Add projectsDelta method to ClusterChangedEvent (#127697)

Similar to nodesDelta, the projectsDelta provides a centrailzed method
to tell the added and removed projects so that cluster
listeners/appliers do not need to compute it individually.

Note the delta currently does not have updated. This needs to wait till
we stop eagerly creating ProjectMetadata.Builder in Metadata.Builder.

Author: ywangd

server/src/main/java/org/elasticsearch/cluster/ClusterChangedEvent.java

@@ -13,9 +13,11 @@
 import org.elasticsearch.cluster.metadata.IndexGraveyard.IndexGraveyardDiff;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
+import org.elasticsearch.cluster.metadata.ProjectId;
 import org.elasticsearch.cluster.metadata.ProjectMetadata;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.IndexRoutingTable;
+import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.gateway.GatewayService;
 import org.elasticsearch.index.Index;
 
@@ -41,6 +43,8 @@ public class ClusterChangedEvent {
 
     private final DiscoveryNodes.Delta nodesDelta;
 
+    private final ProjectsDelta projectsDelta;
+
     public ClusterChangedEvent(String source, ClusterState state, ClusterState previousState) {
         Objects.requireNonNull(source, "source must not be null");
         Objects.requireNonNull(state, "state must not be null");
@@ -49,6 +53,7 @@ public ClusterChangedEvent(String source, ClusterState state, ClusterState previ
         this.state = state;
         this.previousState = previousState;
         this.nodesDelta = state.nodes().delta(previousState.nodes());
+        this.projectsDelta = calculateProjectDelta(previousState.metadata(), state.metadata());
     }
 
     /**
@@ -237,6 +242,13 @@ public boolean nodesChanged() {
         return nodesRemoved() || nodesAdded();
     }
 
+    /**
+     * Returns the {@link ProjectsDelta} between the previous cluster state and the new cluster state.
+     */
+    public ProjectsDelta projectDelta() {
+        return projectsDelta;
+    }
+
     /**
      * Determines whether or not the current cluster state represents an entirely
      * new cluster, either when a node joins a cluster for the first time or when
@@ -336,4 +348,32 @@ private List<Index> indicesDeletedFromTombstones() {
             .toList();
     }
 
+    private static ProjectsDelta calculateProjectDelta(Metadata previousMetadata, Metadata currentMetadata) {
+        if (previousMetadata == currentMetadata
+            || (previousMetadata.projects().size() == 1
+                && previousMetadata.hasProject(ProjectId.DEFAULT)
+                && currentMetadata.projects().size() == 1
+                && currentMetadata.hasProject(ProjectId.DEFAULT))) {
+            return ProjectsDelta.EMPTY;
+        }
+
+        final Set<ProjectId> added = Collections.unmodifiableSet(
+            Sets.difference(currentMetadata.projects().keySet(), previousMetadata.projects().keySet())
+        );
+        final Set<ProjectId> removed = Collections.unmodifiableSet(
+            Sets.difference(previousMetadata.projects().keySet(), currentMetadata.projects().keySet())
+        );
+        // TODO: Enable the following assertions once tests no longer add or remove default projects
+        // assert added.contains(ProjectId.DEFAULT) == false;
+        // assert removed.contains(ProjectId.DEFAULT) == false;
+        return new ProjectsDelta(added, removed);
+    }
+
+    public record ProjectsDelta(Set<ProjectId> added, Set<ProjectId> removed) {
+        private static final ProjectsDelta EMPTY = new ProjectsDelta(Set.of(), Set.of());
+
+        public boolean isEmpty() {
+            return added.isEmpty() && removed.isEmpty();
+        }
+    }
 }

server/src/test/java/org/elasticsearch/cluster/ClusterChangedEventTests.java

@@ -14,7 +14,9 @@
 import org.elasticsearch.cluster.metadata.IndexGraveyard;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
+import org.elasticsearch.cluster.metadata.ProjectId;
 import org.elasticsearch.cluster.metadata.ProjectMetadata;
+import org.elasticsearch.cluster.metadata.ReservedStateMetadata;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodeRole;
 import org.elasticsearch.cluster.node.DiscoveryNodeUtils;
@@ -520,6 +522,65 @@ public void testChangedCustomMetadataSetMultiProject() {
         assertEquals(Set.of(IndexGraveyard.TYPE, project2Custom.getWriteableName()), event.changedCustomProjectMetadataSet());
     }
 
