Dangling indices strip aliases

server/src/main/java/org/elasticsearch/gateway/DanglingIndicesState.java

@@ -143,7 +143,7 @@ Map<Index, IndexMetaData> findNewDanglingIndices(final MetaData metaData) {
                 } else {
                     logger.info("[{}] dangling index exists on local file system, but not in cluster metadata, " +
                                 "auto import to cluster state", indexMetaData.getIndex());
-                    newIndices.put(indexMetaData.getIndex(), indexMetaData);
+                    newIndices.put(indexMetaData.getIndex(), stripAliases(indexMetaData));
                 }
             }
             return newIndices;
@@ -153,6 +153,20 @@ Map<Index, IndexMetaData> findNewDanglingIndices(final MetaData metaData) {
         }
     }
 
+    /**
+     * Dangling importing indices with aliases is dangerous, it could for instance result in inability to write to an existing alias if it
+     * previously had only one index with any is_write_index indication.
+     */
+    private IndexMetaData stripAliases(IndexMetaData indexMetaData) {
+        if (indexMetaData.getAliases().isEmpty()) {
+            return indexMetaData;
+        } else {
+            logger.info("[{}] stripping aliases: {} from index before importing",
+                indexMetaData.getIndex(), indexMetaData.getAliases().keys());
+            return IndexMetaData.builder(indexMetaData).removeAllAliases().build();
+        }
+    }
+
     /**
      * Allocates the provided list of the dangled indices by sending them to the master node
      * for allocation.

server/src/test/java/org/elasticsearch/gateway/DanglingIndicesStateTests.java

@@ -19,6 +19,7 @@
 package org.elasticsearch.gateway;
 
 import org.elasticsearch.Version;
+import org.elasticsearch.cluster.metadata.AliasMetaData;
 import org.elasticsearch.cluster.metadata.IndexGraveyard;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
@@ -158,6 +159,28 @@ public void testDanglingIndicesNotImportedWhenTombstonePresent() throws Exceptio
         }
     }
 
+    public void testDanglingIndicesStripAliases() throws Exception {
+        try (NodeEnvironment env = newNodeEnvironment()) {
+            MetaStateService metaStateService = new MetaStateService(env, xContentRegistry());
+            DanglingIndicesState danglingState = createDanglingIndicesState(env, metaStateService);
+
+            final Settings.Builder settings = Settings.builder().put(indexSettings).put(IndexMetaData.SETTING_INDEX_UUID, "test1UUID");
+            IndexMetaData dangledIndex = IndexMetaData.builder("test1")
+                .settings(settings)
+                .putAlias(AliasMetaData.newAliasMetaDataBuilder("test_aliasd").build())
+                .build();
+            metaStateService.writeIndex("test_write", dangledIndex);
+            assertThat(dangledIndex.getAliases().size(), equalTo(1));
+
+            final MetaData metaData = MetaData.builder().build();
+            Map<Index, IndexMetaData> newDanglingIndices = danglingState.findNewDanglingIndices(metaData);
+            assertThat(newDanglingIndices.size(), equalTo(1));
+            Map.Entry<Index, IndexMetaData> entry = newDanglingIndices.entrySet().iterator().next();
+            assertThat(entry.getKey().getName(), equalTo("test1"));
+            assertThat(entry.getValue().getAliases().size(), equalTo(0));
+        }
+    }
+
     private DanglingIndicesState createDanglingIndicesState(NodeEnvironment env, MetaStateService metaStateService) {
         return new DanglingIndicesState(env, metaStateService, null, mock(ClusterService.class));
     }