Adding support for index.number_of_replicas to data stream settings

masseyke · masseyke · commit 65774f82a9d8 · 2025-08-12T10:34:35.000-05:00
diff --git a/modules/data-streams/src/main/java/org/elasticsearch/datastreams/action/TransportUpdateDataStreamSettingsAction.java b/modules/data-streams/src/main/java/org/elasticsearch/datastreams/action/TransportUpdateDataStreamSettingsAction.java
@@ -54,7 +54,8 @@ public class TransportUpdateDataStreamSettingsAction extends TransportMasterNode
     UpdateDataStreamSettingsAction.Request,
     UpdateDataStreamSettingsAction.Response> {
     private static final Logger logger = LogManager.getLogger(TransportUpdateDataStreamSettingsAction.class);
-    private static final Set<String> APPLY_TO_BACKING_INDICES = Set.of(
+    private static final Set<String> APPLY_TO_WRITE_INDEX = Set.of("index.number_of_replicas");
+    private static final Set<String> APPLY_TO_ALL_BACKING_INDICES = Set.of(
         "index.lifecycle.name",
         IndexSettings.PREFER_ILM,
         "index.refresh_interval"
@@ -158,7 +159,9 @@ private void updateSingleDataStream(
         logger.debug("updating settings for {}", dataStreamName);
         Set<String> settingsToReject = new HashSet<>();
         for (String settingName : settingsOverrides.keySet()) {
-            if (APPLY_TO_BACKING_INDICES.contains(settingName) == false && APPLY_TO_DATA_STREAM_ONLY.contains(settingName) == false) {
+            if (APPLY_TO_WRITE_INDEX.contains(settingName) == false
+                && APPLY_TO_ALL_BACKING_INDICES.contains(settingName) == false
+                && APPLY_TO_DATA_STREAM_ONLY.contains(settingName) == false) {
                 settingsToReject.add(settingName);
             }
         }
@@ -223,19 +226,26 @@ private void updateSettingsOnIndices(
         TimeValue ackTimeout,
         ActionListener<UpdateDataStreamSettingsAction.DataStreamSettingsResponse> listener
     ) {
-        Map<String, Object> settingsToApply = new HashMap<>();
+        Map<String, Object> settingsToApplyToNonWriteIndices = new HashMap<>();
+        Map<String, Object> settingsToApplyToWriteIndex = new HashMap<>();
         List<String> appliedToDataStreamOnly = new ArrayList<>();
+        List<String> appliedToDataStreamAndWriteIndexOnly = new ArrayList<>();
         List<String> appliedToDataStreamAndBackingIndices = new ArrayList<>();
         Settings effectiveSettings = dataStream.getEffectiveSettings(projectResolver.getProjectMetadata(clusterService.state()));
         for (String settingName : requestSettings.keySet()) {
-            if (APPLY_TO_BACKING_INDICES.contains(settingName)) {
-                settingsToApply.put(settingName, effectiveSettings.get(settingName));
+            if (APPLY_TO_WRITE_INDEX.contains(settingName)) {
+                settingsToApplyToWriteIndex.put(settingName, effectiveSettings.get(settingName));
+                appliedToDataStreamAndWriteIndexOnly.add(settingName);
+            } else if (APPLY_TO_ALL_BACKING_INDICES.contains(settingName)) {
+                settingsToApplyToWriteIndex.put(settingName, effectiveSettings.get(settingName));
+                settingsToApplyToNonWriteIndices.put(settingName, effectiveSettings.get(settingName));
                 appliedToDataStreamAndBackingIndices.add(settingName);
             } else if (APPLY_TO_DATA_STREAM_ONLY.contains(settingName)) {
                 appliedToDataStreamOnly.add(settingName);
             }
         }
         final List<Index> concreteIndices = dataStream.getIndices();
+        final Index writeIndex = dataStream.getWriteIndex();
         final List<UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndexSettingError> indexSettingErrors = new ArrayList<>();
 