+    public void testProjectsDelta() {
+        final var state0 = ClusterState.builder(TEST_CLUSTER_NAME).build();
+
+        // No project changes
+        final var state1 = ClusterState.builder(state0)
+            .metadata(Metadata.builder(state0.metadata()).put(ReservedStateMetadata.builder("test").build()))
+            .build();
+        ClusterChangedEvent event = new ClusterChangedEvent("test", state1, state0);
+        assertTrue(event.projectDelta().isEmpty());
+
+        // Add projects
+        final List<ProjectId> projectIds = randomList(1, 5, ESTestCase::randomUniqueProjectId);
+        Metadata.Builder metadataBuilder = Metadata.builder(state1.metadata());
+        for (ProjectId projectId : projectIds) {
+            metadataBuilder.put(ProjectMetadata.builder(projectId));
+        }
+        final var state2 = ClusterState.builder(state1).metadata(metadataBuilder.build()).build();
+        event = new ClusterChangedEvent("test", state2, state1);
+        assertThat(event.projectDelta().added(), containsInAnyOrder(projectIds.toArray()));
+        assertThat(event.projectDelta().removed(), empty());
+
+        // Add more projects and delete one
+        final var removedProjectIds = randomNonEmptySubsetOf(projectIds);
+        final List<ProjectId> moreProjectIds = randomList(1, 3, ESTestCase::randomUniqueProjectId);
+        metadataBuilder = Metadata.builder(state2.metadata());
+        GlobalRoutingTable.Builder routingTableBuilder = GlobalRoutingTable.builder(state2.globalRoutingTable());
+        for (ProjectId projectId : removedProjectIds) {
+            metadataBuilder.removeProject(projectId);
+            routingTableBuilder.removeProject(projectId);
+        }
+        for (ProjectId projectId : moreProjectIds) {
+            metadataBuilder.put(ProjectMetadata.builder(projectId));
+        }
+
+        final var state3 = ClusterState.builder(state2).metadata(metadataBuilder.build()).routingTable(routingTableBuilder.build()).build();
+
+        event = new ClusterChangedEvent("test", state3, state2);
+        assertThat(event.projectDelta().added(), containsInAnyOrder(moreProjectIds.toArray()));
+        assertThat(event.projectDelta().removed(), containsInAnyOrder(removedProjectIds.toArray()));
+
+        // Remove all projects
+        final List<ProjectId> remainingProjects = state3.metadata()
+            .projects()
+            .keySet()
+            .stream()
+            .filter(projectId -> ProjectId.DEFAULT.equals(projectId) == false)
+            .toList();
+        metadataBuilder = Metadata.builder(state3.metadata());
+        routingTableBuilder = GlobalRoutingTable.builder(state3.globalRoutingTable());
+        for (ProjectId projectId : remainingProjects) {
+            metadataBuilder.removeProject(projectId);
+            routingTableBuilder.removeProject(projectId);
+        }
+        final var state4 = ClusterState.builder(state3).metadata(metadataBuilder.build()).routingTable(routingTableBuilder.build()).build();
+        event = new ClusterChangedEvent("test", state4, state3);
+        assertThat(event.projectDelta().added(), empty());
+        assertThat(event.projectDelta().removed(), containsInAnyOrder(remainingProjects.toArray()));
+    }
+
     private static class CustomClusterMetadata2 extends TestClusterCustomMetadata {
         protected CustomClusterMetadata2(String data) {
             super(data);

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/inference/persistence/TrainedModelCacheMetadataServiceTests.java

@@ -74,6 +74,7 @@ public void testRefreshCacheVersionOnMasterNode() {
         ClusterState clusterState = mock(ClusterState.class);
         when(clusterState.clusterRecovered()).thenReturn(true);
         when(clusterState.nodes()).thenReturn(clusterNodes);
+        when(clusterState.metadata()).thenReturn(Metadata.EMPTY_METADATA);
 
         modelCacheMetadataService.clusterChanged(new ClusterChangedEvent("test", clusterState, ClusterState.EMPTY_STATE));
 

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/support/QueryableBuiltInRolesSynchronizerTests.java

@@ -330,8 +330,8 @@ public void testSecurityIndexDeleted() {
 
         synchronizer.clusterChanged(event(currentClusterState, previousClusterState));
 
-        verify(previousClusterState, times(1)).metadata();
-        verify(currentClusterState, times(1)).metadata();
+        verify(previousClusterState, times(2)).metadata();
+        verify(currentClusterState, times(2)).metadata();
         verifyNoMoreInteractions(nativeRolesStore, featureService, taskQueue, reservedRolesProvider, threadPool, clusterService);
     }