[8.19] Add index mode to get data stream API (#122486) (#128154)

* Add index mode to get data stream API (#122486)

This commit adds the `index_mode` for both the data stream and each
backing index to the output of `GET /_data_stream`. An example looks
like:

```
{
  "data_streams" : [
    {
      "name" : "foo-things",
      "indices" : [
        {
          "index_name" : ".ds-foo-things-2025.02.13-000001",
          ...
          "index_mode" : "standard"
        }
      ],
      ...
      "index_mode" : "standard"
    },
    {
      "name" : "logs-foo-bar",
      "indices" : [
        {
          "index_name" : ".ds-logs-foo-bar-2025.02.13-000001",
          ...
          "index_mode" : "logsdb"
        },
        {
          "index_name" : ".ds-logs-foo-bar-2025.02.13-000002",
          ...
          "index_mode" : "logsdb"
        }
      ],
      ...
      "index_mode" : "logsdb",
    }
  ]
}
```

(cherry picked from commit 47706b505f6510c3314a8a83c8c3f68c3d0eaefc)

# Conflicts:
#	docs/reference/indices/get-data-stream.asciidoc
#	server/src/main/java/org/elasticsearch/TransportVersions.java
#	server/src/main/java/org/elasticsearch/action/datastreams/GetDataStreamAction.java
#	server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java
#	x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/LogsdbIndexModeSettingsProvider.java
#	x-pack/plugin/logsdb/src/test/java/org/elasticsearch/xpack/logsdb/LogsdbIndexModeSettingsProviderTests.java

* Fix compilation for backport

* Fix docs

docs/changelog/122486.yaml

@@ -0,0 +1,5 @@
+pr: 122486
+summary: Add index mode to get data stream API
+area: Data streams
+type: enhancement
+issues: []

docs/reference/data-streams/change-mappings-and-settings.asciidoc

@@ -575,13 +575,15 @@ stream's oldest backing index.
           "index_name": ".ds-my-data-stream-2099.03.07-000001", <1>
           "index_uuid": "Gpdiyq8sRuK9WuthvAdFbw",
           "prefer_ilm": true,
-          "managed_by": "Unmanaged"
+          "managed_by": "Unmanaged",
+          "index_mode" : "standard"
         },
         {
           "index_name": ".ds-my-data-stream-2099.03.08-000002",
           "index_uuid": "_eEfRrFHS9OyhqWntkgHAQ",
           "prefer_ilm": true,
-          "managed_by": "Unmanaged"
+          "managed_by": "Unmanaged",
+          "index_mode" : "standard"
         }
       ],
       "generation": 2,
@@ -593,6 +595,7 @@ stream's oldest backing index.
       "system": false,
       "allow_custom_routing": false,
       "replicated": false,
+      "index_mode": "standard",
       "rollover_on_write": false
     }
   ]

docs/reference/data-streams/downsampling-manual.asciidoc

@@ -360,6 +360,7 @@ This returns:
           "index_name": ".ds-my-data-stream-2023.07.26-000001", <1>
           "index_uuid": "ltOJGmqgTVm4T-Buoe7Acg",
           "prefer_ilm": true,
+          "index_mode": "time_series",
           "managed_by": "Unmanaged"
         }
       ],
@@ -373,6 +374,7 @@ This returns:
       "allow_custom_routing": false,
       "replicated": false,
       "rollover_on_write": false,
+      "index_mode": "time_series",
       "time_series": {
         "temporal_ranges": [
           {

docs/reference/data-streams/lifecycle/tutorial-migrate-data-stream-from-ilm-to-dsl.asciidoc

