Freezing an index should increase its index settings version (#37813)

When an index is frozen, two index settings are updated (index.frozen and 
index.search.throttled) but the settings version is left unchanged and does 
not reflect the settings update. This commit change the 
TransportFreezeIndexAction so that it also increases the settings version 
when an index is frozen/unfrozen.

This issue has been caught while working on the replication of closed 
indices (#3388) in which index metadata for a closed index are updated 
to frozen metadata and this specific assertion tripped.

Author: tlrx

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/action/TransportFreezeIndexAction.java

@@ -183,6 +183,7 @@ public ClusterState execute(ClusterState currentState) {
                         throw new IllegalStateException("index [" + index.getName() + "] is not closed");
                     }
                     final IndexMetaData.Builder imdBuilder = IndexMetaData.builder(meta);
+                    imdBuilder.settingsVersion(meta.getSettingsVersion() + 1);
                     final Settings.Builder settingsBuilder =
                         Settings.builder()
                             .put(currentState.metaData().index(index).getSettings())

x-pack/plugin/core/src/test/java/org/elasticsearch/index/engine/FrozenIndexTests.java

@@ -45,6 +45,7 @@
 import static org.elasticsearch.action.support.WriteRequest.RefreshPolicy.IMMEDIATE;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount;
+import static org.hamcrest.Matchers.equalTo;
 
 public class FrozenIndexTests extends ESSingleNodeTestCase {
 
@@ -324,4 +325,19 @@ public void testUnfreezeClosedIndex() throws ExecutionException, InterruptedExce
         assertEquals(IndexMetaData.State.OPEN,
             client().admin().cluster().prepareState().get().getState().metaData().index("idx").getState());
     }
+
+    public void testFreezeIndexIncreasesIndexSettingsVersion() throws ExecutionException, InterruptedException {
+        final String index = "test";
+        createIndex(index, Settings.builder().put("index.number_of_shards", 1).put("index.number_of_replicas", 0).build());
+        client().prepareIndex(index, "_doc").setSource("field", "value").execute().actionGet();
+
+        final long settingsVersion = client().admin().cluster().prepareState().get()
+            .getState().metaData().index(index).getSettingsVersion();
+
+        XPackClient xPackClient = new XPackClient(client());
+        assertAcked(xPackClient.freeze(new TransportFreezeIndexAction.FreezeRequest(index)));
+        assertIndexFrozen(index);
+        assertThat(client().admin().cluster().prepareState().get().getState().metaData().index(index).getSettingsVersion(),
+            equalTo(settingsVersion + 1));
+    }
 }