Fix weighted routing metadata deserialization error during node restart

CHANGELOG.md

@@ -83,6 +83,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Update to Apache Lucene 9.4.0 ([#4661](https://github.com/opensearch-project/OpenSearch/pull/4661))
 - Controlling discovery for decommissioned nodes ([#4590](https://github.com/opensearch-project/OpenSearch/pull/4590))
 - Backport Apache Lucene version change for 2.4.0 ([#4677](https://github.com/opensearch-project/OpenSearch/pull/4677))
+- Fix weighted routing metadata deserialization error on process restart ([#4691](https://github.com/opensearch-project/OpenSearch/pull/4691))
 - Refactor Base Action class javadocs to OpenSearch.API ([#4732](https://github.com/opensearch-project/OpenSearch/pull/4732))
 - Migrate client transports to Apache HttpClient / Core 5.x ([#4459](https://github.com/opensearch-project/OpenSearch/pull/4459))
 

server/src/internalClusterTest/java/org/opensearch/cluster/routing/WeightedRoutingIT.java

@@ -242,4 +242,46 @@ public void testGetWeightedRouting_WeightsAreSet() throws IOException {
         assertEquals(weightedRouting, weightedRoutingResponse.weights());
         assertEquals("3.0", weightedRoutingResponse.getLocalNodeWeight());
     }
+
+    public void testWeightedRoutingMetadataOnOSProcessRestart() throws Exception {
+        Settings commonSettings = Settings.builder()
+            .put("cluster.routing.allocation.awareness.attributes", "zone")
+            .put("cluster.routing.allocation.awareness.force.zone.values", "a,b,c")
+            .build();
+
+        internalCluster().startNodes(
+            Settings.builder().put(commonSettings).put("node.attr.zone", "a").build(),
+            Settings.builder().put(commonSettings).put("node.attr.zone", "b").build(),
+            Settings.builder().put(commonSettings).put("node.attr.zone", "c").build()
+        );
+
+        logger.info("--> waiting for nodes to form a cluster");
+        ClusterHealthResponse health = client().admin().cluster().prepareHealth().setWaitForNodes("3").execute().actionGet();
+        assertThat(health.isTimedOut(), equalTo(false));
+
+        ensureGreen();
+
+        logger.info("--> setting shard routing weights for weighted round robin");
+        Map<String, Double> weights = Map.of("a", 1.0, "b", 2.0, "c", 3.0);
+        WeightedRouting weightedRouting = new WeightedRouting("zone", weights);
+        // put api call to set weights
+        ClusterPutWeightedRoutingResponse response = client().admin()
+            .cluster()
+            .prepareWeightedRouting()
+            .setWeightedRouting(weightedRouting)
+            .get();
+        assertEquals(response.isAcknowledged(), true);
+
+        ensureStableCluster(3);
+
+        // routing weights are set in cluster metadata
+        assertNotNull(internalCluster().clusterService().state().metadata().weightedRoutingMetadata());
+
+        ensureGreen();
+
+        // Restart a random data node and check that OS process comes healthy
+        internalCluster().restartRandomDataNode();
+        ensureGreen();
+        assertNotNull(internalCluster().clusterService().state().metadata().weightedRoutingMetadata());
+    }
 }

server/src/main/java/org/opensearch/cluster/metadata/WeightedRoutingMetadata.java

@@ -90,8 +90,6 @@ public static WeightedRoutingMetadata fromXContent(XContentParser parser) throws
         Map<String, Double> weights = new HashMap<>();
         WeightedRouting weightedRouting = null;
         XContentParser.Token token;
-        // move to the first alias
-        parser.nextToken();
         String awarenessField = null;
 
         while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {