[Transform] Wait while index is blocked (#119542)

When the destination index is blocked, the bulk request is ignored.
Each subsequent trigger will check the cluster state if the index is
unblocked or else drop the trigger.

Users can call the ScheduleNow API to skip the index block check and let
the trigger start the next checkpoint - if the index is blocked then the
bulk request will fail again.

While the Transform is skipping triggers, the state will display as
`waiting` from the Get Stats API and on the Transform UI in Kibana.

docs/changelog/119542.yaml

@@ -0,0 +1,5 @@
+pr: 119542
+summary: Wait while index is blocked
+area: Transform
+type: enhancement
+issues: []

x-pack/plugin/transform/qa/multi-node-tests/src/javaRestTest/java/org/elasticsearch/xpack/transform/integration/TransformIT.java

@@ -28,6 +28,7 @@ import org.elasticsearch.xpack.core.transform.transforms.SyncConfig;
 import org.elasticsearch.xpack.core.transform.transforms.TimeRetentionPolicyConfig;
 import org.elasticsearch.xpack.core.transform.transforms.TimeSyncConfig;
 import org.elasticsearch.xpack.core.transform.transforms.TransformConfig;
+import org.elasticsearch.xpack.core.transform.transforms.TransformStats;
 import org.elasticsearch.xpack.core.transform.transforms.pivot.PivotConfig;
 import org.elasticsearch.xpack.core.transform.transforms.pivot.SingleGroupSource;
 import org.elasticsearch.xpack.core.transform.transforms.pivot.TermsGroupSource;
@@ -152,7 +153,7 @@ public class TransformIT extends TransformRestTestCase {
     public void testContinuousTransformCrud() throws Exception {
         var transformId = "transform-continuous-crud";
         var indexName = "continuous-crud-reviews";
-        createContinuousTransform(indexName, transformId);
+        createContinuousTransform(indexName, transformId, "reviews-by-user-business-day");
         var transformStats = getBasicTransformStats(transformId);
         assertThat(transformStats.get("state"), equalTo("started"));
 
@@ -181,7 +182,7 @@ public class TransformIT extends TransformRestTestCase {
         deleteTransform(transformId);
     }
 
-    private void createContinuousTransform(String indexName, String transformId) throws Exception {
+    private void createContinuousTransform(String indexName, String transformId, String destinationIndex) throws Exception {
         createReviewsIndex(indexName, 100, NUM_USERS, TransformIT::getUserIdForRow, TransformIT::getDateStringForRow);
 
         var groups = Map.of(
@@ -197,8 +198,9 @@ public class TransformIT extends TransformRestTestCase {
             .addAggregator(AggregationBuilders.avg("review_score").field("stars"))
             .addAggregator(AggregationBuilders.max("timestamp").field("timestamp"));
 
-        var config = createTransformConfigBuilder(transformId, "reviews-by-user-business-day", QueryConfig.matchAll(), indexName)
-            .setPivotConfig(createPivotConfig(groups, aggs))
+        var config = createTransformConfigBuilder(transformId, destinationIndex, QueryConfig.matchAll(), indexName).setPivotConfig(
+            createPivotConfig(groups, aggs)
+        )
             .setSyncConfig(new TimeSyncConfig("timestamp", TimeValue.timeValueSeconds(1)))
             .setSettings(new SettingsConfig.Builder().setAlignCheckpoints(false).build())
             .build();
@@ -216,7 +218,7 @@ public class TransformIT extends TransformRestTestCase {
     @SuppressWarnings("unchecked")
     public void testBasicContinuousTransformStats() throws Exception {
         var transformId = "transform-continuous-basic-stats";
-        createContinuousTransform("continuous-basic-stats-reviews", transformId);
+        createContinuousTransform("continuous-basic-stats-reviews", transformId, "reviews-by-user-business-day");
         var transformStats = getBasicTransformStats(transformId);
 
         assertEquals("started", XContentMapValues.extractValue("state", transformStats));
@@ -230,6 +232,40 @@ public class TransformIT extends TransformRestTestCase {
         deleteTransform(transformId);
     }
 
