Check before switching to strict mode

Signed-off-by: Lakshya Taragi <lakshya.taragi@gmail.com>

Author: ltaragi

server/src/internalClusterTest/java/org/opensearch/remotemigration/RemoteStoreMigrationSettingsUpdateIT.java

@@ -11,9 +11,11 @@
 import org.opensearch.action.admin.cluster.snapshots.restore.RestoreSnapshotResponse;
 import org.opensearch.client.Client;
 import org.opensearch.common.settings.Settings;
+import org.opensearch.common.settings.SettingsException;
 import org.opensearch.core.rest.RestStatus;
 import org.opensearch.index.IndexSettings;
 import org.opensearch.indices.replication.common.ReplicationType;
+import org.opensearch.test.InternalTestCluster;
 import org.opensearch.test.OpenSearchIntegTestCase;
 
 import java.util.Optional;
@@ -76,6 +78,37 @@ public void testNewIndexIsRemoteStoreBackedForRemoteStoreDirectionAndMixedMode()
         assertRemoteStoreBackedIndex(indexName2);
     }
 
+    // compatibility mode setting test
+
+    public void testSwitchToStrictMode() throws Exception {
+        logger.info(" --> initialize cluster");
+        initializeCluster(false);
+
+        logger.info(" --> create a mixed mode cluster");
+        setClusterMode(MIXED.mode);
+        addRemote = true;
+        String remoteNodeName = internalCluster().startNode();
+        addRemote = false;
+        String nonRemoteNodeName = internalCluster().startNode();
+        internalCluster().validateClusterFormed();
+        assertNodeInCluster(remoteNodeName);
+        assertNodeInCluster(nonRemoteNodeName);
+
+        logger.info(" --> attempt switching to strict mode");
+        SettingsException exception = assertThrows(SettingsException.class, () -> setClusterMode(STRICT.mode));
+        assertEquals(
+            "can not switch to STRICT compatibility mode when the cluster contains both remote and non-remote nodes",
+            exception.getMessage()
+        );
+
+        logger.info(" --> stop remote node");
+        internalCluster().stopRandomNode(InternalTestCluster.nameFilter(remoteNodeName));
+        ensureStableCluster(2);
+
+        logger.info(" --> attempt switching to strict mode");
+        setClusterMode(STRICT.mode);
+    }
+
     // verify that the created index is not remote store backed
     private void assertNonRemoteStoreBackedIndex(String indexName) {
         Settings indexSettings = client.admin().indices().prepareGetIndex().execute().actionGet().getSettings().get(indexName);

server/src/main/java/org/opensearch/action/admin/cluster/settings/TransportClusterUpdateSettingsAction.java

@@ -53,12 +53,17 @@
 import org.opensearch.common.Priority;
 import org.opensearch.common.inject.Inject;
 import org.opensearch.common.settings.ClusterSettings;
+import org.opensearch.common.settings.SettingsException;
 import org.opensearch.core.action.ActionListener;
 import org.opensearch.core.common.io.stream.StreamInput;
+import org.opensearch.node.remotestore.RemoteStoreNodeService;
 import org.opensearch.threadpool.ThreadPool;
 import org.opensearch.transport.TransportService;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
 
 /**
  * Transport action for updating cluster settings
@@ -137,6 +142,7 @@ protected void clusterManagerOperation(
         final ClusterState state,
         final ActionListener<ClusterUpdateSettingsResponse> listener
     ) {
+        validateCompatibilityModeSettingRequest(request, state);
         final SettingsUpdater updater = new SettingsUpdater(clusterSettings);
         clusterService.submitStateUpdateTask(
             "cluster_update_settings",
@@ -264,4 +270,27 @@ public ClusterState execute(final ClusterState currentState) {
         );
     }
 
+    /**
+     * Verifies that while trying to switch to STRICT compatibility mode, all nodes must be of the
+     * same type (all remote or all non-remote). If not, it throws SettingsException error
+     * @param request cluster settings update request, for settings to be updated and new values
+     * @param clusterState current state of cluster, for information on nodes
+     */
+    private void validateCompatibilityModeSettingRequest(ClusterUpdateSettingsRequest request, ClusterState clusterState) {
+        if (RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING.exists(request.persistentSettings())) {
+            String value = request.persistentSettings().get(RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING.getKey());
+            if (value.equals(RemoteStoreNodeService.CompatibilityMode.STRICT.mode)) {
+                List<DiscoveryNode> discoveryNodeList = new ArrayList<>(clusterState.nodes().getNodes().values());
+                Optional<DiscoveryNode> remoteNode = discoveryNodeList.stream().filter(DiscoveryNode::isRemoteStoreNode).findFirst();
+                Optional<DiscoveryNode> nonRemoteNode = discoveryNodeList.stream()
+                    .filter(dn -> dn.isRemoteStoreNode() == false)
+                    .findFirst();
+                if (remoteNode.isPresent() && nonRemoteNode.isPresent()) {
+                    throw new SettingsException(
+                        "can not switch to STRICT compatibility mode when the cluster contains both remote and non-remote nodes"
+                    );
+                }
+            }
+        }
+    }
 }