Skip the validation when retrieving the index mode during reindexing a time series data stream. (#127824)

During reindexing we retrieve the index mode from the template settings. However, we do not fully resolve the settings as we do when validating a template or when creating a data stream. This results on throwing the error reported in #125607.

I do not see a reason to not fix this as suggested in #125607 (comment).

Fixes: #125607
(cherry picked from commit 077b6b9)

# Conflicts:
#	modules/data-streams/build.gradle
#	modules/reindex/src/main/java/org/elasticsearch/reindex/Reindexer.java

Author: gmarouli

docs/changelog/127824.yaml

@@ -0,0 +1,6 @@
+pr: 127824
+summary: Skip the validation when retrieving the index mode during reindexing a time
+  series data stream
+area: TSDB
+type: bug
+issues: []

modules/data-streams/build.gradle

@@ -14,14 +14,15 @@ esplugin {
 restResources {
   restApi {
     include 'bulk', 'count', 'search', '_common', 'indices', 'index', 'cluster', 'rank_eval', 'reindex', 'update_by_query', 'delete_by_query',
-      'eql', 'data_stream', 'ingest', 'cat', 'capabilities'
+      'eql', 'data_stream', 'ingest', 'cat', 'capabilities', 'reindex'
   }
 }
 
 dependencies {
   testImplementation project(path: ':test:test-clusters')
   testImplementation project(":modules:mapper-extras")
   internalClusterTestImplementation project(":modules:mapper-extras")
+  internalClusterTestImplementation project(':modules:reindex')
 }
 
 tasks.withType(StandaloneRestIntegTestTask).configureEach {

modules/data-streams/src/internalClusterTest/java/org/elasticsearch/datastreams/TSDBIndexingIT.java

@@ -13,31 +13,40 @@
 import org.elasticsearch.action.admin.indices.diskusage.TransportAnalyzeIndexDiskUsageAction;
 import org.elasticsearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.elasticsearch.action.admin.indices.get.GetIndexRequest;
+import org.elasticsearch.action.admin.indices.get.GetIndexResponse;
 import org.elasticsearch.action.admin.indices.refresh.RefreshRequest;
 import org.elasticsearch.action.admin.indices.rollover.RolloverRequest;
 import org.elasticsearch.action.admin.indices.segments.IndicesSegmentsRequest;
 import org.elasticsearch.action.admin.indices.stats.IndicesStatsRequest;
 import org.elasticsearch.action.admin.indices.template.put.PutComponentTemplateAction;
 import org.elasticsearch.action.admin.indices.template.put.TransportPutComposableIndexTemplateAction;
 import org.elasticsearch.action.bulk.BulkRequest;
+import org.elasticsearch.action.bulk.BulkRequestBuilder;
+import org.elasticsearch.action.bulk.BulkResponse;
 import org.elasticsearch.action.bulk.IndexDocFailureStoreStatus;
 import org.elasticsearch.action.get.GetRequest;
 import org.elasticsearch.action.index.IndexRequest;
 import org.elasticsearch.action.search.SearchRequest;
 import org.elasticsearch.action.support.WriteRequest;
 import org.elasticsearch.cluster.metadata.ComponentTemplate;
 import org.elasticsearch.cluster.metadata.ComposableIndexTemplate;
+import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Template;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.time.DateFormatter;
 import org.elasticsearch.common.time.FormatNames;
 import org.elasticsearch.common.xcontent.XContentHelper;
+import org.elasticsearch.index.IndexMode;
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.query.RangeQueryBuilder;
+import org.elasticsearch.index.reindex.BulkByScrollResponse;
+import org.elasticsearch.index.reindex.ReindexAction;
+import org.elasticsearch.index.reindex.ReindexRequest;
 import org.elasticsearch.indices.InvalidIndexTemplateException;
 import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.reindex.ReindexPlugin;
 import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.test.ESSingleNodeTestCase;
@@ -53,6 +62,7 @@
 
 import static org.elasticsearch.test.MapMatcher.assertMap;
 import static org.elasticsearch.test.MapMatcher.matchesMap;
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertResponse;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
@@ -98,7 +108,7 @@ public class TSDBIndexingIT extends ESSingleNodeTestCase {
 