+    public void testDestinationIndexBlocked() throws Exception {
+        var transformId = "transform-continuous-blocked-destination";
+        var sourceIndexName = "source-reviews";
+        var destIndexName = "destination-reviews";
+
+        // create transform & indices, wait until 1st checkpoint is finished
+        createContinuousTransform(sourceIndexName, transformId, destIndexName);
+
+        // block destination index
+        Request request = new Request("PUT", destIndexName + "/_block/write");
+        assertAcknowledged(adminClient().performRequest(request));
+
+        // index more docs so the checkpoint tries to run, wait until transform stops
+        assertBusy(() -> {
+            indexDoc(42, sourceIndexName);
+            assertEquals(TransformStats.State.WAITING.value(), getTransformState(transformId));
+        }, 30, TimeUnit.SECONDS);
+
+        // unblock index
+        request = new Request("PUT", destIndexName + "/_settings");
+        request.setJsonEntity("""
+                { "blocks.write": false }
+            """);
+        assertAcknowledged(adminClient().performRequest(request));
+
+        assertBusy(() -> {
+            indexDoc(42, sourceIndexName);
+            assertEquals(TransformStats.State.STARTED.value(), getTransformState(transformId));
+        }, 30, TimeUnit.SECONDS);
+
+        stopTransform(transformId);
+        deleteTransform(transformId);
+    }
+
     public void testTransformLifecycleInALoop() throws Exception {
         String transformId = "lifecycle-in-a-loop";
         String indexName = transformId + "-src";
@@ -652,4 +688,17 @@ public class TransformIT extends TransformRestTestCase {
         bulkBuilder.append("\r\n");
         doBulk(bulkBuilder.toString(), true);
     }
+
+    private void indexDoc(long userId, String index) throws Exception {
+        StringBuilder bulkBuilder = new StringBuilder();
+        bulkBuilder.append(format("""
+            {"create":{"_index":"%s"}}
+            """, index));
+        String source = format("""
+            {"user_id":"user_%s","count":%s,"business_id":"business_%s","stars":%s,"timestamp":%s}
+            """, userId, 1, 2, 5, Instant.now().toEpochMilli());
+        bulkBuilder.append(source);
+        bulkBuilder.append("\r\n");
+        doBulk(bulkBuilder.toString(), true);
+    }
 }

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportGetTransformStatsAction.java

@@ -270,6 +270,9 @@ public class TransportGetTransformStatsAction extends TransportTasksAction<Trans
             && derivedState.equals(TransformStats.State.FAILED) == false) {
             derivedState = TransformStats.State.STOPPING;
             reason = Strings.isNullOrEmpty(reason) ? "transform is set to stop at the next checkpoint" : reason;
+        } else if (derivedState.equals(TransformStats.State.STARTED) && transformTask.getContext().isWaitingForIndexToUnblock()) {
+            derivedState = TransformStats.State.WAITING;
+            reason = Strings.isNullOrEmpty(reason) ? "transform is paused while destination index is blocked" : reason;
         }
         return new TransformStats(
             transformTask.getTransformId(),

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportScheduleNowTransformAction.java

@@ -128,6 +128,10 @@ public class TransportScheduleNowTransformAction extends TransportTasksAction<Tr
         TransformTask transformTask,
         ActionListener<Response> listener
     ) {
+        if (transformTask.getContext().isWaitingForIndexToUnblock()) {
+            logger.debug("[{}] Destination index is blocked. User requested a retry.", transformTask.getTransformId());
+            transformTask.getContext().setIsWaitingForIndexToUnblock(false);
+        }
         transformScheduler.scheduleNow(request.getId());
         listener.onResponse(Response.TRUE);
     }

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/ClientTransformIndexer.java

