Prohibit clone, shrink, and split on a data stream's write index

rest-api-spec/src/main/resources/rest-api-spec/test/indices.clone/10_basic.yml

@@ -109,3 +109,47 @@ setup:
           settings:
             index.number_of_replicas: 0
             index.number_of_shards: 6
+
+---
+"Prohibit clone on data stream's write index":
+  - skip:
+      version: " - 7.99.99"
+      reason: needs backport
+      features: allowed_warnings
+
+  - do:
+      allowed_warnings:
+        - "index template [my-template1] has index patterns [simple-data-stream1] matching patterns from existing older templates [global] with patterns (global => [*]); this template [my-template1] will take precedence during new index creation"
+      indices.put_index_template:
+        name: my-template1
+        body:
+          index_patterns: [simple-data-stream1]
+          template:
+            mappings:
+              properties:
+                '@timestamp':
+                  type: date
+          data_stream:
+            timestamp_field: '@timestamp'
+
+  - do:
+      indices.create_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged
+
+  - do:
+      catch: bad_request
+      indices.clone:
+        index: ".ds-simple-data-stream1-000001"
+        target: "target"
+        wait_for_active_shards: 1
+        master_timeout: 10s
+        body:
+          settings:
+            index.number_of_replicas: 0
+            index.number_of_shards: 2
+
+  - do:
+      indices.delete_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged

rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml

@@ -81,3 +81,46 @@
   - match: { _type:    _doc   }
   - match: { _id:      "1"     }
   - match: { _source:  { foo: "hello world" } }
+
+---
+"Prohibit shrink on data stream's write index":
+  - skip:
+      version: " - 7.99.99"
+      reason: needs backport
+      features: allowed_warnings
+
+  - do:
+      allowed_warnings:
+        - "index template [my-template1] has index patterns [simple-data-stream1] matching patterns from existing older templates [global] with patterns (global => [*]); this template [my-template1] will take precedence during new index creation"
+      indices.put_index_template:
+        name: my-template1
+        body:
+          index_patterns: [simple-data-stream1]
+          template:
+            mappings:
+              properties:
+                '@timestamp':
+                  type: date
+          data_stream:
+            timestamp_field: '@timestamp'
+
+  - do:
+      indices.create_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged
+
+  - do:
+      catch: bad_request
+      indices.shrink:
+        index: ".ds-simple-data-stream1-000001"
+        target: "target"
+        wait_for_active_shards: 1
+        master_timeout: 10s
+        body:
+          settings:
+            index.number_of_replicas: 0
+
+  - do:
+      indices.delete_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged

rest-api-spec/src/main/resources/rest-api-spec/test/indices.split/10_basic.yml

@@ -221,3 +221,47 @@ setup:
           settings:
             index.number_of_replicas: 0
             index.number_of_shards: 6
+
+---
+"Prohibit split on data stream's write index":
+  - skip:
+      version: " - 7.99.99"
+      reason: needs backport
+      features: allowed_warnings
+
+  - do:
+      allowed_warnings:
+        - "index template [my-template1] has index patterns [simple-data-stream1] matching patterns from existing older templates [global] with patterns (global => [*]); this template [my-template1] will take precedence during new index creation"
+      indices.put_index_template:
+        name: my-template1
+        body:
+          index_patterns: [simple-data-stream1]
+          template:
+            mappings:
+              properties:
+                '@timestamp':
+                  type: date
+          data_stream:
+            timestamp_field: '@timestamp'
+
+  - do:
+      indices.create_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged
+
+  - do:
+      catch: bad_request
+      indices.split:
+        index: ".ds-simple-data-stream1-000001"
+        target: "target"
+        wait_for_active_shards: 1
+        master_timeout: 10s
+        body:
+          settings:
+            index.number_of_replicas: 0
+            index.number_of_shards: 4
+
+  - do:
+      indices.delete_data_stream:
+        name: simple-data-stream1
+  - is_true: acknowledged

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

@@ -1131,6 +1131,15 @@ public class MetadataCreateIndexService {
         if (sourceMetadata == null) {
             throw new IndexNotFoundException(sourceIndex);
         }
+
+        IndexAbstraction source = state.metadata().getIndicesLookup().get(sourceIndex);
+        assert source != null;
+        if (source.getParentDataStream() != null &&
+            source.getParentDataStream().getWriteIndex().getIndex().equals(sourceMetadata.getIndex())) {
+            throw new IllegalArgumentException(String.format(Locale.ROOT, "cannot resize the write index [%s] for data stream [%s]",
+                sourceIndex, source.getParentDataStream().getName()));
+        }
+
         // ensure index is read-only
         if (state.blocks().indexBlocked(ClusterBlockLevel.WRITE, sourceIndex) == false) {
             throw new IllegalStateException("index " + sourceIndex + " must be read-only to resize index. use \"index.blocks.write=true\"");