[CCR] Also copy routing_num_shards from leader to follow index. (#30894)

Bug was introduced when create and follow api was added in #30602

Author: martijnvg

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/CreateAndFollowIndexAction.java

@@ -45,7 +45,6 @@
 import org.elasticsearch.xpack.ccr.CcrSettings;
 
 import java.io.IOException;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 
@@ -247,28 +246,31 @@ protected Boolean newResponse(boolean acknowledged) {
 
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    IndexMetaData currentIndex = currentState.metaData().index(request.getFollowRequest().getFollowIndex());
+                    String followIndex = request.getFollowRequest().getFollowIndex();
+                    IndexMetaData currentIndex = currentState.metaData().index(followIndex);
                     if (currentIndex != null) {
                         throw new ResourceAlreadyExistsException(currentIndex.getIndex());
                     }
 
                     MetaData.Builder mdBuilder = MetaData.builder(currentState.metaData());
-                    IndexMetaData.Builder imdBuilder = IndexMetaData.builder(request.getFollowRequest().getFollowIndex());
+                    IndexMetaData.Builder imdBuilder = IndexMetaData.builder(followIndex);
 
                     // Copy all settings, but overwrite a few settings.
                     Settings.Builder settingsBuilder = Settings.builder();
                     settingsBuilder.put(leaderIndexMetaData.getSettings());
                     // Overwriting UUID here, because otherwise we can't follow indices in the same cluster
                     settingsBuilder.put(IndexMetaData.SETTING_INDEX_UUID, UUIDs.randomBase64UUID());
-                    settingsBuilder.put(IndexMetaData.SETTING_INDEX_PROVIDED_NAME, request.getFollowRequest().getFollowIndex());
+                    settingsBuilder.put(IndexMetaData.SETTING_INDEX_PROVIDED_NAME, followIndex);
                     settingsBuilder.put(CcrSettings.CCR_FOLLOWING_INDEX_SETTING.getKey(), true);
                     imdBuilder.settings(settingsBuilder);
 
                     // Copy mappings from leader IMD to follow IMD
                     for (ObjectObjectCursor<String, MappingMetaData> cursor : leaderIndexMetaData.getMappings()) {
                         imdBuilder.putMapping(cursor.value);
                     }
-                    mdBuilder.put(imdBuilder.build(), false);
+                    imdBuilder.setRoutingNumShards(leaderIndexMetaData.getRoutingNumShards());
+                    IndexMetaData followIMD = imdBuilder.build();
+                    mdBuilder.put(followIMD, false);
 
                     ClusterState.Builder builder = ClusterState.builder(currentState);
                     builder.metaData(mdBuilder.build());
@@ -279,7 +281,10 @@ public ClusterState execute(ClusterState currentState) throws Exception {
                     updatedState = allocationService.reroute(
                         ClusterState.builder(updatedState).routingTable(routingTableBuilder.build()).build(),
                         "follow index [" + request.getFollowRequest().getFollowIndex() + "] created");
-
+    
+                    logger.info("[{}] creating index, cause [ccr_create_and_follow], shards [{}]/[{}]",
+                        followIndex, followIMD.getNumberOfShards(), followIMD.getNumberOfReplicas());
+                    
                     return updatedState;
                 }
             });

x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java

@@ -145,7 +145,6 @@ public void testGetOperationsBasedOnGlobalSequenceId() throws Exception {
         assertThat(operation.id(), equalTo("5"));
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/30227")
     public void testFollowIndex() throws Exception {
         final int numberOfPrimaryShards = randomIntBetween(1, 3);
         final String leaderIndexSettings = getIndexSettings(numberOfPrimaryShards,
@@ -162,6 +161,7 @@ public void testFollowIndex() throws Exception {
         client().execute(CreateAndFollowIndexAction.INSTANCE, createAndFollowRequest).get();
 
         final int firstBatchNumDocs = randomIntBetween(2, 64);
+        logger.info("Indexing [{}] docs as first batch", firstBatchNumDocs);
         for (int i = 0; i < firstBatchNumDocs; i++) {
             final String source = String.format(Locale.ROOT, "{\"f\":%d}", i);
             client().prepareIndex("index1", "doc", Integer.toString(i)).setSource(source, XContentType.JSON).get();
@@ -185,6 +185,7 @@ public void testFollowIndex() throws Exception {
         unfollowIndex("index2");
         client().execute(FollowIndexAction.INSTANCE, followRequest).get();
         final int secondBatchNumDocs = randomIntBetween(2, 64);
+        logger.info("Indexing [{}] docs as second batch", secondBatchNumDocs);
         for (int i = firstBatchNumDocs; i < firstBatchNumDocs + secondBatchNumDocs; i++) {
             final String source = String.format(Locale.ROOT, "{\"f\":%d}", i);
             client().prepareIndex("index1", "doc", Integer.toString(i)).setSource(source, XContentType.JSON).get();
@@ -408,7 +409,7 @@ private void unfollowIndex(String index) throws Exception {
     private CheckedRunnable<Exception> assertExpectedDocumentRunnable(final int value) {
         return () -> {
             final GetResponse getResponse = client().prepareGet("index2", "doc", Integer.toString(value)).get();
-            assertTrue("doc with id [" + value + "] does not exist", getResponse.isExists());
+            assertTrue("Doc with id [" + value + "] is missing", getResponse.isExists());
             assertTrue((getResponse.getSource().containsKey("f")));
             assertThat(getResponse.getSource().get("f"), equalTo(value));
         };