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",
    }
  ]
}
```

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/indices/get-data-stream.asciidoc

@@ -0,0 +1,376 @@
+[role="xpack"]
+[[indices-get-data-stream]]
+=== Get data stream API
+++++
+<titleabbrev>Get data stream</titleabbrev>
+++++
+
+.New API reference
+[sidebar]
+--
+For the most up-to-date API details, refer to {api-es}/group/endpoint-data-stream[Data stream APIs].
+--
+
+Retrieves information about one or more <<data-streams,data streams>>.
+See <<get-info-about-data-stream>>.
+
+////
+[source,console]
+----
+PUT /_ilm/policy/my-lifecycle-policy
+{
+  "policy": {
+    "phases": {
+      "hot": {
+        "actions": {
+          "rollover": {
+            "max_primary_shard_size": "25GB"
+          }
+        }
+      },
+      "delete": {
+        "min_age": "30d",
+        "actions": {
+          "delete": {}
+        }
+      }
+    }
+  }
+}
+
+PUT /_index_template/my-index-template
+{
+  "index_patterns": [ "my-data-stream*" ],
+  "data_stream": {},
+  "template": {
+    "settings": {
+      "index.lifecycle.name": "my-lifecycle-policy"
+    }
+  },
+  "_meta": {
+    "my-meta-field": "foo"
+  }
+}
+
+PUT /_data_stream/my-data-stream
+
+POST /my-data-stream/_rollover
+
+PUT /_data_stream/my-data-stream-two
+
+DELETE /_data_stream/my-data-stream*/_lifecycle
+----
+// TESTSETUP
+////
+
+////
+[source,console]
+----
+DELETE /_data_stream/*
+DELETE /_index_template/*
+DELETE /_ilm/policy/my-lifecycle-policy
+----
+// TEARDOWN
+////
+
+[source,console]
+----
+GET /_data_stream/my-data-stream
+----
+
+[[get-data-stream-api-request]]
+==== {api-request-title}
+
+`GET /_data_stream/<data-stream>`
+
+[[get-data-stream-api-prereqs]]
+==== {api-prereq-title}
+
+* If the {es} {security-features} are enabled, you must have the
+`view_index_metadata` or `manage` <<privileges-list-indices,index privilege>>
+for the data stream.
+
+[[get-data-stream-api-path-params]]
+==== {api-path-parms-title}
+
+`<data-stream>`::
+(Optional, string)
+Comma-separated list of data stream names used to limit the request. Wildcard
+(`*`) expressions are supported. If omitted, all data streams will be
+returned.
+
+[role="child_attributes"]
+[[get-data-stream-api-query-parms]]
+==== {api-query-parms-title}
+
+include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=ds-expand-wildcards]
++
+Defaults to `open`.
+
+`include_defaults`::
+(Optional, Boolean) Functionality in preview:[]. If `true`, return all default settings in the response.
+Defaults to `false`.
+
+`verbose`::
+(Optional, Boolean). If `true`, Returns the `maximum_timestamp` corresponding to the `@timestamp` field for documents in the data stream.
+Defaults to `false`.
+
+[role="child_attributes"]
+[[get-data-stream-api-response-body]]
+==== {api-response-body-title}
+
+`data_streams`::
+(array of objects)
+Contains information about retrieved data streams.
++
+.Properties of objects in `data_streams`
+[%collapsible%open]
+====
+`name`::
+(string)
+Name of the data stream.
+
+`timestamp_field`::
+(object)
+Contains information about the data stream's `@timestamp` field.
++
+.Properties of `timestamp_field`
+[%collapsible%open]
+=====
+`name`::
+(string)
+Name of the data stream's timestamp field, which must be `@timestamp`. The
+`@timestamp` field must be included in every document indexed to the data
+stream.
+=====
+
+`indices`::
+(array of objects)
+Array of objects containing information about the data stream's backing
+indices.
++
+The last item in this array contains information about the stream's current
+<<data-stream-write-index,write index>>.
