Always re-run Feature migrations which have encountered errors (elast…

…ic#83918)

This PR addressed the behavior described in elastic#83917, in which Feature migrations
which have encountered errors are not re-run in some cases. As of this PR, Features
which have encountered errors during migration are treated the same as Features 
requiring migration.

This PR also adds a test which artificially replicates elastic#83917.

docs/changelog/83918.yaml

@@ -0,0 +1,6 @@
+pr: 83918
+summary: Always re-run Feature migrations which have encountered errors
+area: Infra/Core
+type: bug
+issues:
+ - 83917

modules/reindex/src/internalClusterTest/java/org/elasticsearch/migration/FeatureMigrationIT.java

@@ -25,6 +25,8 @@
 import org.elasticsearch.action.support.ActiveShardCount;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterStateTaskExecutor;
+import org.elasticsearch.cluster.ClusterStateUpdateTask;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.cluster.service.ClusterService;
@@ -37,6 +39,7 @@
 import org.elasticsearch.reindex.ReindexPlugin;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.upgrades.FeatureMigrationResults;
+import org.elasticsearch.upgrades.SingleFeatureMigrationResult;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentType;
 import org.elasticsearch.xcontent.json.JsonXContent;
@@ -51,6 +54,8 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BiConsumer;
 import java.util.function.Function;
@@ -268,6 +273,67 @@ public void testMigrateIndexWithWriteBlock() throws Exception {
         });
     }
 
+    public void testMigrationWillRunAfterError() throws Exception {
+        createSystemIndexForDescriptor(INTERNAL_MANAGED);
+
+        TestPlugin.preMigrationHook.set((state) -> Collections.emptyMap());
+        TestPlugin.postMigrationHook.set((state, metadata) -> {});
+
+        ensureGreen();
+
+        SetOnce<Exception> failure = new SetOnce<>();
+        CountDownLatch clusterStateUpdated = new CountDownLatch(1);
+        internalCluster().getCurrentMasterNodeInstance(ClusterService.class)
+            .submitStateUpdateTask(this.getTestName(), new ClusterStateUpdateTask() {
+                @Override
+                public ClusterState execute(ClusterState currentState) throws Exception {
+                    FeatureMigrationResults newResults = new FeatureMigrationResults(
+                        Collections.singletonMap(
+                            FEATURE_NAME,
+                            SingleFeatureMigrationResult.failure(INTERNAL_MANAGED_INDEX_NAME, new RuntimeException("it failed :("))
+                        )
+                    );
+                    Metadata newMetadata = Metadata.builder(currentState.metadata())
+                        .putCustom(FeatureMigrationResults.TYPE, newResults)
+                        .build();
+                    return ClusterState.builder(currentState).metadata(newMetadata).build();
+                }
+
+                @Override
+                public void clusterStateProcessed(ClusterState oldState, ClusterState newState) {
+                    clusterStateUpdated.countDown();
+                }
+
+                @Override
+                public void onFailure(Exception e) {
+                    failure.set(e);
+                    clusterStateUpdated.countDown();
+                }
+            }, ClusterStateTaskExecutor.unbatched());
+
+        clusterStateUpdated.await(10, TimeUnit.SECONDS); // Should be basically instantaneous
+        if (failure.get() != null) {
+            logger.error("cluster state update to inject migration failure state did not succeed", failure.get());
+            fail("cluster state update failed, see log for details");
+        }
+
+        PostFeatureUpgradeRequest migrationRequest = new PostFeatureUpgradeRequest();
+        PostFeatureUpgradeResponse migrationResponse = client().execute(PostFeatureUpgradeAction.INSTANCE, migrationRequest).get();
+        // Make sure we actually started the migration
+        assertTrue(
+            "could not find [" + FEATURE_NAME + "] in response: " + Strings.toString(migrationResponse),
+            migrationResponse.getFeatures().stream().anyMatch(feature -> feature.getFeatureName().equals(FEATURE_NAME))
+        );
+
+        // Now wait for the migration to finish (otherwise the test infra explodes)
+        assertBusy(() -> {
+            GetFeatureUpgradeStatusRequest getStatusRequest = new GetFeatureUpgradeStatusRequest();
+            GetFeatureUpgradeStatusResponse statusResp = client().execute(GetFeatureUpgradeStatusAction.INSTANCE, getStatusRequest).get();
+            logger.info(Strings.toString(statusResp));
+            assertThat(statusResp.getUpgradeStatus(), equalTo(GetFeatureUpgradeStatusResponse.UpgradeStatus.NO_MIGRATION_NEEDED));
+        });
+    }
+
     public void assertIndexHasCorrectProperties(
         Metadata metadata,
         String indexName,
@@ -343,6 +409,7 @@ public void createSystemIndexForDescriptor(SystemIndexDescriptor descriptor) thr
     static final String FEATURE_NAME = "A-test-feature"; // Sorts alphabetically before the feature from MultiFeatureMigrationIT
     static final String ORIGIN = FeatureMigrationIT.class.getSimpleName();
     static final String FlAG_SETTING_KEY = IndexMetadata.INDEX_PRIORITY_SETTING.getKey();
+    static final String INTERNAL_MANAGED_INDEX_NAME = ".int-man-old";
     static final int INDEX_DOC_COUNT = 100; // arbitrarily chosen
     public static final Version NEEDS_UPGRADE_VERSION = Version.V_6_0_0;
 