@@ -118,14 +118,16 @@ and that the next generation index will also be managed by {ilm-init}:
           "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
           "prefer_ilm": true,                                       <2>
           "ilm_policy": "pre-dsl-ilm-policy",                       <3>
-          "managed_by": "Index Lifecycle Management"                <4>
+          "managed_by": "Index Lifecycle Management",               <4>
+          "index_mode": "standard"
         },
         {
           "index_name": ".ds-dsl-data-stream-2023.10.19-000002",
           "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
-          "managed_by": "Index Lifecycle Management"
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
         }
       ],
       "generation": 2,
@@ -138,6 +140,7 @@ and that the next generation index will also be managed by {ilm-init}:
       "system": false,
       "allow_custom_routing": false,
       "replicated": false,
+      "index_mode": "standard",
       "rollover_on_write": false
     }
   ]
@@ -251,14 +254,16 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
-          "managed_by": "Index Lifecycle Management"                <1>
+          "managed_by": "Index Lifecycle Management",               <1>
+          "index_mode": "standard"
         },
         {
           "index_name": ".ds-dsl-data-stream-2023.10.19-000002",
           "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
-          "managed_by": "Index Lifecycle Management"                <2>
+          "managed_by": "Index Lifecycle Management",               <2>
+          "index_mode": "standard"
         }
       ],
       "generation": 2,
@@ -277,6 +282,7 @@ GET _data_stream/dsl-data-stream
       "system": false,
       "allow_custom_routing": false,
       "replicated": false,
+      "index_mode": "standard",
       "rollover_on_write": false
     }
   ]
@@ -324,6 +330,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Index Lifecycle Management"                <1>
         },
         {
@@ -331,6 +338,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Index Lifecycle Management"                <2>
         },
         {
@@ -338,6 +346,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "PA_JquKGSiKcAKBA8abcd1",
           "prefer_ilm": false,                                      <3>
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Data stream lifecycle"                     <4>
         }
       ],
@@ -357,6 +366,7 @@ GET _data_stream/dsl-data-stream
       "system": false,
       "allow_custom_routing": false,
       "replicated": false,
+      "index_mode": "standard",
       "rollover_on_write": false
     }
   ]
@@ -424,6 +434,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Index Lifecycle Management"
         },
         {
@@ -431,6 +442,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
           "prefer_ilm": true,
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Index Lifecycle Management"
         },
         {
@@ -438,6 +450,7 @@ GET _data_stream/dsl-data-stream
           "index_uuid": "PA_JquKGSiKcAKBA8abcd1",
           "prefer_ilm": false,
           "ilm_policy": "pre-dsl-ilm-policy",
+          "index_mode": "standard",
           "managed_by": "Index Lifecycle Management"                <1>
         }
       ],
@@ -455,6 +468,7 @@ GET _data_stream/dsl-data-stream
       "system": false,
       "allow_custom_routing": false,
       "replicated": false,
+      "index_mode": "standard",
       "rollover_on_write": false
     }
   ]

docs/reference/indices/get-data-stream.asciidoc

@@ -304,14 +304,16 @@ The API returns the following response:
           "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
           "prefer_ilm": true,
           "ilm_policy": "my-lifecycle-policy",
-          "managed_by": "Index Lifecycle Management"
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
         },
         {
           "index_name": ".ds-my-data-stream-2099.03.08-000002",
           "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
           "prefer_ilm": true,
           "ilm_policy": "my-lifecycle-policy",
-          "managed_by": "Index Lifecycle Management"
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
         }
       ],
       "generation": 2,
@@ -319,6 +321,7 @@ The API returns the following response:
         "my-meta-field": "foo"
       },
       "status": "GREEN",
+      "index_mode": "standard",
       "next_generation_managed_by": "Index Lifecycle Management",
       "prefer_ilm": true,
       "template": "my-index-template",
@@ -340,7 +343,8 @@ The API returns the following response:
           "index_uuid": "3liBu2SYS5axasRt6fUIpA",
           "prefer_ilm": true,
           "ilm_policy": "my-lifecycle-policy",
-          "managed_by": "Index Lifecycle Management"
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
         }
       ],
       "generation": 1,
@@ -348,6 +352,7 @@ The API returns the following response:
         "my-meta-field": "foo"
       },
       "status": "YELLOW",
+      "index_mode": "standard",
       "next_generation_managed_by": "Index Lifecycle Management",
       "prefer_ilm": true,
       "template": "my-index-template",

modules/data-streams/src/main/java/org/elasticsearch/datastreams/action/TransportGetDataStreamsAction.java