         CountDownActionListener indexCountDownListener = new CountDownActionListener(
@@ -250,6 +260,7 @@ private void updateSettingsOnIndices(
                         settingsFilter.filter(effectiveSettings),
                         new UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult(
                             appliedToDataStreamOnly,
+                            appliedToDataStreamAndWriteIndexOnly,
                             appliedToDataStreamAndBackingIndices,
                             indexSettingErrors
                         )
@@ -259,11 +270,13 @@ private void updateSettingsOnIndices(
         );
 
         indexCountDownListener.onResponse(null); // handles the case where there were zero indices
-        Settings applyToIndexSettings = builder().loadFromMap(settingsToApply).build();
+        Settings applyToNonWriteIndexSettings = builder().loadFromMap(settingsToApplyToNonWriteIndices).build();
+        Settings applyToWriteIndexSettings = builder().loadFromMap(settingsToApplyToWriteIndex).build();
         for (Index index : concreteIndices) {
+            Settings settings = index.equals(writeIndex) ? applyToWriteIndexSettings : applyToNonWriteIndexSettings;
             updateSettingsOnSingleIndex(
                 index,
-                applyToIndexSettings,
+                settings,
                 dryRun,
                 masterNodeTimeout,
                 ackTimeout,
diff --git a/modules/data-streams/src/yamlRestTest/resources/rest-api-spec/test/data_stream/240_data_stream_settings.yml b/modules/data-streams/src/yamlRestTest/resources/rest-api-spec/test/data_stream/240_data_stream_settings.yml
@@ -495,3 +495,98 @@ setup:
         index: my-component-only-data-stream-1
   - match: { .$idx0name.settings.index.lifecycle.name: "my-policy" }
   - match: { .$idx0name.settings.index.lifecycle.prefer_ilm: null }
+
+---
+"Test write index only setting":
+  - requires:
+      cluster_features: [ "logs_stream" ]
+      reason: requires setting 'logs_stream' to get or set data stream settings
+  - do:
+      allowed_warnings:
+        - "index template [my-template] has index patterns [my-data-stream-*] matching patterns from existing older templates [global] with patterns (global => [*]); this template [my-template] will take precedence during new index creation"
+      indices.put_index_template:
+        name: my-template
+        body:
+          index_patterns: [ my-data-stream-* ]
+          data_stream: { }
+          template:
+            settings:
+              number_of_replicas: 0
+              lifecycle.name: my-policy
+
+  - do:
+      indices.create_data_stream:
+        name: my-data-stream-1
+
+  - do:
+      cluster.health:
+        index: "my-data-stream-1"
+        wait_for_status: green
+
+  - do:
+      indices.get_data_stream_settings:
+        name: my-data-stream-1
+  - match: { data_streams.0.name: my-data-stream-1 }
+  - match: { data_streams.0.settings: {} }
+  - match: { data_streams.0.effective_settings.index.number_of_shards: null }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "0" }
+
+  - do:
+      indices.rollover:
+        alias: "my-data-stream-1"
+
+  - do:
+      cluster.health:
+        index: "my-data-stream-1"
+        wait_for_status: green
+
+  - do:
+      indices.put_data_stream_settings:
+        name: my-data-stream-1
+        body:
+          index:
+            number_of_replicas: 1
+  - match: { data_streams.0.name: my-data-stream-1 }
+  - match: { data_streams.0.applied_to_data_stream: true }
+  - match: { data_streams.0.index_settings_results.applied_to_data_stream_only: []}
+  - match: { data_streams.0.index_settings_results.applied_to_data_stream_and_backing_indices: []}
+  - length: { data_streams.0.index_settings_results.applied_to_data_stream_and_write_index: 1  }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "1" }
+
+  - do:
+      indices.rollover:
+        alias: "my-data-stream-1"
+
+  - do:
+      cluster.health:
+        index: "my-data-stream-1"
+        wait_for_status: yellow
+
+  - do:
+      indices.get_data_stream_settings:
+        name: my-data-stream-1
+  - match: { data_streams.0.name: my-data-stream-1 }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "1" }
+
+  - do:
+      indices.get_data_stream:
+        name: my-data-stream-1
+  - match: { data_streams.0.name: my-data-stream-1 }
+  - match: { data_streams.0.settings.index.number_of_replicas: "1" }
+  - match: { data_streams.0.effective_settings: null }
+
+  - do:
+      indices.get_data_stream:
+        name: my-data-stream-1
+  - set: { data_streams.0.indices.0.index_name: idx0name }
+  - set: { data_streams.0.indices.1.index_name: idx1name }
+  - set: { data_streams.0.indices.2.index_name: idx2name }
+
+  # We expect that index.number_of_replicas only gets updated on the current write index and any future indices. We have
+  # done one rollover since setting the setting, so it ought to be updated in the two most recent indices only:
+  - do:
+      indices.get_settings:
+        index: my-data-stream-1
+  - match: { .$idx0name.settings.index.number_of_replicas: "0" }
+  - match: { .$idx1name.settings.index.number_of_replicas: "1" }
+  - match: { .$idx2name.settings.index.number_of_replicas: "1" }
diff --git a/server/src/main/java/org/elasticsearch/TransportVersions.java b/server/src/main/java/org/elasticsearch/TransportVersions.java
@@ -363,6 +363,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion INDEX_TEMPLATE_TRACKING_INFO = def(9_136_0_00);
     public static final TransportVersion EXTENDED_SNAPSHOT_STATS_IN_NODE_INFO = def(9_137_0_00);
     public static final TransportVersion SIMULATE_INGEST_MAPPING_MERGE_TYPE = def(9_138_0_00);
+    public static final TransportVersion DATA_STREAM_WRITE_INDEX_ONLY_SETTINGS = def(9_139_0_00);
 