@@ -25,8 +25,10 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.action.search.TransportClosePointInTimeAction;
 import org.elasticsearch.action.search.TransportOpenPointInTimeAction;
 import org.elasticsearch.action.search.TransportSearchAction;
+import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.action.support.master.AcknowledgedRequest;
 import org.elasticsearch.client.internal.ParentTaskAssigningClient;
+import org.elasticsearch.cluster.block.ClusterBlockLevel;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -443,9 +445,36 @@ class ClientTransformIndexer extends TransformIndexer {
             logger.debug("[{}] schedule was triggered but the Transform is upgrading. Ignoring trigger.", getJobId());
             return false;
         }
+        if (context.isWaitingForIndexToUnblock()) {
+            if (destinationIndexHasWriteBlock()) {
+                logger.debug("[{}] schedule was triggered but the destination index has a write block. Ignoring trigger.", getJobId());
+                return false;
+            }
+            logger.debug("[{}] destination index is no longer blocked.", getJobId());
+            context.setIsWaitingForIndexToUnblock(false);
+        }
+
         return super.maybeTriggerAsyncJob(now);
     }
 
+    private boolean destinationIndexHasWriteBlock() {
+        var clusterState = clusterService.state();
+        if (clusterState == null) {
+            // if we can't determine if the index is blocked, we assume it isn't, even though the bulk request may fail again
+            return false;
+        }
+
+        var destinationIndexName = transformConfig.getDestination().getIndex();
+        var destinationIndex = indexNameExpressionResolver.concreteWriteIndex(
+            clusterState,
+            IndicesOptions.lenientExpandOpen(),
+            destinationIndexName,
+            true,
+            false
+        );
+        return destinationIndex != null && clusterState.blocks().indexBlocked(ClusterBlockLevel.WRITE, destinationIndex.getName());
+    }
+
     @Override
     protected void onStop() {
         closePointInTime();

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformContext.java

@@ -49,6 +49,14 @@ public class TransformContext {
     private volatile AuthorizationState authState;
     private volatile int pageSize = 0;
 
+    /**
+     * If the destination index is blocked (e.g. during a reindex), the Transform will fail to write to it.
+     * {@link TransformFailureHandler} will silence the error so the Transform automatically retries.
+     * Every time the Transform runs, it will check if the index is unblocked and reset this to false.
+     * Users can override this via the `_schedule_now` API.
+     */
+    private volatile boolean isWaitingForIndexToUnblock = false;
+
     // the checkpoint of this transform, storing the checkpoint until data indexing from source to dest is _complete_
     // Note: Each indexer run creates a new future checkpoint which becomes the current checkpoint only after the indexer run finished
     private final AtomicLong currentCheckpoint;
@@ -183,6 +191,14 @@ public class TransformContext {
         this.shouldRecreateDestinationIndex = shouldRecreateDestinationIndex;
     }
 
+    public boolean isWaitingForIndexToUnblock() {
+        return isWaitingForIndexToUnblock;
+    }
+
+    public void setIsWaitingForIndexToUnblock(boolean isWaitingForIndexToUnblock) {
+        this.isWaitingForIndexToUnblock = isWaitingForIndexToUnblock;
+    }
+
     public AuthorizationState getAuthState() {
         return authState;
     }

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/transforms/TransformFailureHandler.java

@@ -170,6 +170,7 @@ class TransformFailureHandler {
      */
     private void handleBulkIndexingException(BulkIndexingException bulkIndexingException, boolean unattended, int numFailureRetries) {
         if (bulkIndexingException.getCause() instanceof ClusterBlockException) {
+            context.setIsWaitingForIndexToUnblock(true);
             retryWithoutIncrementingFailureCount(
                 bulkIndexingException,
                 bulkIndexingException.getDetailedMessage(),

x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/action/TransportGetTransformStatsActionTests.java

@@ -343,6 +343,46 @@ public class TransportGetTransformStatsActionTests extends ESTestCase {
         );
     }
 