++
+.Properties of `indices` objects
+[%collapsible%open]
+=====
+`index_name`::
+(string)
+Name of the backing index. For naming conventions, see
+<<data-streams-generation>>.
+
+`index_uuid`::
+(string)
+Universally unique identifier (UUID) for the index.
+
+`prefer_ilm`::
+(boolean)
+Functionality in preview:[]. Indicates if this index is configured to prefer {ilm}
+when both {ilm-cap} and <<data-stream-lifecycle, Data stream lifecycle>> are configured to
+manage this index.
+
+`managed_by`::
+(string)
+Functionality in preview:[]. Indicates the system that managed this index.
+=====
+
+`generation`::
+(integer)
+Current <<data-streams-generation,generation>> for the data stream. This number
+acts as a cumulative count of the stream's rollovers, starting at `1`.
+
+`_meta`::
+(object)
+Custom metadata for the stream, copied from the `_meta` object of the
+stream's matching <<create-index-template,index template>>. If empty,
+the response omits this property.
+
+`status`::
+(string)
+<<cluster-health,Health status>> of the data stream.
++
+This health status is based on the state of the primary and replica shards of
+the stream's backing indices.
++
+.Values for `status`
+[%collapsible%open]
+=====
+`GREEN`:::
+All shards are assigned.
+
+`YELLOW`:::
+All primary shards are assigned, but one or more replica shards are
+unassigned.
+
+`RED`:::
+One or more primary shards are unassigned, so some data is unavailable.
+=====
+
+`template`::
+(string)
+Name of the index template used to create the data stream's backing indices.
++
+The template's index pattern must match the name of this data stream. See
+<<create-index-template,create an index template>>.
+
+`ilm_policy`::
+(string)
+Name of the current {ilm-init} lifecycle policy in the stream's matching index
+template. This lifecycle policy is set in the `index.lifecycle.name` setting.
++
+If the template does not include a lifecycle policy, this property is not
+included in the response.
++
+NOTE: A data stream's backing indices may be assigned different lifecycle
+policies. To retrieve the lifecycle policy for individual backing indices,
+use the <<indices-get-settings,get index settings API>>.
+
+`next_generation_managed_by`::
+(string)
+Functionality in preview:[]. Indicates the system that will managed the next generation index
+(i.e. the next data stream write index).
+
+`prefer_ilm`::
+(boolean)
+Functionality in preview:[]. Indicates if the index template used to create the data
+stream's backing indices is configured to prefer {ilm-cap} when both {ilm-cap} and
+<<data-stream-lifecycle, Data stream lifecycle>> are configured to manage this index.
+
+`hidden`::
+(Boolean) If `true`, the data stream is <<multi-hidden,hidden>>.
+
+`system`::
+(Boolean)
+If `true`, the data stream is created and managed by an Elastic stack component
+and cannot be modified through normal user interaction.
+
+`allow_custom_routing`::
+(Boolean)
+If `true`, the data stream this data stream allows custom routing on write request.
+
+`replicated`::
+(Boolean)
+If `true`, the data stream is created and managed by {ccr} and the local
+cluster can not write into this data stream or change its mappings.
+
+`lifecycle`::
+(object)
+Functionality in preview:[]. Contains the configuration for the data stream lifecycle management of this data stream.
++
+.Properties of `lifecycle`
+[%collapsible%open]
+=====
+`data_retention`::
+(string)
+If defined, every document added to this data stream will be stored at least for this time frame. Any time after this
+duration the document could be deleted. When empty, every document in this data stream will be stored indefinitely.
+
+`rollover`::
+(object)
+The conditions which will trigger the rollover of a backing index as configured by the cluster setting
+`cluster.lifecycle.default.rollover`. This property is an implementation detail and it will only be retrieved when the query
+param `include_defaults` is set to `true`. The contents of this field are subject to change.