@@ -24,6 +24,7 @@ import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.block.ClusterBlockException;
 import org.elasticsearch.cluster.block.ClusterBlockLevel;
 import org.elasticsearch.cluster.health.ClusterStateHealth;
+import org.elasticsearch.cluster.metadata.ComposableIndexTemplate;
 import org.elasticsearch.cluster.metadata.DataStream;
 import org.elasticsearch.cluster.metadata.DataStreamFailureStoreSettings;
 import org.elasticsearch.cluster.metadata.DataStreamGlobalRetentionSettings;
@@ -39,6 +40,9 @@ import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.Tuple;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexMode;
+import org.elasticsearch.index.IndexSettingProvider;
+import org.elasticsearch.index.IndexSettingProviders;
+import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.indices.SystemDataStreamDescriptor;
 import org.elasticsearch.indices.SystemIndices;
 import org.elasticsearch.injection.guice.Inject;
@@ -52,6 +56,7 @@ import java.util.Arrays;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.stream.Collectors;
 
@@ -67,6 +72,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
     private final ClusterSettings clusterSettings;
     private final DataStreamGlobalRetentionSettings globalRetentionSettings;
     private final DataStreamFailureStoreSettings dataStreamFailureStoreSettings;
+    private final IndexSettingProviders indexSettingProviders;
     private final Client client;
 
     @Inject
@@ -79,6 +85,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
         SystemIndices systemIndices,
         DataStreamGlobalRetentionSettings globalRetentionSettings,
         DataStreamFailureStoreSettings dataStreamFailureStoreSettings,
+        IndexSettingProviders indexSettingProviders,
         Client client
     ) {
         super(
@@ -96,6 +103,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
         this.globalRetentionSettings = globalRetentionSettings;
         clusterSettings = clusterService.getClusterSettings();
         this.dataStreamFailureStoreSettings = dataStreamFailureStoreSettings;
+        this.indexSettingProviders = indexSettingProviders;
         this.client = new OriginSettingClient(client, "stack");
     }
 
@@ -128,6 +136,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
                             clusterSettings,
                             globalRetentionSettings,
                             dataStreamFailureStoreSettings,
+                            indexSettingProviders,
                             maxTimestamps
                         )
                     );
@@ -148,12 +157,43 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
                     clusterSettings,
                     globalRetentionSettings,
                     dataStreamFailureStoreSettings,
+                    indexSettingProviders,
                     null
                 )
             );
         }
     }
 