+    public void testDeriveStatsWithIndexBlock() {
+        String transformId = "transform-with-stats";
+        String reason = "transform is paused while destination index is blocked";
+        TransformIndexerStats stats = TransformIndexerStatsTests.randomStats();
+        TransformState runningState = new TransformState(
+            TransformTaskState.STARTED,
+            IndexerState.STARTED,
+            null,
+            0,
+            null,
+            null,
+            null,
+            false,
+            null
+        );
+
+        var context = new TransformContext(TransformTaskState.STARTED, "", 0, mock());
+        context.setIsWaitingForIndexToUnblock(true);
+        var task = mock(TransformTask.class);
+        when(task.getContext()).thenReturn(context);
+        when(task.getTransformId()).thenReturn(transformId);
+        when(task.getState()).thenReturn(runningState);
+        when(task.getStats()).thenReturn(stats);
+
+        assertThat(
+            TransportGetTransformStatsAction.deriveStats(task, null),
+            equalTo(
+                new TransformStats(
+                    transformId,
+                    TransformStats.State.WAITING,
+                    reason,
+                    null,
+                    stats,
+                    TransformCheckpointingInfo.EMPTY,
+                    TransformHealth.GREEN
+                )
+            )
+        );
+    }
+
     private void withIdStateAndStats(String transformId, TransformState state, TransformIndexerStats stats) {
         when(task.getTransformId()).thenReturn(transformId);
         when(task.getState()).thenReturn(state);

x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/ClientTransformIndexerTests.java

@@ -22,13 +22,18 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.action.search.ShardSearchFailure;
 import org.elasticsearch.action.support.ActionTestUtils;
 import org.elasticsearch.client.internal.ParentTaskAssigningClient;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.block.ClusterBlockLevel;
+import org.elasticsearch.cluster.block.ClusterBlocks;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
+import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.CompositeBytesReference;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.core.Tuple;
+import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexNotFoundException;
 import org.elasticsearch.search.SearchContextMissingException;
 import org.elasticsearch.search.SearchHit;
@@ -44,6 +49,7 @@ import org.elasticsearch.test.client.NoOpClient;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.ActionNotFoundTransportException;
 import org.elasticsearch.xpack.core.indexing.IndexerState;
+import org.elasticsearch.xpack.core.transform.TransformMetadata;
 import org.elasticsearch.xpack.core.transform.transforms.SettingsConfig;
 import org.elasticsearch.xpack.core.transform.transforms.SourceConfig;
 import org.elasticsearch.xpack.core.transform.transforms.TransformCheckpoint;
@@ -53,6 +59,7 @@ import org.elasticsearch.xpack.core.transform.transforms.TransformEffectiveSetti
 import org.elasticsearch.xpack.core.transform.transforms.TransformIndexerPosition;
 import org.elasticsearch.xpack.core.transform.transforms.TransformIndexerStats;
 import org.elasticsearch.xpack.core.transform.transforms.TransformProgress;
+import org.elasticsearch.xpack.core.transform.transforms.TransformTaskState;
 import org.elasticsearch.xpack.core.transform.transforms.persistence.TransformInternalIndexConstants;
 import org.elasticsearch.xpack.transform.TransformExtension;
 import org.elasticsearch.xpack.transform.TransformNode;
@@ -77,6 +84,10 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.stream.IntStream;
 
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -467,6 +478,53 @@ public class ClientTransformIndexerTests extends ESTestCase {
         }
     }
 
+    public void testIndexBlocked() {
+        var service = serviceWithBlockCheck(true);
+        var context = new TransformContext(TransformTaskState.STARTED, "", 0, mock());
+
+        var indexer = createTestIndexer(mock(), service, resolver(), context);
+        context.setIsWaitingForIndexToUnblock(true);
+
+        assertFalse(indexer.maybeTriggerAsyncJob(Instant.now().toEpochMilli()));
+        assertTrue(context.isWaitingForIndexToUnblock());
+    }
+
+    public void testIndexUnblocked() {
+        var service = serviceWithBlockCheck(false);
+        // set state to failed so that TransformIndexer returns false
+        var context = new TransformContext(TransformTaskState.FAILED, "", 0, mock());
+
+        var indexer = createTestIndexer(mock(), service, resolver(), context);
+        context.setIsWaitingForIndexToUnblock(true);
+
+        assertFalse(indexer.maybeTriggerAsyncJob(Instant.now().toEpochMilli()));
+        // ClientTransformIndexer's maybeTriggerAsyncJob should reset isWaitingForIndexToUnblock to false
+        assertFalse(context.isWaitingForIndexToUnblock());
+    }
+
+    private ClusterService serviceWithBlockCheck(boolean checkResponse) {
+        var clusterBlocks = mock(ClusterBlocks.class);
+        when(clusterBlocks.indexBlocked(eq(ClusterBlockLevel.WRITE), anyString())).thenReturn(checkResponse);
+        var metadata = mock(Metadata.class);
+        when(metadata.custom(eq(TransformMetadata.TYPE))).thenReturn(TransformMetadata.EMPTY_METADATA);
+        var clusterState = mock(ClusterState.class);
+        when(clusterState.blocks()).thenReturn(clusterBlocks);
+        when(clusterState.getMetadata()).thenReturn(metadata);
+        var clusterService = mock(ClusterService.class);
+        when(clusterService.state()).thenReturn(clusterState);
+        return clusterService;
+    }
+
+    private IndexNameExpressionResolver resolver() {
+        var resolver = mock(IndexNameExpressionResolver.class);
+        when(resolver.concreteWriteIndex(any(), any(), any(), anyBoolean(), anyBoolean())).thenAnswer(ans -> {
+            Index destIndex = mock();
+            when(destIndex.getName()).thenReturn(ans.getArgument(2));
+            return destIndex;
+        });
+        return resolver;
+    }
+
     private static class MockClientTransformIndexer extends ClientTransformIndexer {
 
