Add Recommission service layer changes logic.

server/src/main/java/org/opensearch/cluster/decommission/DecommissionService.java

@@ -16,6 +16,7 @@
 import org.opensearch.cluster.ClusterState;
 import org.opensearch.cluster.ClusterStateUpdateTask;
 import org.opensearch.cluster.NotClusterManagerException;
+import org.opensearch.cluster.ack.ClusterStateUpdateResponse;
 import org.opensearch.cluster.coordination.CoordinationMetadata;
 import org.opensearch.cluster.metadata.DecommissionAttributeMetadata;
 import org.opensearch.cluster.coordination.ClusterBootstrapService;
@@ -415,6 +416,40 @@ private static void ensureNoAwarenessAttributeDecommissioned(
         }
     }
 
+    public void clearDecommissionStatus(final ActionListener<ClusterStateUpdateResponse> listener) {
+        // Execute cluster update to remove decommission attribute from cluster state metadata.
+        clusterService.submitStateUpdateTask(
+                "delete_decommission",
+                new ClusterStateUpdateTask(Priority.URGENT) {
+                    @Override
+                    public ClusterState execute(ClusterState currentState) {
+                        return deleteDecommissionAttribute(currentState);
+                    }
+
+                    @Override
+                    public void onFailure(String source, Exception e) {
+                        logger.error(() -> new ParameterizedMessage("Failed to clear decommission attribute."), e);
+                        listener.onFailure(e);
+                    }
+
+                    @Override
+                    public void clusterStateProcessed(String source, ClusterState oldState, ClusterState newState) {
+                        // Once the cluster state is processed we can try to recommission nodes by setting the weights for the zone.
+                        // TODO Set the weights for the recommissioning zone.
+                        listener.onResponse(new ClusterStateUpdateResponse(true));
+                    }
+                }
+        );
+    }
+
+    ClusterState deleteDecommissionAttribute(final ClusterState currentState) {
+        logger.info("Delete decommission request received");
+        Metadata metadata = currentState.metadata();
+        Metadata.Builder mdBuilder = Metadata.builder(metadata);
+        mdBuilder.removeCustom(DecommissionAttributeMetadata.TYPE);
+        return ClusterState.builder(currentState).metadata(mdBuilder).build();
+    }
+
     private static void ensureNoQuorumLossDueToDecommissioning(
         DecommissionAttribute decommissionAttribute,
         Set<DiscoveryNode> clusterManagerNodesToBeDecommissioned,

server/src/test/java/org/opensearch/cluster/decommission/DecommissionServiceTests.java

@@ -199,6 +199,23 @@ public void testDecommissioningNotInitiatedWhenNotEnoughClusterManagerNodes() {
         assertThat(e.getMessage(), Matchers.endsWith("cannot proceed with decommission request. Cluster might go into quorum loss"));
     }
 
+    public void testClearDecommissionAttribute() {
+        final ClusterSettings settings = new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
+        DecommissionAttribute decommissionAttribute = new DecommissionAttribute("zone", "zone-2");
+        org.opensearch.cluster.metadata.DecommissionAttributeMetadata decommissionAttributeMetadata =
+                new org.opensearch.cluster.metadata.DecommissionAttributeMetadata(decommissionAttribute, DecommissionStatus.DECOMMISSION_SUCCESSFUL);
+        ClusterState clusterState = ClusterState.builder(new ClusterName("test"))
+                .metadata(Metadata.builder()
+                        .putCustom(org.opensearch.cluster.metadata.DecommissionAttributeMetadata.TYPE, decommissionAttributeMetadata).build())
+                .build();
+
+        final ClusterState newClusterState = this.decommissionService.deleteDecommissionAttribute(clusterState);
+        org.opensearch.cluster.metadata.DecommissionAttributeMetadata metadata = newClusterState.metadata().custom(org.opensearch.cluster.metadata.DecommissionAttributeMetadata.TYPE);
+
+        // Decommission Attribute should be removed.
+        assertNull(metadata);
+    }
+
     private ClusterState addDataNodes(ClusterState clusterState, String zone, String... nodeIds) {
         DiscoveryNodes.Builder nodeBuilder = DiscoveryNodes.builder(clusterState.nodes());
         org.opensearch.common.collect.List.of(nodeIds).forEach(nodeId -> nodeBuilder.add(newDataNode(nodeId, singletonMap("zone", zone))));