[ML] Don't install empty ML metadata on startup (#30751)

This change is to support rolling upgrade from a pre-6.3 default
distribution (i.e. without X-Pack) to a 6.3+ default distribution
(i.e. with X-Pack).

The ML metadata is no longer eagerly added to the cluster state
as soon as the master node has X-Pack available.  Instead, it
is added when the first ML job is created.

As a result all methods that get the ML metadata need to be able
to handle the situation where there is no ML metadata in the
current cluster state.  They do this by behaving as though an
empty ML metadata was present.  This logic is encapsulated by
always asking for the current ML metadata using a static method
on the MlMetadata class.

Relates #30731

Author: David Roberts

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/MlMetadata.java

@@ -9,6 +9,7 @@
 import org.elasticsearch.ResourceNotFoundException;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.AbstractDiffable;
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.cluster.DiffableUtils;
 import org.elasticsearch.cluster.NamedDiff;
@@ -467,6 +468,14 @@ public static DatafeedState getDatafeedState(String datafeedId, @Nullable Persis
         }
     }
 
+    public static MlMetadata getMlMetadata(ClusterState state) {
+        MlMetadata mlMetadata = (state == null) ? null : state.getMetaData().custom(MLMetadataField.TYPE);
+        if (mlMetadata == null) {
+            return EMPTY_METADATA;
+        }
+        return mlMetadata;
+    }
+
     public static class JobAlreadyMarkedAsDeletedException extends RuntimeException {
     }
 }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/persistence/AnomalyDetectorsIndex.java

@@ -6,7 +6,6 @@
 package org.elasticsearch.xpack.core.ml.job.persistence;
 
 import org.elasticsearch.cluster.ClusterState;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 
 /**
@@ -47,8 +46,7 @@ public static String resultsWriteAlias(String jobId) {
      * @return The index name
      */
     public static String getPhysicalIndexFromState(ClusterState state, String jobId) {
-        MlMetadata meta = state.getMetaData().custom(MLMetadataField.TYPE);
-        return meta.getJobs().get(jobId).getResultsIndexName();
+        return MlMetadata.getMlMetadata(state).getJobs().get(jobId).getResultsIndexName();
     }
 
     /**

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MachineLearningFeatureSet.java

@@ -23,7 +23,6 @@
 import org.elasticsearch.xpack.core.XPackPlugin;
 import org.elasticsearch.xpack.core.XPackSettings;
 import org.elasticsearch.xpack.core.XPackField;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
 import org.elasticsearch.xpack.core.ml.MachineLearningFeatureSetUsage;
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 import org.elasticsearch.xpack.core.ml.action.GetDatafeedsStatsAction;
@@ -132,15 +131,7 @@ public Map<String, Object> nativeCodeInfo() {
     @Override
     public void usage(ActionListener<XPackFeatureSet.Usage> listener) {
         ClusterState state = clusterService.state();
-        MlMetadata mlMetadata = state.getMetaData().custom(MLMetadataField.TYPE);
-
-        // Handle case when usage is called but MlMetadata has not been installed yet
-        if (mlMetadata == null) {
-            listener.onResponse(new MachineLearningFeatureSetUsage(available(), enabled,
-                    Collections.emptyMap(), Collections.emptyMap()));
-        } else {
-            new Retriever(client, mlMetadata, available(), enabled()).execute(listener);
-        }
+        new Retriever(client, MlMetadata.getMlMetadata(state), available(), enabled()).execute(listener);
     }
 
     public static class Retriever {

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlAssignmentNotifier.java

@@ -13,7 +13,6 @@
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.threadpool.ThreadPool;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 import org.elasticsearch.xpack.core.ml.action.OpenJobAction;
 import org.elasticsearch.xpack.core.ml.action.StartDatafeedAction;
@@ -90,8 +89,7 @@ public void clusterChanged(ClusterChangedEvent event) {
                 }
             } else if (StartDatafeedAction.TASK_NAME.equals(currentTask.getTaskName())) {
                 String datafeedId = ((StartDatafeedAction.DatafeedParams) currentTask.getParams()).getDatafeedId();
-                MlMetadata mlMetadata = event.state().getMetaData().custom(MLMetadataField.TYPE);
-                DatafeedConfig datafeedConfig = mlMetadata.getDatafeed(datafeedId);
+                DatafeedConfig datafeedConfig = MlMetadata.getMlMetadata(event.state()).getDatafeed(datafeedId);
                 if (currentAssignment.getExecutorNode() == null) {
                     String msg = "No node found to start datafeed [" + datafeedId +"]. Reasons [" +
                             currentAssignment.getExplanation() + "]";

