NIFI-16165 - Expose Node Connection State through NodeTypeProvider

src/main/java/org/apache/nifi/controller/NodeConnectionState.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.nifi.controller;
+
+public enum NodeConnectionState {
+    /**
+     * A node has issued a connection request to the cluster, but has not yet
+     * sent a heartbeat. A connecting node can transition to DISCONNECTED or CONNECTED. The cluster
+     * will not accept any external requests to change the flow while any node is in
+     * this state.
+     */
+    CONNECTING,
+
+    /**
+     * A node that is connected to the cluster. A connecting node transitions
+     * to connected after the cluster receives the node's first heartbeat. A
+     * connected node can transition to disconnecting.
+     */
+    CONNECTED,
+
+    /**
+     * A node that is in the process of offloading its FlowFiles from the node.
+     */
+    OFFLOADING,
+
+    /**
+     * A node that is in the process of disconnecting from the cluster.
+     * A DISCONNECTING node will always transition to DISCONNECTED.
+     */
+    DISCONNECTING,
+
+    /**
+     * A node that has offloaded its FlowFiles from the node.
+     */
+    OFFLOADED,
+
+    /**
+     * A node that is not connected to the cluster.
+     * A DISCONNECTED node can transition to CONNECTING.
+     */
+    DISCONNECTED,
+
+    /**
+     * A NodeConnectionState of REMOVED indicates that the node was removed from the cluster
+     * and is used in order to notify other nodes in the cluster.
+     */
+    REMOVED,
+
+    /**
+     * A NiFi instance that is not configured to participate in a cluster.
+     */
+    STANDALONE
+}

src/main/java/org/apache/nifi/controller/NodeTypeProvider.java

@@ -47,6 +47,17 @@ default boolean isConnected() {
         return false;
     }
 
+    /**
+     * Returns the current node connection state and never null. The compatibility default is
+     * {@link NodeConnectionState#STANDALONE}. Providers for clustered NiFi should override this
+     * method with the current node lifecycle state.
+     *
+     * @return current node connection state
+     */
+    default NodeConnectionState getNodeConnectionState() {
+        return NodeConnectionState.STANDALONE;
+    }
+
     /**
      * @return true if this instance is the primary node in the cluster; false otherwise
      */

src/test/java/org/apache/nifi/controller/NodeTypeProviderTest.java

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.nifi.controller;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class NodeTypeProviderTest {
+
+    @Test
+    void getNodeConnectionStateReturnsStandaloneForLegacyImplementations() {
+        final NodeTypeProvider nodeTypeProvider = new NodeTypeProvider() {
+            @Override
+            public boolean isClustered() {
+                return false;
+            }
+
+            @Override
+            public boolean isPrimary() {
+                return false;
+            }
+        };
+
+        assertEquals(NodeConnectionState.STANDALONE, nodeTypeProvider.getNodeConnectionState());
+    }
+}