+    /**
+     * Resolves the index mode ("index.mode" setting) for the given data stream, from the template or additional setting providers
+     */
+    @Nullable
+    static IndexMode resolveMode(
+        ClusterState state,
+        IndexSettingProviders indexSettingProviders,
+        DataStream dataStream,
+        Settings settings,
+        ComposableIndexTemplate indexTemplate
+    ) {
+        IndexMode indexMode = state.metadata().retrieveIndexModeFromTemplate(indexTemplate);
+        for (IndexSettingProvider provider : indexSettingProviders.getIndexSettingProviders()) {
+            Settings addlSettinsg = provider.getAdditionalIndexSettings(
+                MetadataIndexTemplateService.VALIDATE_INDEX_NAME,
+                dataStream.getName(),
+                indexMode,
+                state.metadata(),
+                Instant.now(),
+                settings,
+                List.of()
+            );
+            var rawMode = addlSettinsg.get(IndexSettings.MODE.getKey());
+            if (rawMode != null) {
+                indexMode = Enum.valueOf(IndexMode.class, rawMode.toUpperCase(Locale.ROOT));
+            }
+        }
+        return indexMode;
+    }
+
     static GetDataStreamAction.Response innerOperation(
         ClusterState state,
         GetDataStreamAction.Request request,
@@ -162,6 +202,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
         ClusterSettings clusterSettings,
         DataStreamGlobalRetentionSettings globalRetentionSettings,
         DataStreamFailureStoreSettings dataStreamFailureStoreSettings,
+        IndexSettingProviders indexSettingProviders,
         @Nullable Map<String, Long> maxTimestamps
     ) {
         List<DataStream> dataStreams = getDataStreams(state, indexNameExpressionResolver, request);
@@ -173,6 +214,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
             final String indexTemplate;
             boolean indexTemplatePreferIlmValue = true;
             String ilmPolicyName = null;
+            IndexMode indexMode = dataStream.getIndexMode();
             if (dataStream.isSystem()) {
                 SystemDataStreamDescriptor dataStreamDescriptor = systemIndices.findMatchingDataStreamDescriptor(dataStream.getName());
                 indexTemplate = dataStreamDescriptor != null ? dataStreamDescriptor.getDataStreamName() : null;
@@ -182,6 +224,15 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
                         dataStreamDescriptor.getComponentTemplates()
                     );
                     ilmPolicyName = settings.get(IndexMetadata.LIFECYCLE_NAME);
+                    if (indexMode == null) {
+                        indexMode = resolveMode(
+                            state,
+                            indexSettingProviders,
+                            dataStream,
+                            settings,
+                            dataStreamDescriptor.getComposableIndexTemplate()
+                        );
+                    }
                     indexTemplatePreferIlmValue = PREFER_ILM_SETTING.get(settings);
                 }
             } else {
@@ -189,6 +240,15 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
                 if (indexTemplate != null) {
                     Settings settings = MetadataIndexTemplateService.resolveSettings(state.metadata(), indexTemplate);
                     ilmPolicyName = settings.get(IndexMetadata.LIFECYCLE_NAME);
+                    if (indexMode == null && state.metadata().templatesV2().get(indexTemplate) != null) {
+                        indexMode = resolveMode(
+                            state,
+                            indexSettingProviders,
+                            dataStream,
+                            settings,
+                            state.metadata().templatesV2().get(indexTemplate)
+                        );
+                    }
                     indexTemplatePreferIlmValue = PREFER_ILM_SETTING.get(settings);
                 } else {
                     LOGGER.warn(
@@ -280,7 +340,9 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
                     timeSeries,
                     backingIndicesSettingsValues,
                     indexTemplatePreferIlmValue,
-                    maxTimestamps == null ? null : maxTimestamps.get(dataStream.getName())
+                    maxTimestamps == null ? null : maxTimestamps.get(dataStream.getName()),
+                    // Default to standard mode if not specified; should we set this to "unset" or "unspecified" instead?
+                    indexMode == null ? IndexMode.STANDARD.getName() : indexMode.getName()
                 )
             );
         }
@@ -310,7 +372,11 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadAction
             } else {
                 managedBy = ManagedBy.UNMANAGED;
             }
-            backingIndicesSettingsValues.put(index, new IndexProperties(preferIlm, indexMetadata.getLifecyclePolicyName(), managedBy));
+            String indexMode = IndexSettings.MODE.get(indexMetadata.getSettings()).getName();
+            backingIndicesSettingsValues.put(
+                index,
+                new IndexProperties(preferIlm, indexMetadata.getLifecyclePolicyName(), managedBy, indexMode)
+            );
         }
     }
 

modules/data-streams/src/test/java/org/elasticsearch/datastreams/action/GetDataStreamsResponseTests.java

@@ -92,13 +92,13 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             String ilmPolicyName = "rollover-30days";
             Map<Index, Response.IndexProperties> indexSettingsValues = Map.of(
                 firstGenerationIndex,
-                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM),
+                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM, null),
                 secondGenerationIndex,
-                new Response.IndexProperties(false, ilmPolicyName, ManagedBy.LIFECYCLE),
+                new Response.IndexProperties(false, ilmPolicyName, ManagedBy.LIFECYCLE, null),
                 writeIndex,
-                new Response.IndexProperties(false, null, ManagedBy.LIFECYCLE),
+                new Response.IndexProperties(false, null, ManagedBy.LIFECYCLE, null),
                 failureStoreIndex,
-                new Response.IndexProperties(false, null, ManagedBy.LIFECYCLE)
+                new Response.IndexProperties(false, null, ManagedBy.LIFECYCLE, null)
             );
 
             Response.DataStreamInfo dataStreamInfo = new Response.DataStreamInfo(
@@ -110,6 +110,7 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 null,
                 indexSettingsValues,
                 false,
+                null,
                 null
             );
             Response response = new Response(List.of(dataStreamInfo));
@@ -191,13 +192,13 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             String ilmPolicyName = "rollover-30days";
             Map<Index, Response.IndexProperties> indexSettingsValues = Map.of(
                 firstGenerationIndex,
-                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM),
+                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM, null),
                 secondGenerationIndex,
-                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM),
+                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM, null),
                 writeIndex,
-                new Response.IndexProperties(false, null, ManagedBy.UNMANAGED),
+                new Response.IndexProperties(false, null, ManagedBy.UNMANAGED, null),
                 failureStoreIndex,
-                new Response.IndexProperties(false, null, ManagedBy.UNMANAGED)
+                new Response.IndexProperties(false, null, ManagedBy.UNMANAGED, null)
             );
 