         MockClientTransformIndexer(
@@ -627,13 +685,22 @@ public class ClientTransformIndexerTests extends ESTestCase {
     }
 
     private ClientTransformIndexer createTestIndexer(ParentTaskAssigningClient client) {
+        return createTestIndexer(client, mock(), mock(), mock(TransformContext.class));
+    }
+
+    private ClientTransformIndexer createTestIndexer(
+        ParentTaskAssigningClient client,
+        ClusterService service,
+        IndexNameExpressionResolver resolver,
+        TransformContext context
+    ) {
         ThreadPool threadPool = mock(ThreadPool.class);
         when(threadPool.executor("generic")).thenReturn(mock(ExecutorService.class));
 
         return new ClientTransformIndexer(
             mock(ThreadPool.class),
-            mock(ClusterService.class),
-            mock(IndexNameExpressionResolver.class),
+            service,
+            resolver,
             mock(TransformExtension.class),
             new TransformServices(
                 mock(IndexBasedTransformConfigManager.class),
@@ -652,7 +719,7 @@ public class ClientTransformIndexerTests extends ESTestCase {
             new TransformCheckpoint("transform", Instant.now().toEpochMilli(), 0L, Collections.emptyMap(), Instant.now().toEpochMilli()),
             new TransformCheckpoint("transform", Instant.now().toEpochMilli(), 2L, Collections.emptyMap(), Instant.now().toEpochMilli()),
             new SeqNoPrimaryTermAndIndex(1, 1, TransformInternalIndexConstants.LATEST_INDEX_NAME),
-            mock(TransformContext.class),
+            context,
             false
         );
     }

x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/TransformFailureHandlerTests.java

@@ -93,7 +93,7 @@ public class TransformFailureHandlerTests extends ESTestCase {
             randomBoolean()
         );
 
-        List.of(true, false).forEach((unattended) -> { assertRetryFailureCountNotIncremented(bulkIndexingException, unattended); });
+        List.of(true, false).forEach((unattended) -> { assertClusterBlockHandled(bulkIndexingException, unattended); });
     }
 
     public void testHandleIndexerFailure_IrrecoverableBulkIndexException() {
@@ -197,7 +197,7 @@ public class TransformFailureHandlerTests extends ESTestCase {
         }
     }
 
-    private void assertRetryFailureCountNotIncremented(Exception e, boolean unattended) {
+    private void assertClusterBlockHandled(Exception e, boolean unattended) {
         String transformId = randomAlphaOfLength(10);
         SettingsConfig settings = new SettingsConfig.Builder().setNumFailureRetries(2).setUnattended(unattended).build();
 
@@ -211,6 +211,7 @@ public class TransformFailureHandlerTests extends ESTestCase {
         assertNoFailure(handler, e, contextListener, settings, false);
         assertNoFailure(handler, e, contextListener, settings, false);
         assertNoFailure(handler, e, contextListener, settings, false);
+        assertTrue(context.isWaitingForIndexToUnblock());
     }
 
     private void assertFailure(Exception e) {