     /*
      * STOP! READ THIS FIRST! No, really,
diff --git a/server/src/main/java/org/elasticsearch/action/datastreams/UpdateDataStreamSettingsAction.java b/server/src/main/java/org/elasticsearch/action/datastreams/UpdateDataStreamSettingsAction.java
@@ -232,19 +232,28 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
 
         public record IndicesSettingsResult(
             List<String> appliedToDataStreamOnly,
+            List<String> appliedToDataStreamAndWriteIndex,
             List<String> appliedToDataStreamAndBackingIndices,
             List<IndexSettingError> indexSettingErrors
         ) implements ToXContent, Writeable {
 
-            public static final IndicesSettingsResult EMPTY = new IndicesSettingsResult(List.of(), List.of(), List.of());
+            public static final IndicesSettingsResult EMPTY = new IndicesSettingsResult(List.of(), List.of(), List.of(), List.of());
 
             public IndicesSettingsResult(StreamInput in) throws IOException {
-                this(in.readStringCollectionAsList(), in.readStringCollectionAsList(), in.readCollectionAsList(IndexSettingError::new));
+                this(
+                    in.readStringCollectionAsList(),
+                    in.getTransportVersion().onOrAfter(TransportVersions.DATA_STREAM_WRITE_INDEX_ONLY_SETTINGS)
+                        ? in.readStringCollectionAsList()
+                        : List.of(),
+                    in.readStringCollectionAsList(),
+                    in.readCollectionAsList(IndexSettingError::new)
+                );
             }
 
