[Backport 2.x] Pass localNode info to all plugins on node start (#8192)

* [Enhancement] Pass localNode info to all plugins on node start (#7919)

* Updates Node start to now pass localNode info so that it is available directly to a plugin instead of hacky implementation

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Adds this PR to changelog

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Makes onNodeStarted call plugin agnostic

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Marking onNodeStarted() as deprecated

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Adds a test to verify the behaviour of new signature of onNodeStarted

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Updates test to also check for nodeId

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

* Adds instructions to use the overloaded implementation of onNodeStarted and adds a test to check that current plugins are not affect with this implementation

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

---------

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>
Signed-off-by: Darshit Chanpura <35282393+DarshitChanpura@users.noreply.github.com>
(cherry picked from commit 40d7583)

* Adds a CHANGELOG entry

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

---------

Signed-off-by: Darshit Chanpura <dchanp@amazon.com>

CHANGELOG.md

@@ -52,6 +52,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Rename QueryPhase actors like Suggest, Rescore to be processors rather than phase ([#8025](https://github.com/opensearch-project/OpenSearch/pull/8025))
 - [Snapshot Interop] Add Changes in Create Snapshot Flow for remote store interoperability. ([#8071](https://github.com/opensearch-project/OpenSearch/pull/8071))
 - Allow insecure string settings to warn-log usage and advise to migration of a newer secure variant ([#5496](https://github.com/opensearch-project/OpenSearch/pull/5496))
+- Pass localNode info to all plugins on node start ([#7919](https://github.com/opensearch-project/OpenSearch/pull/7919)
 
 ### Deprecated
 

server/src/main/java/org/opensearch/node/Node.java

@@ -1358,7 +1358,7 @@ public void onTimeout(TimeValue timeout) {
 
         logger.info("started");
 
-        pluginsService.filterPlugins(ClusterPlugin.class).forEach(ClusterPlugin::onNodeStarted);
+        pluginsService.filterPlugins(ClusterPlugin.class).forEach(plugin -> plugin.onNodeStarted(clusterService.localNode()));
 
         return this;
     }

server/src/main/java/org/opensearch/plugins/ClusterPlugin.java

@@ -32,6 +32,7 @@
 
 package org.opensearch.plugins;
 
+import org.opensearch.cluster.node.DiscoveryNode;
 import org.opensearch.cluster.routing.allocation.ExistingShardsAllocator;
 import org.opensearch.cluster.routing.allocation.allocator.ShardsAllocator;
 import org.opensearch.cluster.routing.allocation.decider.AllocationDecider;
@@ -86,7 +87,19 @@ default Map<String, ExistingShardsAllocator> getExistingShardsAllocators() {
 
     /**
      * Called when the node is started
+     *
+     * DEPRECATED: Use {@link #onNodeStarted(DiscoveryNode)} for newer implementations.
      */
+    @Deprecated
     default void onNodeStarted() {}
 
+    /**
+     * Called when node is started. DiscoveryNode argument is passed to allow referring localNode value inside plugin
+     *
+     * @param localNode local Node info
+     */
+    default void onNodeStarted(DiscoveryNode localNode) {
+        onNodeStarted();
+    }
+
 }

server/src/test/java/org/opensearch/plugins/ClusterPluginTests.java

@@ -0,0 +1,78 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugins;
+
+import org.opensearch.cluster.node.DiscoveryNode;
+import org.opensearch.test.OpenSearchSingleNodeTestCase;
+
+import java.util.Collection;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+public class ClusterPluginTests extends OpenSearchSingleNodeTestCase {
+
+    @Override
+    protected Collection<Class<? extends Plugin>> getPlugins() {
+        return pluginList(DummyClusterPlugin.class, DummyClusterPlugin2.class);
+    }
+
+    public void testOnNodeStarted_shouldContainLocalNodeInfo() {
+
+        DiscoveryNode localNode = DummyClusterPlugin.getLocalNode();
+
+        assertTrue(localNode != null);
+        // TODO Figure out if there is a way to check ephemeralId
+        assertTrue(localNode.getId().equals(node().getNodeEnvironment().nodeId()));
+    }
+
+    public void testOnNodeStarted_shouldCallDeprecatedMethod() {
+        DummyClusterPlugin2 dummyClusterPlugin2 = mock(DummyClusterPlugin2.class);
+        dummyClusterPlugin2.onNodeStarted();
+        verify(dummyClusterPlugin2, times(1)).onNodeStarted();
+
+        DiscoveryNode localNode = DummyClusterPlugin2.getLocalNode();
+        assertTrue(localNode != null);
+    }
+
+}
+
+final class DummyClusterPlugin extends Plugin implements ClusterPlugin {
+
+    private static volatile DiscoveryNode localNode;
+
+    public DummyClusterPlugin() {}
+
+    @Override
+    public void onNodeStarted(DiscoveryNode localNode) {
+        DummyClusterPlugin.localNode = localNode;
+    }
+
+    public static DiscoveryNode getLocalNode() {
+        return localNode;
+    }
+}
+
+class DummyClusterPlugin2 extends Plugin implements ClusterPlugin {
+
+    private static volatile DiscoveryNode localNode;
+
+    public DummyClusterPlugin2() {}
+
+    @Override
+    public void onNodeStarted() {
+        localNode = mock(DiscoveryNode.class);
+    }
+
+    public static DiscoveryNode getLocalNode() {
+        return localNode;
+    }
+
+}