);
+        SharedHost deserialized = mapper.readValue(json, SharedHost.class);
+        assertEquals(sharedHost, deserialized);
+    }
+}
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