+=====
+
+`rollover_on_write`::
+(Boolean)
+If `true`, the next write to this data stream will trigger a rollover first and the document will be
+indexed in the new backing index. If the rollover fails the indexing request will fail too.
+====
+
+[[get-data-stream-api-example]]
+==== {api-examples-title}
+
+[source,console]
+----
+GET _data_stream/my-data-stream*
+----
+
+The API returns the following response:
+
+[source,console-result]
+----
+{
+  "data_streams": [
+    {
+      "name": "my-data-stream",
+      "timestamp_field": {
+        "name": "@timestamp"
+      },
+      "indices": [
+        {
+          "index_name": ".ds-my-data-stream-2099.03.07-000001",
+          "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
+          "prefer_ilm": true,
+          "ilm_policy": "my-lifecycle-policy",
+          "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",
+          "index_mode": "standard"
+        }
+      ],
+      "generation": 2,
+      "_meta": {
+        "my-meta-field": "foo"
+      },
+      "status": "GREEN",
+      "index_mode": "standard",
+      "next_generation_managed_by": "Index Lifecycle Management",
+      "prefer_ilm": true,
+      "template": "my-index-template",
+      "ilm_policy": "my-lifecycle-policy",
+      "hidden": false,
+      "system": false,
+      "allow_custom_routing": false,
+      "replicated": false,
+      "rollover_on_write": false
+    },
+    {
+      "name": "my-data-stream-two",
+      "timestamp_field": {
+        "name": "@timestamp"
+      },
+      "indices": [
+        {
+          "index_name": ".ds-my-data-stream-two-2099.03.08-000001",
+          "index_uuid": "3liBu2SYS5axasRt6fUIpA",
+          "prefer_ilm": true,
+          "ilm_policy": "my-lifecycle-policy",
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
+        }
+      ],
+      "generation": 1,
+      "_meta": {
+        "my-meta-field": "foo"
+      },
+      "status": "YELLOW",
+      "index_mode": "standard",
+      "next_generation_managed_by": "Index Lifecycle Management",
+      "prefer_ilm": true,
+      "template": "my-index-template",
+      "ilm_policy": "my-lifecycle-policy",
+      "hidden": false,
+      "system": false,
+      "allow_custom_routing": false,
+      "replicated": false,
+      "rollover_on_write": false
+    }
+  ]
+}
+----
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-2099.03.07-000001"/"index_name": $body.data_streams.0.indices.0.index_name/]
+// TESTRESPONSE[s/"index_uuid": "xCEhwsp8Tey0-FLNFYVwSg"/"index_uuid": $body.data_streams.0.indices.0.index_uuid/]
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-2099.03.08-000002"/"index_name": $body.data_streams.0.indices.1.index_name/]
+// TESTRESPONSE[s/"index_uuid": "PA_JquKGSiKcAKBA8DJ5gw"/"index_uuid": $body.data_streams.0.indices.1.index_uuid/]
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-two-2099.03.08-000001"/"index_name": $body.data_streams.1.indices.0.index_name/]
+// TESTRESPONSE[s/"index_uuid": "3liBu2SYS5axasRt6fUIpA"/"index_uuid": $body.data_streams.1.indices.0.index_uuid/]
+// TESTRESPONSE[s/"status": "GREEN"/"status": "YELLOW"/]
+// TESTRESPONSE[s/"replicated": false/"replicated": false,"failure_store":{"enabled": false, "indices": [], "rollover_on_write": true}/]

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

@@ -24,6 +24,7 @@ import org.elasticsearch.cluster.ProjectState;
 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;
@@ -40,6 +41,9 @@ 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;
@@ -53,6 +57,7 @@ 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;
 
@@ -68,6 +73,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
     private final ClusterSettings clusterSettings;
     private final DataStreamGlobalRetentionSettings globalRetentionSettings;
     private final DataStreamFailureStoreSettings dataStreamFailureStoreSettings;
+    private final IndexSettingProviders indexSettingProviders;
     private final Client client;
 
     @Inject
@@ -81,6 +87,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
         SystemIndices systemIndices,
         DataStreamGlobalRetentionSettings globalRetentionSettings,
         DataStreamFailureStoreSettings dataStreamFailureStoreSettings,
+        IndexSettingProviders indexSettingProviders,
         Client client
     ) {
         super(
@@ -99,6 +106,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
         this.globalRetentionSettings = globalRetentionSettings;
         clusterSettings = clusterService.getClusterSettings();
         this.dataStreamFailureStoreSettings = dataStreamFailureStoreSettings;
+        this.indexSettingProviders = indexSettingProviders;
         this.client = new OriginSettingClient(client, "stack");
     }
 
@@ -131,6 +139,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
