add new role for Offline Nodes

server/src/main/java/org/opensearch/cluster/node/DiscoveryNode.java

@@ -128,6 +128,10 @@ public static boolean isSearchNode(Settings settings) {
         return hasRole(settings, DiscoveryNodeRole.SEARCH_ROLE);
     }
 
+    public static boolean isOfflineNode(Settings settings) {
+        return hasRole(settings, DiscoveryNodeRole.OFFLINE_ROLE);
+    }
+
     private final String nodeName;
     private final String nodeId;
     private final String ephemeralId;

server/src/main/java/org/opensearch/cluster/node/DiscoveryNodeRole.java

@@ -310,6 +310,18 @@ public Setting<Boolean> legacySetting() {
 
     };
 
+    /**
+     * Represents the role for a Offline node, which is dedicated only to run background tasks.
+     */
+    public static final DiscoveryNodeRole OFFLINE_ROLE = new DiscoveryNodeRole("offline", "o") {
+
+        @Override
+        public Setting<Boolean> legacySetting() {
+            // offline role is added in 2.15 so doesn't need to configure legacy setting
+            return null;
+        }
+    };
+
     /**
      * The built-in node roles.
      */

server/src/main/java/org/opensearch/env/NodeEnvironment.java

@@ -94,6 +94,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.Semaphore;
@@ -391,6 +392,20 @@
                 ensureNoFileCacheData(fileCacheNodePath);
             }
 
+            if (DiscoveryNode.isOfflineNode(settings) && DiscoveryNode.getRolesFromSettings(settings).size() > 1) {
+                final String message = String.format(
+                    Locale.ROOT,
+                    "Offline Nodes cannot be used with any other roles, only %s role should be provided. Please remove %s roles",
+                    DiscoveryNodeRole.OFFLINE_ROLE.roleName(),
+                    DiscoveryNode.getRolesFromSettings(settings)
+                        .stream()
+                        .map(DiscoveryNodeRole::roleName)
+                        .filter(role1 -> Objects.equals(role1, DiscoveryNodeRole.OFFLINE_ROLE.roleName()))
+                        .collect(Collectors.joining(","))
+                );
+                throw new IllegalStateException(message);
+            }
+
             this.nodeMetadata = loadNodeMetadata(settings, logger, nodePaths);
             this.indexStoreListener = indexStoreListener;
             success = true;