             Response.DataStreamInfo dataStreamInfo = new Response.DataStreamInfo(
@@ -209,6 +210,7 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 null,
                 indexSettingsValues,
                 false,
+                null,
                 null
             );
             Response response = new Response(List.of(dataStreamInfo));
@@ -279,13 +281,13 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             String ilmPolicyName = "rollover-30days";
             Map<Index, Response.IndexProperties> indexSettingsValues = Map.of(
                 firstGenerationIndex,
-                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM),
+                new Response.IndexProperties(true, ilmPolicyName, ManagedBy.ILM, null),
                 secondGenerationIndex,
-                new Response.IndexProperties(false, ilmPolicyName, ManagedBy.LIFECYCLE),
+                new Response.IndexProperties(false, ilmPolicyName, ManagedBy.LIFECYCLE, null),
                 writeIndex,
-                new Response.IndexProperties(true, null, ManagedBy.LIFECYCLE),
+                new Response.IndexProperties(true, null, ManagedBy.LIFECYCLE, null),
                 failureStoreIndex,
-                new Response.IndexProperties(randomBoolean(), ilmPolicyName, ManagedBy.LIFECYCLE)
+                new Response.IndexProperties(randomBoolean(), ilmPolicyName, ManagedBy.LIFECYCLE, null)
             );
 
             Response.DataStreamInfo dataStreamInfo = new Response.DataStreamInfo(
@@ -297,6 +299,7 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 null,
                 indexSettingsValues,
                 false,
+                null,
                 null
             );
             Response response = new Response(List.of(dataStreamInfo));
@@ -359,7 +362,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                         new Response.IndexProperties(
                             randomBoolean(),
                             randomAlphaOfLengthBetween(50, 100),
-                            randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE
+                            randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE,
+                            null
                         )
                     )
             );
@@ -378,7 +382,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             timeSeries,
             indexSettings,
             templatePreferIlm,
-            maximumTimestamp
+            maximumTimestamp,
+            null
         );
     }
 
@@ -399,7 +404,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 new Response.IndexProperties(
                     randomBoolean(),
                     randomAlphaOfLengthBetween(50, 100),
-                    randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE
+                    randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE,
+                    randomBoolean() ? randomFrom(IndexMode.values()).getName() : null
                 )
             );
         }
@@ -417,7 +423,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             timeSeries != null ? new Response.TimeSeries(timeSeries) : null,
             generateRandomIndexSettingsValues(),
             randomBoolean(),
-            usually() ? randomNonNegativeLong() : null
+            usually() ? randomNonNegativeLong() : null,
+            usually() ? randomFrom(IndexMode.values()).getName() : null
         );
     }
 }

modules/data-streams/src/test/java/org/elasticsearch/datastreams/action/TransportGetDataStreamsActionTests.java

@@ -23,7 +23,9 @@ 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.IndexMode;
 import org.elasticsearch.index.IndexNotFoundException;
+import org.elasticsearch.index.IndexSettingProviders;
 import org.elasticsearch.indices.SystemIndices;
 import org.elasticsearch.indices.TestIndexNameExpressionResolver;
 import org.elasticsearch.test.ESTestCase;
@@ -31,6 +33,7 @@ import org.elasticsearch.test.ESTestCase;
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
 import java.util.List;
+import java.util.Set;
 
 import static org.elasticsearch.cluster.metadata.DataStreamTestHelper.getClusterStateWithDataStreams;
 import static org.elasticsearch.test.LambdaMatchers.transformedItemsMatch;
@@ -173,6 +176,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -205,6 +209,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -257,6 +262,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -302,6 +308,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
 