     @Override
     protected Collection<Class<? extends Plugin>> getPlugins() {
-        return List.of(DataStreamsPlugin.class, InternalSettingsPlugin.class);
+        return List.of(DataStreamsPlugin.class, InternalSettingsPlugin.class, ReindexPlugin.class);
     }
 
     @Override
@@ -557,6 +567,60 @@ public void testTrimId() throws Exception {
         });
     }
 
+    public void testReindexing() throws Exception {
+        String dataStreamName = "my-ds";
+        String reindexedDataStreamName = "my-reindexed-ds";
+        var putTemplateRequest = new TransportPutComposableIndexTemplateAction.Request("id");
+        putTemplateRequest.indexTemplate(
+            ComposableIndexTemplate.builder()
+                .indexPatterns(List.of(dataStreamName, reindexedDataStreamName))
+                .template(
+                    new Template(
+                        Settings.builder().put("index.mode", "time_series").build(),
+                        new CompressedXContent(MAPPING_TEMPLATE),
+                        null
+                    )
+                )
+                .dataStreamTemplate(new ComposableIndexTemplate.DataStreamTemplate(false, false))
+                .build()
+        );
+        assertAcked(client().execute(TransportPutComposableIndexTemplateAction.TYPE, putTemplateRequest));
+
+        // index doc
+        long docCount = randomLongBetween(10, 50);
+        Instant startTime = Instant.now();
+        BulkRequestBuilder bulkRequestBuilder = client().prepareBulk();
+        bulkRequestBuilder.setRefreshPolicy(WriteRequest.RefreshPolicy.IMMEDIATE);
+        for (int i = 0; i < docCount; i++) {
+            IndexRequest indexRequest = new IndexRequest(dataStreamName).opType(DocWriteRequest.OpType.CREATE);
+            indexRequest.source(DOC.replace("$time", formatInstant(startTime.plusSeconds(i))), XContentType.JSON);
+            bulkRequestBuilder.add(indexRequest);
+        }
+        BulkResponse bulkResponse = bulkRequestBuilder.get();
+        assertThat(bulkResponse.hasFailures(), is(false));
+
+        BulkByScrollResponse reindexResponse = safeGet(
+            client().execute(
+                ReindexAction.INSTANCE,
+                new ReindexRequest().setSourceIndices(dataStreamName).setDestIndex(reindexedDataStreamName).setDestOpType("create")
+            )
+        );
+        assertThat(reindexResponse.getCreated(), equalTo(docCount));
+
+        GetIndexResponse getIndexResponse = safeGet(
+            indicesAdmin().getIndex(new GetIndexRequest(TEST_REQUEST_TIMEOUT).indices(dataStreamName, reindexedDataStreamName))
+        );
+        assertThat(getIndexResponse.getIndices().length, equalTo(2));
+        var index1 = getIndexResponse.getIndices()[0];
+        var index2 = getIndexResponse.getIndices()[1];
+        assertThat(getIndexResponse.getSetting(index1, IndexSettings.MODE.getKey()), equalTo(IndexMode.TIME_SERIES.getName()));
+        assertThat(getIndexResponse.getSetting(index2, IndexSettings.MODE.getKey()), equalTo(IndexMode.TIME_SERIES.getName()));
+        assertThat(
+            getIndexResponse.getSetting(index2, IndexMetadata.INDEX_ROUTING_PATH.getKey()),
+            equalTo(getIndexResponse.getSetting(index1, IndexMetadata.INDEX_ROUTING_PATH.getKey()))
+        );
+    }
+
     static String formatInstant(Instant instant) {
         return DateFormatter.forPattern(FormatNames.STRICT_DATE_OPTIONAL_TIME.getName()).format(instant);
     }

modules/reindex/src/main/java/org/elasticsearch/reindex/Reindexer.java

@@ -254,7 +254,9 @@ private IndexMode destinationIndexMode(ClusterState state) {
                 return IndexMode.STANDARD;
             }
             Settings settings = MetadataIndexTemplateService.resolveSettings(state.metadata(), template);
-            return IndexSettings.MODE.get(settings);
+            // We retrieve the setting without performing any validation because that the template has already been validated
+            String indexMode = settings.get(IndexSettings.MODE.getKey());
+            return indexMode == null ? IndexMode.STANDARD : IndexMode.fromString(indexMode);
         }
 
         @Override