Make IlmHealthIndicatorService work in multi-project cluster (#129961)

This does _not_ make the health indicator project-aware, it merely
avoids exceptions in case there are multiple projects in the cluster.
The health indicator would require significant refactoring to be made
project-aware, which is not worth it since ILM will not be running in a
multi-project context (i.e. serverless).

Author: nielsbauman

x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/ilm/IlmHealthIndicatorService.java

@@ -7,10 +7,14 @@
 
 package org.elasticsearch.xpack.ilm;
 
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.cluster.metadata.ProjectId;
+import org.elasticsearch.cluster.metadata.ProjectMetadata;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.core.NotMultiProjectCapable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.health.Diagnosis;
 import org.elasticsearch.health.HealthIndicatorDetails;
@@ -210,7 +214,7 @@ public String name() {
 
     @Override
     public HealthIndicatorResult calculate(boolean verbose, int maxAffectedResourcesCount, HealthInfo healthInfo) {
-        final var projectMetadata = clusterService.state().metadata().getProject();
+        final var projectMetadata = getDefaultILMProject(clusterService.state());
         var ilmMetadata = projectMetadata.custom(IndexLifecycleMetadata.TYPE, IndexLifecycleMetadata.EMPTY);
         final var currentMode = currentILMMode(projectMetadata);
         if (ilmMetadata.getPolicyMetadatas().isEmpty()) {
@@ -341,14 +345,13 @@ static class StagnatingIndicesFinder {
          * @return A list containing the ILM managed indices that are stagnated in any ILM action/step.
          */
         public List<IndexMetadata> find() {
-            var metadata = clusterService.state().metadata();
+            final var project = getDefaultILMProject(clusterService.state());
             var now = nowSupplier.getAsLong();
 
-            return metadata.getProject()
-                .indices()
+            return project.indices()
                 .values()
                 .stream()
-                .filter(metadata.getProject()::isIndexManagedByILM)
+                .filter(project::isIndexManagedByILM)
                 .filter(md -> isStagnated(rules, now, md))
                 .toList();
         }
@@ -496,4 +499,13 @@ public boolean test(Long now, IndexMetadata indexMetadata) {
                     || (maxRetries != null && failedStepRetryCount != null && failedStepRetryCount > maxRetries));
         }
     }
+
+    /**
+     * This method solely exists because we are not making ILM properly project-aware and it's not worth the investment of altering this
+     * health indicator to be project-aware.
+     */
+    @NotMultiProjectCapable
+    private static ProjectMetadata getDefaultILMProject(ClusterState state) {
+        return state.metadata().getProject(ProjectId.DEFAULT);
+    }
 }

x-pack/qa/multi-project/core-rest-tests-with-multiple-projects/build.gradle

@@ -52,7 +52,6 @@ tasks.named("yamlRestTest").configure {
     '^cluster.desired_balance/10_basic/*',
     '^cluster.stats/10_basic/snapshot stats reported in get cluster stats',
     '^data_stream/40_supported_apis/Verify shard stores api', // uses _shard_stores API
-    '^health/10_basic/*',
     '^indices.get_alias/10_basic/Get alias against closed indices', // Does NOT work with security enabled, see also core-rest-tests-with-security
     '^indices.recovery/*/*',
     '^indices.resolve_cluster/*/*',