From 51111a81063977c2ac89df79be4aff83bc3bf92f Mon Sep 17 00:00:00 2001
From: Nhat Nguyen <nhat.nguyen@elastic.co>
Date: Mon, 26 Mar 2018 13:56:47 -0400
Subject: [PATCH] CCR: Stop FollowExistingIndexAction after report failure
 (#4111)

We check for the existence of both leader and follower index, then properly
report to the caller. However, we do not return after reporting failure. This
causes the caller receive exception twice: IllegalArgumentException then
NullPointerException. This commit makes sure to stop the action after reporting
failure.
---
 .../ccr/action/FollowExistingIndexAction.java |  2 ++
 .../xpack/ccr/ShardChangesIT.java             | 22 +++++++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
index 0ea6de6fe7b..c200acf9ad7 100644
--- a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
+++ b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
@@ -156,12 +156,14 @@ public class FollowExistingIndexAction extends Action<FollowExistingIndexAction.
                             .index(request.leaderIndex);
                     if (leaderIndexMetadata == null) {
                         listener.onFailure(new IllegalArgumentException("leader index [" + request.leaderIndex + "] does not exist"));
+                        return;
                     }
 
                     IndexMetaData followIndexMetadata = clusterStateResponse.getState().getMetaData()
                             .index(request.followIndex);
                     if (followIndexMetadata == null) {
                         listener.onFailure(new IllegalArgumentException("follow index [" + request.followIndex + "] does not exist"));
+                        return;
                     }
 
                     if (leaderIndexMetadata.getNumberOfShards() != followIndexMetadata.getNumberOfShards()) {
diff --git a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
index 4c12ab5e6f6..0ea0b5c8295 100644
--- a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
+++ b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
@@ -34,15 +34,15 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.index.translog.Translog;
+import org.elasticsearch.persistent.PersistentTasksCustomMetaData;
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.discovery.TestZenDiscovery;
-import org.elasticsearch.xpack.core.XPackSettings;
 import org.elasticsearch.xpack.ccr.action.FollowExistingIndexAction;
 import org.elasticsearch.xpack.ccr.action.ShardChangesAction;
 import org.elasticsearch.xpack.ccr.action.ShardFollowTask;
 import org.elasticsearch.xpack.ccr.action.UnfollowIndexAction;
-import org.elasticsearch.persistent.PersistentTasksCustomMetaData;
+import org.elasticsearch.xpack.core.XPackSettings;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -219,6 +219,24 @@ public class ShardChangesIT extends ESIntegTestCase {
         });
     }
 
+    public void testFollowNonExistentIndex() throws Exception {
+        assertAcked(client().admin().indices().prepareCreate("test-leader").get());
+        assertAcked(client().admin().indices().prepareCreate("test-follower").get());
+        final FollowExistingIndexAction.Request followRequest = new FollowExistingIndexAction.Request();
+        // Leader index does not exist.
+        followRequest.setLeaderIndex("non-existent-leader");
+        followRequest.setFollowIndex("test-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+        // Follower index does not exist.
+        followRequest.setLeaderIndex("test-leader");
+        followRequest.setFollowIndex("non-existent-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+        // Both indices do not exist.
+        followRequest.setLeaderIndex("non-existent-leader");
+        followRequest.setFollowIndex("non-existent-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+    }
+
     private CheckedRunnable<Exception> assertTask(final int numberOfPrimaryShards, final Map<ShardId, Long> numDocsPerShard) {
         return () -> {
             final ClusterState clusterState = client().admin().cluster().prepareState().get().getState();