@@ -349,6 +356,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataGlobalRetention(), nullValue());
@@ -375,6 +383,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             withGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataGlobalRetention(), equalTo(dataGlobalRetention));
@@ -405,6 +414,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
@@ -434,6 +444,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
@@ -469,9 +480,58 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
                         .build()
                 )
             ),
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
         assertThat(response.getDataStreams().get(0).isFailureStoreEffectivelyEnabled(), is(true));
     }
+
+    public void testProvidersAffectMode() {
+        ClusterState state = DataStreamTestHelper.getClusterStateWithDataStreams(
+            List.of(Tuple.tuple("data-stream-1", 2)),
+            List.of(),
+            System.currentTimeMillis(),
+            Settings.EMPTY,
+            0,
+            false,
+            false
+        );
+
+        var req = new GetDataStreamAction.Request(TEST_REQUEST_TIMEOUT, new String[] {});
+        var response = TransportGetDataStreamsAction.innerOperation(
+            state,
+            req,
+            resolver,
+            systemIndices,
+            ClusterSettings.createBuiltInClusterSettings(),
+            dataStreamGlobalRetentionSettings,
+            emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(
+                Set.of(
+                    (
+                        indexName,
+                        dataStreamName,
+                        templateIndexMode,
+                        metadata,
+                        resolvedAt,
+                        indexTemplateAndCreateRequestSettings,
+                        combinedTemplateMappings) -> Settings.builder().put("index.mode", IndexMode.LOOKUP).build()
+                )
+            ),
+            null
+        );
+        assertThat(response.getDataStreams().get(0).getIndexModeName(), equalTo("lookup"));
+        assertThat(
+            response.getDataStreams()
+                .get(0)
+                .getIndexSettingsValues()
+                .values()
+                .stream()
+                .findFirst()
+                .map(GetDataStreamAction.Response.IndexProperties::indexMode)
+                .orElse("bad"),
+            equalTo("standard")
+        );
+    }
 }

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -221,6 +221,7 @@ public class TransportVersions {
     public static final TransportVersion ESQL_DRIVER_TASK_DESCRIPTION_8_19 = def(8_841_0_30);
     public static final TransportVersion ML_INFERENCE_HUGGING_FACE_CHAT_COMPLETION_ADDED_8_19 = def(8_841_0_31);
     public static final TransportVersion FIELD_CAPS_ADD_CLUSTER_ALIAS = def(8_841_0_32);
+    public static final TransportVersion INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM_BACKPORT_8_19 = def(8_841_0_33);
 
     /*
      * STOP! READ THIS FIRST! No, really,

server/src/main/java/org/elasticsearch/action/datastreams/GetDataStreamAction.java

@@ -232,6 +232,7 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
             );
             public static final ParseField FAILURE_STORE_ENABLED = new ParseField("enabled");
             public static final ParseField MAXIMUM_TIMESTAMP = new ParseField("maximum_timestamp");
+            public static final ParseField INDEX_MODE = new ParseField("index_mode");
 
             private final DataStream dataStream;
             private final ClusterHealthStatus dataStreamStatus;
@@ -246,6 +247,8 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
             private final boolean templatePreferIlmValue;
             @Nullable
             private final Long maximumTimestamp;
+            @Nullable
+            private final String indexMode;
 
             public DataStreamInfo(
                 DataStream dataStream,
@@ -256,7 +259,8 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 @Nullable TimeSeries timeSeries,
                 Map<Index, IndexProperties> indexSettingsValues,
                 boolean templatePreferIlmValue,
-                @Nullable Long maximumTimestamp
+                @Nullable Long maximumTimestamp,
+                @Nullable String indexMode
             ) {
                 this.dataStream = dataStream;
                 this.failureStoreEffectivelyEnabled = failureStoreEffectivelyEnabled;
@@ -267,6 +271,7 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 this.indexSettingsValues = indexSettingsValues;
                 this.templatePreferIlmValue = templatePreferIlmValue;
                 this.maximumTimestamp = maximumTimestamp;
+                this.indexMode = indexMode;
             }
 
             @SuppressWarnings("unchecked")
@@ -287,6 +292,9 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                     : Map.of();
                 this.templatePreferIlmValue = in.getTransportVersion().onOrAfter(V_8_11_X) ? in.readBoolean() : true;
                 this.maximumTimestamp = in.getTransportVersion().onOrAfter(TransportVersions.V_8_16_0) ? in.readOptionalVLong() : null;
+                this.indexMode = in.getTransportVersion().onOrAfter(TransportVersions.INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM_BACKPORT_8_19)
+                    ? in.readOptionalString()
+                    : null;
             }
 
             public DataStream getDataStream() {
@@ -329,6 +337,11 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 return maximumTimestamp;
             }
 