                             clusterSettings,
                             globalRetentionSettings,
                             dataStreamFailureStoreSettings,
+                            indexSettingProviders,
                             maxTimestamps
                         )
                     );
@@ -151,12 +160,43 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
                     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(
+        ProjectState 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(
         ProjectState state,
         GetDataStreamAction.Request request,
@@ -165,6 +205,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
         ClusterSettings clusterSettings,
         DataStreamGlobalRetentionSettings globalRetentionSettings,
         DataStreamFailureStoreSettings dataStreamFailureStoreSettings,
+        IndexSettingProviders indexSettingProviders,
         @Nullable Map<String, Long> maxTimestamps
     ) {
         List<DataStream> dataStreams = getDataStreams(state.metadata(), indexNameExpressionResolver, request);
@@ -177,6 +218,7 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
             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;
@@ -186,6 +228,15 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
                         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 {
@@ -193,6 +244,15 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
                 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(
@@ -285,7 +345,9 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
                     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()
                 )
             );
         }
@@ -314,7 +376,11 @@ public class TransportGetDataStreamsAction extends TransportMasterNodeReadProjec
             } 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

@@ -91,13 +91,13 @@ 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(
@@ -109,6 +109,7 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 null,
                 indexSettingsValues,
                 false,
+                null,
                 null
             );
             Response response = new Response(List.of(dataStreamInfo));
@@ -195,13 +196,13 @@ 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(
@@ -213,6 +214,7 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                 null,
                 indexSettingsValues,
                 false,
+                null,
                 null
             );
             Response response = new Response(List.of(dataStreamInfo));
@@ -309,7 +311,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
                         new Response.IndexProperties(
                             randomBoolean(),
                             randomAlphaOfLengthBetween(50, 100),
-                            randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE
+                            randomBoolean() ? ManagedBy.ILM : ManagedBy.LIFECYCLE,
+                            null
                         )
                     )
             );
@@ -328,7 +331,8 @@ public class GetDataStreamsResponseTests extends AbstractWireSerializingTestCase
             timeSeries,
             indexSettings,
             templatePreferIlm,
-            maximumTimestamp
+            maximumTimestamp,
+            null
         );
     }
 
@@ -349,7 +353,8 @@ 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
                 )
             );
         }
@@ -367,7 +372,8 @@ 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

@@ -24,7 +24,9 @@ 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;
@@ -32,6 +34,7 @@ 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;
@@ -181,6 +184,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -213,6 +217,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -266,6 +271,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(
@@ -307,6 +313,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
 
@@ -341,6 +348,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getGlobalRetention(), nullValue());
@@ -367,6 +375,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             withGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getGlobalRetention(), equalTo(globalRetention));
@@ -394,6 +403,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
@@ -423,6 +433,7 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
             ClusterSettings.createBuiltInClusterSettings(),
             dataStreamGlobalRetentionSettings,
             emptyDataStreamFailureStoreSettings,
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
@@ -457,9 +468,63 @@ public class TransportGetDataStreamsActionTests extends ESTestCase {
                         .build()
                 )
             ),
+            new IndexSettingProviders(Set.of()),