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlInitializationService.java

@@ -7,29 +7,20 @@
 
 import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.ClusterChangedEvent;
-import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ClusterStateListener;
-import org.elasticsearch.cluster.ClusterStateUpdateTask;
-import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.component.LifecycleListener;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.gateway.GatewayService;
 import org.elasticsearch.threadpool.ThreadPool;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
-import org.elasticsearch.xpack.core.ml.MlMetadata;
-
-import java.util.concurrent.atomic.AtomicBoolean;
 
 class MlInitializationService extends AbstractComponent implements ClusterStateListener {
 
     private final ThreadPool threadPool;
     private final ClusterService clusterService;
     private final Client client;
 
-    private final AtomicBoolean installMlMetadataCheck = new AtomicBoolean(false);
-
     private volatile MlDailyMaintenanceService mlDailyMaintenanceService;
 
     MlInitializationService(Settings settings, ThreadPool threadPool, ClusterService clusterService, Client client) {
@@ -48,45 +39,12 @@ public void clusterChanged(ClusterChangedEvent event) {
         }
 
         if (event.localNodeMaster()) {
-            MetaData metaData = event.state().metaData();
-            installMlMetadata(metaData);
             installDailyMaintenanceService();
         } else {
             uninstallDailyMaintenanceService();
         }
     }
 
-    private void installMlMetadata(MetaData metaData) {
-        if (metaData.custom(MLMetadataField.TYPE) == null) {
-            if (installMlMetadataCheck.compareAndSet(false, true)) {
-                threadPool.executor(ThreadPool.Names.GENERIC).execute(() ->
-                    clusterService.submitStateUpdateTask("install-ml-metadata", new ClusterStateUpdateTask() {
-                        @Override
-                        public ClusterState execute(ClusterState currentState) throws Exception {
-                            // If the metadata has been added already don't try to update
-                            if (currentState.metaData().custom(MLMetadataField.TYPE) != null) {
-                                return currentState;
-                            }
-                            ClusterState.Builder builder = new ClusterState.Builder(currentState);
-                            MetaData.Builder metadataBuilder = MetaData.builder(currentState.metaData());
-                            metadataBuilder.putCustom(MLMetadataField.TYPE, MlMetadata.EMPTY_METADATA);
-                            builder.metaData(metadataBuilder.build());
-                            return builder.build();
-                        }
-
-                        @Override
-                        public void onFailure(String source, Exception e) {
-                            installMlMetadataCheck.set(false);
-                            logger.error("unable to install ml metadata", e);
-                        }
-                    })
-                );
-            }
-        } else {
-            installMlMetadataCheck.set(false);
-        }
-    }
-
     private void installDailyMaintenanceService() {
         if (mlDailyMaintenanceService == null) {
             mlDailyMaintenanceService = new MlDailyMaintenanceService(clusterService.getClusterName(), threadPool, client);

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportCloseJobAction.java

@@ -27,7 +27,6 @@
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 import org.elasticsearch.xpack.core.ml.action.CloseJobAction;
 import org.elasticsearch.xpack.core.ml.action.FinalizeJobExecutionAction;
@@ -92,8 +91,7 @@ public TransportCloseJobAction(Settings settings, TransportService transportServ
     static void resolveAndValidateJobId(CloseJobAction.Request request, ClusterState state, List<String> openJobIds,
                                         List<String> closingJobIds) {
         PersistentTasksCustomMetaData tasksMetaData = state.getMetaData().custom(PersistentTasksCustomMetaData.TYPE);
-        MlMetadata maybeNull = state.metaData().custom(MLMetadataField.TYPE);
-        final MlMetadata mlMetadata = (maybeNull == null) ? MlMetadata.EMPTY_METADATA : maybeNull;
+        final MlMetadata mlMetadata = MlMetadata.getMlMetadata(state);
 
         List<String> failedJobs = new ArrayList<>();
 
@@ -107,7 +105,7 @@ static void resolveAndValidateJobId(CloseJobAction.Request request, ClusterState
         };
 
         Set<String> expandedJobIds = mlMetadata.expandJobIds(request.getJobId(), request.allowNoJobs());
-        expandedJobIds.stream().forEach(jobIdProcessor::accept);
+        expandedJobIds.forEach(jobIdProcessor::accept);
         if (request.isForce() == false && failedJobs.size() > 0) {
             if (expandedJobIds.size() == 1) {
                 throw ExceptionsHelper.conflictStatusException("cannot close job [{}] because it failed, use force close",

