Adding the ability to unset data stream settings (#129677)

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

@@ -131,7 +131,7 @@ public class TransportUpdateDataStreamSettingsAction extends TransportMasterNode
                         new UpdateDataStreamSettingsAction.DataStreamSettingsResponse(
                             dataStreamName,
                             false,
-                            e.getMessage(),
+                            Strings.hasText(e.getMessage()) ? e.getMessage() : e.toString(),
                             EMPTY,
                             EMPTY,
                             UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult.EMPTY
@@ -222,9 +222,12 @@ public class TransportUpdateDataStreamSettingsAction extends TransportMasterNode
         Map<String, Object> settingsToApply = new HashMap<>();
         List<String> appliedToDataStreamOnly = new ArrayList<>();
         List<String> appliedToDataStreamAndBackingIndices = new ArrayList<>();
+        Settings effectiveSettings = dataStream.getEffectiveSettings(
+            clusterService.state().projectState(projectResolver.getProjectId()).metadata()
+        );
         for (String settingName : requestSettings.keySet()) {
             if (APPLY_TO_BACKING_INDICES.contains(settingName)) {
-                settingsToApply.put(settingName, requestSettings.get(settingName));
+                settingsToApply.put(settingName, effectiveSettings.get(settingName));
                 appliedToDataStreamAndBackingIndices.add(settingName);
             } else if (APPLY_TO_DATA_STREAM_ONLY.contains(settingName)) {
                 appliedToDataStreamOnly.add(settingName);
@@ -242,9 +245,7 @@ public class TransportUpdateDataStreamSettingsAction extends TransportMasterNode
                         true,
                         null,
                         settingsFilter.filter(dataStream.getSettings()),
-                        settingsFilter.filter(
-                            dataStream.getEffectiveSettings(clusterService.state().projectState(projectResolver.getProjectId()).metadata())
-                        ),
+                        settingsFilter.filter(effectiveSettings),
                         new UpdateDataStreamSettingsAction.DataStreamSettingsResponse.IndicesSettingsResult(
                             appliedToDataStreamOnly,
                             appliedToDataStreamAndBackingIndices,

modules/data-streams/src/yamlRestTest/resources/rest-api-spec/test/data_stream/240_data_stream_settings.yml

@@ -299,3 +299,102 @@ setup:
   - match: { .$idx0name.settings.index.lifecycle.name: "my-policy" }
   - match: { .$idx1name.settings.index.number_of_shards: "1" }
   - match: { .$idx1name.settings.index.lifecycle.name: "my-policy" }
+
+---
+"Test null out settings":
+  - 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:
+        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: null }
+
+  - do:
+      indices.put_data_stream_settings:
+        name: my-data-stream-1
+        body:
+          index:
+            number_of_shards: 2
+            lifecycle:
+              name: my-new-policy
+              prefer_ilm: true
+  - 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: [index.number_of_shards]}
+  - length: { data_streams.0.index_settings_results.applied_to_data_stream_and_backing_indices: 2  }
+  - match: { data_streams.0.settings.index.number_of_shards: "2" }
+  - match: { data_streams.0.settings.index.lifecycle.name: "my-new-policy" }
+  - match: { data_streams.0.settings.index.lifecycle.prefer_ilm: "true" }
+  - match: { data_streams.0.effective_settings.index.number_of_shards: "2" }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "0" }
+  - match: { data_streams.0.effective_settings.index.lifecycle.name: "my-new-policy" }
+  - match: { data_streams.0.effective_settings.index.lifecycle.prefer_ilm: "true" }
+
+  - do:
+      indices.put_data_stream_settings:
+        name: my-data-stream-1
+        body:
+          index:
+            number_of_shards: null
+            lifecycle:
+              name: null
+  - 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: [index.number_of_shards]}
+  - length: { data_streams.0.index_settings_results.applied_to_data_stream_and_backing_indices: 1  }
+  - match: { data_streams.0.settings.index.number_of_shards: null }
+  - match: { data_streams.0.settings.index.lifecycle.name: null }
+  - match: { data_streams.0.settings.index.lifecycle.prefer_ilm: "true" }
+  - match: { data_streams.0.effective_settings.index.number_of_shards: null }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "0" }
+  - match: { data_streams.0.effective_settings.index.lifecycle.name: "my-policy" }
+  - match: { data_streams.0.effective_settings.index.lifecycle.prefer_ilm: "true" }
+
+  - 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.index.lifecycle.name: null }
+  - match: { data_streams.0.settings.index.lifecycle.prefer_ilm: "true" }
+  - match: { data_streams.0.effective_settings.index.number_of_shards: null }
+  - match: { data_streams.0.effective_settings.index.number_of_replicas: "0" }
+  - match: { data_streams.0.effective_settings.index.lifecycle.name: "my-policy" }
+
+  - do:
+      indices.get_data_stream:
+        name: my-data-stream-1
+  - set: { data_streams.0.indices.0.index_name: idx0name }
+
+  - do:
+      indices.get_settings:
+        index: my-data-stream-1
+  - match: { .$idx0name.settings.index.number_of_shards: "1" }
+  - match: { .$idx0name.settings.index.lifecycle.name: "my-policy" }
+  - match: { .$idx0name.settings.index.lifecycle.prefer_ilm: "true" }

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

@@ -456,6 +456,15 @@ public class MetadataDataStreamsService {
 
         Template.Builder templateBuilder = Template.builder();
         Settings.Builder mergedSettingsBuilder = Settings.builder().put(existingSettings).put(settingsOverrides);
+        /*
+         * A null value for a setting override means that we remove it from the data stream, and let the value from the template (if any)
+         * be used.
+         */
+        settingsOverrides.keySet().forEach(key -> {
+            if (mergedSettingsBuilder.get(key) == null) {
+                mergedSettingsBuilder.remove(key);
+            }
+        });
         Settings mergedSettings = mergedSettingsBuilder.build();
 
         final ComposableIndexTemplate template = lookupTemplateForDataStream(dataStreamName, projectMetadata);