@@ -353,7 +420,7 @@ public void createSystemIndexForDescriptor(SystemIndexDescriptor descriptor) thr
     static final SystemIndexDescriptor INTERNAL_MANAGED = SystemIndexDescriptor.builder()
         .setIndexPattern(".int-man-*")
         .setAliasName(".internal-managed-alias")
-        .setPrimaryIndex(".int-man-old")
+        .setPrimaryIndex(INTERNAL_MANAGED_INDEX_NAME)
         .setType(SystemIndexDescriptor.Type.INTERNAL_MANAGED)
         .setSettings(createSimpleSettings(NEEDS_UPGRADE_VERSION, INTERNAL_MANAGED_FLAG_VALUE))
         .setMappings(createSimpleMapping(true, true, false)) // See note below

server/src/main/java/org/elasticsearch/action/admin/cluster/migration/TransportPostFeatureUpgradeAction.java

@@ -27,7 +27,9 @@
 import org.elasticsearch.upgrades.SystemIndexMigrationTaskParams;
 
 import java.util.Comparator;
+import java.util.EnumSet;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.action.admin.cluster.migration.TransportGetFeatureUpgradeStatusAction.getFeatureUpgradeStatus;
@@ -73,11 +75,15 @@ protected void masterOperation(
         ClusterState state,
         ActionListener<PostFeatureUpgradeResponse> listener
     ) throws Exception {
+        final Set<GetFeatureUpgradeStatusResponse.UpgradeStatus> upgradableStatuses = EnumSet.of(
+            GetFeatureUpgradeStatusResponse.UpgradeStatus.MIGRATION_NEEDED,
+            GetFeatureUpgradeStatusResponse.UpgradeStatus.ERROR
+        );
         List<PostFeatureUpgradeResponse.Feature> featuresToMigrate = systemIndices.getFeatures()
             .values()
             .stream()
             .map(feature -> getFeatureUpgradeStatus(state, feature))
-            .filter(status -> status.getUpgradeStatus().equals(GetFeatureUpgradeStatusResponse.UpgradeStatus.MIGRATION_NEEDED))
+            .filter(status -> upgradableStatuses.contains(status.getUpgradeStatus()))
             .map(GetFeatureUpgradeStatusResponse.FeatureUpgradeStatus::getFeatureName)
             .map(PostFeatureUpgradeResponse.Feature::new)
             .sorted(Comparator.comparing(PostFeatureUpgradeResponse.Feature::getFeatureName)) // consistent ordering to simplify testing