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteDatafeedAction.java

@@ -119,8 +119,8 @@ protected DeleteDatafeedAction.Response newResponse(boolean acknowledged) {
                     }
 
                     @Override
-                    public ClusterState execute(ClusterState currentState) throws Exception {
-                        MlMetadata currentMetadata = currentState.getMetaData().custom(MLMetadataField.TYPE);
+                    public ClusterState execute(ClusterState currentState) {
+                        MlMetadata currentMetadata = MlMetadata.getMlMetadata(currentState);
                         PersistentTasksCustomMetaData persistentTasks =
                                 currentState.getMetaData().custom(PersistentTasksCustomMetaData.TYPE);
                         MlMetadata newMetadata = new MlMetadata.Builder(currentMetadata)

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteFilterAction.java

@@ -24,7 +24,6 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 import org.elasticsearch.xpack.core.ml.action.DeleteFilterAction;
-import org.elasticsearch.xpack.core.ml.MLMetadataField;
 import org.elasticsearch.xpack.core.ml.MlMetaIndex;
 import org.elasticsearch.xpack.core.ml.MlMetadata;
 import org.elasticsearch.xpack.core.ml.job.config.Detector;
@@ -60,8 +59,7 @@ protected void doExecute(DeleteFilterAction.Request request, ActionListener<Dele
 
         final String filterId = request.getFilterId();
         ClusterState state = clusterService.state();
-        MlMetadata currentMlMetadata = state.metaData().custom(MLMetadataField.TYPE);
-        Map<String, Job> jobs = currentMlMetadata.getJobs();
+        Map<String, Job> jobs = MlMetadata.getMlMetadata(state).getJobs();
         List<String> currentlyUsedBy = new ArrayList<>();
         for (Job job : jobs.values()) {
             List<Detector> detectors = job.getAnalysisConfig().getDetectors();

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportDeleteJobAction.java

@@ -200,10 +200,9 @@ public void onFailure(Exception e) {
     void markJobAsDeleting(String jobId, ActionListener<Boolean> listener, boolean force) {
         clusterService.submitStateUpdateTask("mark-job-as-deleted", new ClusterStateUpdateTask() {
             @Override
-            public ClusterState execute(ClusterState currentState) throws Exception {
-                MlMetadata currentMlMetadata = currentState.metaData().custom(MLMetadataField.TYPE);
+            public ClusterState execute(ClusterState currentState) {
                 PersistentTasksCustomMetaData tasks = currentState.metaData().custom(PersistentTasksCustomMetaData.TYPE);
-                MlMetadata.Builder builder = new MlMetadata.Builder(currentMlMetadata);
+                MlMetadata.Builder builder = new MlMetadata.Builder(MlMetadata.getMlMetadata(currentState));
                 builder.markJobAsDeleted(jobId, tasks, force);
                 return buildNewClusterState(currentState, builder);
             }
@@ -248,11 +247,7 @@ public void onTimeout(TimeValue timeout) {
     }
 
     static boolean jobIsDeletedFromState(String jobId, ClusterState clusterState) {
-        MlMetadata metadata = clusterState.metaData().custom(MLMetadataField.TYPE);
-        if (metadata == null) {
-            return true;
-        }
-        return !metadata.getJobs().containsKey(jobId);
+        return !MlMetadata.getMlMetadata(clusterState).getJobs().containsKey(jobId);
     }
 
     private static ClusterState buildNewClusterState(ClusterState currentState, MlMetadata.Builder builder) {

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportFinalizeJobExecutionAction.java

@@ -56,8 +56,8 @@ protected void masterOperation(FinalizeJobExecutionAction.Request request, Clust
         logger.debug("finalizing jobs [{}]", jobIdString);
         clusterService.submitStateUpdateTask(source, new ClusterStateUpdateTask() {
             @Override
-            public ClusterState execute(ClusterState currentState) throws Exception {
-                MlMetadata mlMetadata = currentState.metaData().custom(MLMetadataField.TYPE);
+            public ClusterState execute(ClusterState currentState) {
+                MlMetadata mlMetadata = MlMetadata.getMlMetadata(currentState);
                 MlMetadata.Builder mlMetadataBuilder = new MlMetadata.Builder(mlMetadata);
                 Date finishedTime = new Date();