             null
         );
         assertThat(response.getDataStreams(), hasSize(1));
         assertThat(response.getDataStreams().getFirst().isFailureStoreEffectivelyEnabled(), is(true));
     }
+
+    public void testProvidersAffectMode() {
+        ClusterState state;
+        var projectId = randomProjectIdOrDefault();
+        {
+            state = DataStreamTestHelper.getClusterStateWithDataStreams(
+                projectId,
+                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.projectState(projectId),
+            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().getFirst().getIndexModeName(), equalTo("lookup"));
+        assertThat(
+            response.getDataStreams()
+                .getFirst()
+                .getIndexSettingsValues()
+                .values()
+                .stream()
+                .findFirst()
+                .map(GetDataStreamAction.Response.IndexProperties::indexMode)
+                .orElse("bad"),
+            equalTo("standard")
+        );
+    }
 }

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

@@ -183,6 +183,7 @@ public class TransportVersions {
     public static final TransportVersion STORED_SCRIPT_CONTENT_LENGTH = def(9_019_0_00);
     public static final TransportVersion JINA_AI_EMBEDDING_TYPE_SUPPORT_ADDED = def(9_020_0_00);
     public static final TransportVersion RE_REMOVE_MIN_COMPATIBLE_SHARD_NODE = def(9_021_0_00);
+    public static final TransportVersion INCLUDE_INDEX_MODE_IN_GET_DATA_STREAM = def(9_022_0_00);
 
     /*
      * 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)
+                    ? 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)) {
+                    out.writeOptionalString(indexMode);
+                }
             }
 
             @Override
@@ -398,6 +414,9 @@ 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());
@@ -441,6 +460,7 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                             builder.field(ILM_POLICY_FIELD.getPreferredName(), indexProperties.ilmPolicyName());
                         }
                         builder.field(MANAGED_BY.getPreferredName(), indexProperties.managedBy.displayValue);
+                        builder.field(INDEX_MODE.getPreferredName(), indexProperties.indexMode);
                     }
                     builder.endObject();
                 }
@@ -500,7 +520,8 @@ 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
@@ -514,7 +535,8 @@ public class GetDataStreamAction extends ActionType<GetDataStreamAction.Response
                     timeSeries,
                     indexSettingsValues,
                     templatePreferIlmValue,
-                    maximumTimestamp
+                    maximumTimestamp,
+                    indexMode
                 );
             }
         }
@@ -551,9 +573,18 @@ 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)
+                        ? in.readOptionalString()
+                        : "unknown"
+                );
             }
 
             @Override
@@ -561,6 +592,9 @@ 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)) {
+                    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;
 
@@ -714,8 +717,8 @@ public class MetadataIndexTemplateService {
         var finalSettings = Settings.builder();
         for (var provider : indexSettingProviders) {
             var newAdditionalSettings = provider.getAdditionalIndexSettings(
-                "validate-index-name",
+                VALIDATE_INDEX_NAME,
-                indexTemplate.getDataStreamTemplate() != null ? "validate-data-stream-name" : null,
+                indexTemplate.getDataStreamTemplate() != null ? VALIDATE_DATA_STREAM_NAME : null,
                 projectMetadata.retrieveIndexModeFromTemplate(indexTemplate),
                 projectMetadata,
                 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

@@ -12,6 +12,7 @@ import org.apache.logging.log4j.Logger;
 import org.apache.lucene.util.SetOnce;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.cluster.metadata.MetadataIndexTemplateService;
 import org.elasticsearch.cluster.metadata.ProjectMetadata;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.compress.CompressedXContent;
@@ -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.ProjectMetadata;
 import org.elasticsearch.cluster.metadata.Template;
 import org.elasticsearch.common.compress.CompressedXContent;
@@ -475,7 +476,7 @@ public class LogsdbIndexModeSettingsProviderTests extends ESTestCase {
     }
 
     public void testValidateIndexName() throws IOException {
-        String indexName = "validate-index-name";
+        String indexName = MetadataIndexTemplateService.VALIDATE_INDEX_NAME;
         String mapping = """
             {
                 "_doc": {