             @Override
             public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
                 builder.field("applied_to_data_stream_only", appliedToDataStreamOnly);
+                builder.field("applied_to_data_stream_and_write_index", appliedToDataStreamAndWriteIndex);
                 builder.field("applied_to_data_stream_and_backing_indices", appliedToDataStreamAndBackingIndices);
                 if (indexSettingErrors.isEmpty() == false) {
                     builder.field("errors", indexSettingErrors);
@@ -255,6 +264,9 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             @Override
             public void writeTo(StreamOutput out) throws IOException {
                 out.writeStringCollection(appliedToDataStreamOnly);
+                if (out.getTransportVersion().onOrAfter(TransportVersions.DATA_STREAM_WRITE_INDEX_ONLY_SETTINGS)) {
+                    out.writeStringCollection(appliedToDataStreamAndWriteIndex);
+                }
                 out.writeStringCollection(appliedToDataStreamAndBackingIndices);
                 out.writeCollection(indexSettingErrors, (out1, value) -> value.writeTo(out1));
             }
diff --git a/server/src/test/java/org/elasticsearch/action/datastreams/UpdateDataStreamSettingsActionResponseTests.java b/server/src/test/java/org/elasticsearch/action/datastreams/UpdateDataStreamSettingsActionResponseTests.java
@@ -39,6 +39,7 @@ public void testToXContent() throws IOException {
         Map<String, String> dataStream1Settings = Map.of("setting1", "value1", "setting2", "value2");
         Map<String, String> dataStream1EffectiveSettings = Map.of("setting1", "value1", "setting2", "value2", "setting3", "value3");
         List<String> dataStream1AppliedToDataStreamOnly = randomList(10, () -> randomAlphanumericOfLength(10));
+        List<String> dataStream1AppliedToWriteIndexOnly = randomList(10, () -> randomAlphanumericOfLength(10));
         List<String> dataStream1AppliedToBackingIndices = randomList(10, () -> randomAlphanumericOfLength(10));
         List<IndexSettingError> dataStream1IndexErrors = randomList(
             10,
@@ -65,6 +66,7 @@ public void testToXContent() throws IOException {
                 Settings.builder().loadFromMap(dataStream1EffectiveSettings).build(),
                 new UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult(
                     dataStream1AppliedToDataStreamOnly,
+                    dataStream1AppliedToWriteIndexOnly,
                     dataStream1AppliedToBackingIndices,
                     dataStream1IndexErrors
                 )
@@ -78,6 +80,7 @@ public void testToXContent() throws IOException {
                 Settings.builder().loadFromMap(dataStream2EffectiveSettings).build(),
                 new UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult(
                     dataStream2AppliedToDataStreamOnly,
+                    dataStream1AppliedToWriteIndexOnly,
                     dataStream2AppliedToBackingIndices,
                     dataStream2IndexErrors
                 )
@@ -110,6 +113,7 @@ public void testToXContent() throws IOException {
                                 dataStream1Settings,
                                 dataStream1EffectiveSettings,
                                 dataStream1AppliedToDataStreamOnly,
+                                dataStream1AppliedToWriteIndexOnly,
                                 dataStream1AppliedToBackingIndices,
                                 dataStream1IndexErrors
                             ),
@@ -120,6 +124,7 @@ public void testToXContent() throws IOException {
                                 dataStream2Settings,
                                 dataStream2EffectiveSettings,
                                 dataStream2AppliedToDataStreamOnly,
+                                dataStream1AppliedToWriteIndexOnly,
                                 dataStream2AppliedToBackingIndices,
                                 dataStream2IndexErrors
                             )
@@ -137,6 +142,7 @@ private Map<String, Object> buildExpectedMap(
         Map<String, String> settings,
         Map<String, String> effectiveSettings,
         List<String> appliedToDataStreamOnly,
+        List<String> appliedToWriteIndexOnly,
         List<String> appliedToIndices,
         List<IndexSettingError> indexErrors
     ) {
@@ -150,6 +156,7 @@ private Map<String, Object> buildExpectedMap(
         result.put("effective_settings", effectiveSettings);
         Map<String, Object> indexSettingsResults = new HashMap<>();
         indexSettingsResults.put("applied_to_data_stream_only", appliedToDataStreamOnly);
+        indexSettingsResults.put("applied_to_data_stream_and_write_index", appliedToWriteIndexOnly);
         indexSettingsResults.put("applied_to_data_stream_and_backing_indices", appliedToIndices);
         if (indexErrors.isEmpty() == false) {
             indexSettingsResults.put(
@@ -181,6 +188,7 @@ private UpdateDataStreamSettingsAction.DataStreamSettingsResponse randomDataStre
 
     private UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult randomIndicesSettingsResult() {
         return new UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult(
+            randomList(10, () -> randomAlphanumericOfLength(20)),
             randomList(10, () -> randomAlphanumericOfLength(20)),
             randomList(10, () -> randomAlphanumericOfLength(20)),
             randomList(10, this::randomIndexSettingError)
