Pre conditions check before updating weighted routing metadata

CHANGELOG.md

@@ -109,6 +109,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Migrate client transports to Apache HttpClient / Core 5.x ([#4459](https://github.com/opensearch-project/OpenSearch/pull/4459))
 - Refactored BalancedAllocator.Balancer to LocalShardsBalancer ([#4761](https://github.com/opensearch-project/OpenSearch/pull/4761))
 - Fail weight update when decommission ongoing and fail decommission when attribute not weighed away ([#4839](https://github.com/opensearch-project/OpenSearch/pull/4839))
+- Allow weight updates for non decommissioned attribute([#4955](https://github.com/opensearch-project/OpenSearch/pull/4955))
 ### Deprecated
 ### Removed
 - Remove deprecated code to add node name into log pattern of log4j property file ([#4568](https://github.com/opensearch-project/OpenSearch/pull/4568))

server/src/main/java/org/opensearch/cluster/routing/WeightedRoutingService.java

@@ -34,6 +34,7 @@
 
 import java.util.List;
 import java.util.Locale;
+import java.util.Objects;
 
 import static org.opensearch.action.ValidateActions.addValidationError;
 
@@ -70,8 +71,8 @@ public void registerWeightedRoutingMetadata(
         clusterService.submitStateUpdateTask("update_weighted_routing", new ClusterStateUpdateTask(Priority.URGENT) {
             @Override
             public ClusterState execute(ClusterState currentState) {
-                // verify currently no decommission action is ongoing
-                ensureNoOngoingDecommissionAction(currentState);
+                // verify weights will not be updated for a decommissioned attribute
+                ensureNoWeightUpdateForDecommissionedAttribute(currentState, request);
                 Metadata metadata = currentState.metadata();
                 Metadata.Builder mdBuilder = Metadata.builder(currentState.metadata());
                 WeightedRoutingMetadata weightedRoutingMetadata = metadata.custom(WeightedRoutingMetadata.TYPE);
@@ -159,9 +160,18 @@ public void verifyAwarenessAttribute(String attributeName) {
         }
     }
 
-    public void ensureNoOngoingDecommissionAction(ClusterState state) {
+    public void ensureNoWeightUpdateForDecommissionedAttribute(ClusterState state, ClusterPutWeightedRoutingRequest request) {
         DecommissionAttributeMetadata decommissionAttributeMetadata = state.metadata().decommissionAttributeMetadata();
-        if (decommissionAttributeMetadata != null && decommissionAttributeMetadata.status().equals(DecommissionStatus.FAILED) == false) {
+        if (decommissionAttributeMetadata != null
+            && decommissionAttributeMetadata.status().equals(DecommissionStatus.FAILED) == false
+            && Objects.equals(
+                request.getWeightedRouting().attributeName(),
+                decommissionAttributeMetadata.decommissionAttribute().attributeName()
+            )
+            && Objects.equals(
+                request.getWeightedRouting().weights().get(decommissionAttributeMetadata.decommissionAttribute().attributeValue()),
+                0.0
+            ) == false) {
             throw new IllegalStateException(
                 "a decommission action is ongoing with status ["
                     + decommissionAttributeMetadata.status().status()

server/src/test/java/org/opensearch/cluster/routing/WeightedRoutingServiceTests.java

@@ -362,4 +362,36 @@ public void onFailure(Exception e) {}
         weightedRoutingService.registerWeightedRoutingMetadata(request.request(), listener);
         assertTrue(countDownLatch.await(30, TimeUnit.SECONDS));
     }
+
+    public void testAddWeightedRoutingPassesWhenWeightOfDecommissionedAttributeStillZero() throws InterruptedException {
+        Map<String, Double> weights = Map.of("zone_A", 0.0, "zone_B", 1.0, "zone_C", 1.0);
+        DecommissionStatus status = DecommissionStatus.SUCCESSFUL;
+        ClusterState state = clusterService.state();
+        state = setWeightedRoutingWeights(state, weights);
+        state = setDecommissionAttribute(state, status);
+        ClusterState.Builder builder = ClusterState.builder(state);
+        ClusterServiceUtils.setState(clusterService, builder);
+
+        ClusterPutWeightedRoutingRequestBuilder request = new ClusterPutWeightedRoutingRequestBuilder(
+            client,
+            ClusterAddWeightedRoutingAction.INSTANCE
+        );
+        Map<String, Double> updatedWeights = Map.of("zone_A", 0.0, "zone_B", 2.0, "zone_C", 1.0);
+        WeightedRouting updatedWeightedRouting = new WeightedRouting("zone", updatedWeights);
+        request.setWeightedRouting(updatedWeightedRouting);
+        final CountDownLatch countDownLatch = new CountDownLatch(1);
+        ActionListener<ClusterStateUpdateResponse> listener = new ActionListener<ClusterStateUpdateResponse>() {
+            @Override
+            public void onResponse(ClusterStateUpdateResponse clusterStateUpdateResponse) {
+                assertTrue(clusterStateUpdateResponse.isAcknowledged());
+                countDownLatch.countDown();
+            }
+
+            @Override
+            public void onFailure(Exception e) {}
+        };
+        weightedRoutingService.registerWeightedRoutingMetadata(request.request(), listener);
+        assertTrue(countDownLatch.await(30, TimeUnit.SECONDS));
+        assertEquals(updatedWeightedRouting, clusterService.state().metadata().weightedRoutingMetadata().getWeightedRouting());
+    }
 }