+            @Nullable
+            public String getIndexModeName() {
+                return indexMode;
+            }
+
             @Override
             public void writeTo(StreamOutput out) throws IOException {
                 dataStream.writeTo(out);
@@ -348,6 +361,9 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_16_0)) {
                     out.writeOptionalVLong(maximumTimestamp);
                 }
+                if (out.getTransportVersion().onOrAfter(TransportVersions.INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM_BACKPORT_8_19)) {
+                    out.writeOptionalString(indexMode);
+                }
             }
 
             @Override
@@ -400,6 +416,9 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 if (this.maximumTimestamp != null) {
                     builder.field(MAXIMUM_TIMESTAMP.getPreferredName(), this.maximumTimestamp);
                 }
+                if (this.indexMode != null) {
+                    builder.field(INDEX_MODE.getPreferredName(), indexMode);
+                }
                 addAutoShardingEvent(builder, params, dataStream.getAutoShardingEvent());
                 if (timeSeries != null) {
                     builder.startObject(TIME_SERIES.getPreferredName());
@@ -455,6 +474,7 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                                 builder.field(ILM_POLICY_FIELD.getPreferredName(), indexProperties.ilmPolicyName());
                             }
                         }
+                        builder.field(INDEX_MODE.getPreferredName(), indexProperties.indexMode);
                     }
 
                     builder.endObject();
@@ -515,7 +535,8 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                     && Objects.equals(ilmPolicyName, that.ilmPolicyName)
                     && Objects.equals(timeSeries, that.timeSeries)
                     && Objects.equals(indexSettingsValues, that.indexSettingsValues)
-                    && Objects.equals(maximumTimestamp, that.maximumTimestamp);
+                    && Objects.equals(maximumTimestamp, that.maximumTimestamp)
+                    && Objects.equals(indexMode, that.indexMode);
             }
 
             @Override
@@ -529,7 +550,8 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                     timeSeries,
                     indexSettingsValues,
                     templatePreferIlmValue,
-                    maximumTimestamp
+                    maximumTimestamp,
+                    indexMode
                 );
             }
         }
@@ -566,9 +588,18 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
          * Encapsulates the configured properties we want to display for each backing index.
          * They'll usually be settings values, but could also be additional properties derived from settings.
          */
-        public record IndexProperties(boolean preferIlm, @Nullable String ilmPolicyName, ManagedBy managedBy) implements Writeable {
+        public record IndexProperties(boolean preferIlm, @Nullable String ilmPolicyName, ManagedBy managedBy, @Nullable String indexMode)
+            implements
+                Writeable {
             public IndexProperties(StreamInput in) throws IOException {
-                this(in.readBoolean(), in.readOptionalString(), in.readEnum(ManagedBy.class));
+                this(
+                    in.readBoolean(),
+                    in.readOptionalString(),
+                    in.readEnum(ManagedBy.class),
+                    in.getTransportVersion().onOrAfter(TransportVersions.INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM_BACKPORT_8_19)
+                        ? in.readOptionalString()
+                        : "unknown"
+                );
             }
 
             @Override
@@ -576,6 +607,9 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                 out.writeBoolean(preferIlm);
                 out.writeOptionalString(ilmPolicyName);
                 out.writeEnum(managedBy);
+                if (out.getTransportVersion().onOrAfter(TransportVersions.INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM_BACKPORT_8_19)) {
+                    out.writeOptionalString(indexMode);
+                }
             }
         }
 

server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java

@@ -91,6 +91,9 @@ public class MetadataIndexTemplateService {
 
     public static final String DEFAULT_TIMESTAMP_FIELD = "@timestamp";
     public static final CompressedXContent DEFAULT_TIMESTAMP_MAPPING_WITHOUT_ROUTING;
+    // Names used for validating templates when we do not know the index or data stream name
+    public static final String VALIDATE_INDEX_NAME = "validate-index-name";
+    public static final String VALIDATE_DATA_STREAM_NAME = "validate-data-stream-name";
 
     private static final CompressedXContent DEFAULT_TIMESTAMP_MAPPING_WITH_ROUTING;
 
@@ -708,8 +711,8 @@ public class MetadataIndexTemplateService {
         var finalSettings = Settings.builder();
         for (var provider : indexSettingProviders) {
             var newAdditionalSettings = provider.getAdditionalIndexSettings(
-                "validate-index-name",
-                indexTemplate.getDataStreamTemplate() != null ? "validate-data-stream-name" : null,
+                VALIDATE_INDEX_NAME,
+                indexTemplate.getDataStreamTemplate() != null ? VALIDATE_DATA_STREAM_NAME : null,
                 metadata.retrieveIndexModeFromTemplate(indexTemplate),
                 currentState.getMetadata(),
                 now,

server/src/test/java/org/elasticsearch/action/datastreams/GetDataStreamActionTests.java

@@ -92,6 +92,7 @@ public class GetDataStreamActionTests extends ESTestCase {
             null,
             Map.of(),
             randomBoolean(),
+            null,
             null
         );
     }

x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/LogsdbIndexModeSettingsProvider.java

@@ -13,6 +13,7 @@ import org.apache.lucene.util.SetOnce;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
+import org.elasticsearch.cluster.metadata.MetadataIndexTemplateService;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.regex.Regex;
@@ -100,7 +101,9 @@ final class LogsdbIndexModeSettingsProvider implements IndexSettingProvider {
     ) {
         Settings.Builder settingsBuilder = null;
         boolean isLogsDB = templateIndexMode == IndexMode.LOGSDB;
-        boolean isTemplateValidation = "validate-index-name".equals(indexName);
+        // This index name is used when validating component and index templates, we should skip this check in that case.
+        // (See MetadataIndexTemplateService#validateIndexTemplateV2(...) method)
+        boolean isTemplateValidation = MetadataIndexTemplateService.VALIDATE_INDEX_NAME.equals(indexName);
 
         // Inject logsdb index mode, based on the logs pattern.
         if (isLogsdbEnabled
@@ -118,8 +121,6 @@ final class LogsdbIndexModeSettingsProvider implements IndexSettingProvider {
         if (mappingHints.hasSyntheticSourceUsage
             && supportFallbackToStoredSource.get()
             && minNodeVersion.get().get().onOrAfter(Version.V_8_17_0)) {
-            // This index name is used when validating component and index templates, we should skip this check in that case.
-            // (See MetadataIndexTemplateService#validateIndexTemplateV2(...) method)
             boolean legacyLicensedUsageOfSyntheticSourceAllowed = isLegacyLicensedUsageOfSyntheticSourceAllowed(
                 templateIndexMode,
                 indexName,
@@ -216,7 +217,7 @@ final class LogsdbIndexModeSettingsProvider implements IndexSettingProvider {
         Settings indexTemplateAndCreateRequestSettings,
         List<CompressedXContent> combinedTemplateMappings
     ) {
-        if ("validate-index-name".equals(indexName)) {
+        if (MetadataIndexTemplateService.VALIDATE_INDEX_NAME.equals(indexName)) {
             // This index name is used when validating component and index templates, we should skip this check in that case.
             // (See MetadataIndexTemplateService#validateIndexTemplateV2(...) method)
             return MappingHints.EMPTY;

x-pack/plugin/logsdb/src/test/java/org/elasticsearch/xpack/logsdb/LogsdbIndexModeSettingsProviderTests.java

@@ -14,6 +14,7 @@ import org.elasticsearch.cluster.metadata.DataStream;
 import org.elasticsearch.cluster.metadata.DataStreamTestHelper;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.metadata.Metadata;
+import org.elasticsearch.cluster.metadata.MetadataIndexTemplateService;
 import org.elasticsearch.cluster.metadata.Template;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
@@ -473,7 +474,7 @@ public class LogsdbIndexModeSettingsProviderTests extends ESTestCase {
     }
 
     public void testValidateIndexName() throws IOException {
-        String indexName = "validate-index-name";
+        String indexName = MetadataIndexTemplateService.VALIDATE_INDEX_NAME;
         String mapping = """
             {
                 "_doc": {