Deprecate max_local_storage_nodes (#42426)

Allows this setting to be removed in 8.0, see #42428

Author: ywelsch

docs/reference/modules/node.asciidoc

@@ -282,8 +282,8 @@ your data! The RPM and Debian distributions do this for you already.
 === `node.max_local_storage_nodes`
 
 The <<data-path,data path>> can be shared by multiple nodes, even by nodes from different
-clusters. This is very useful for testing failover and different configurations on your development
-machine. In production, however, it is recommended to run only one node of Elasticsearch per server.
+clusters. It is recommended however to only run one node of Elasticsearch using the same data path.
+This setting is deprecated in 7.x and will be removed in version 8.0.
 
 By default, Elasticsearch is configured to prevent more than one node from sharing the same data
 path. To allow for more than one node (e.g., on your development machine), use the setting

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

@@ -164,7 +164,7 @@ public String toString() {
      * Maximum number of data nodes that should run in an environment.
      */
     public static final Setting<Integer> MAX_LOCAL_STORAGE_NODES_SETTING = Setting.intSetting("node.max_local_storage_nodes", 1, 1,
-        Property.NodeScope);
+        Property.NodeScope, Property.Deprecated);
 
     /**
      * Seed for determining a persisted unique uuid of this node. If the node has already a persisted uuid on disk,

server/src/test/java/org/elasticsearch/env/NodeEnvironmentTests.java

@@ -73,6 +73,8 @@ public void testNodeLockSillySettings() {
         int max = NodeEnvironment.MAX_LOCAL_STORAGE_NODES_SETTING.get(
                 Settings.builder().put(NodeEnvironment.MAX_LOCAL_STORAGE_NODES_SETTING.getKey(), value).build());
         assertEquals(value, max);
+        assertWarnings("[node.max_local_storage_nodes] setting was deprecated in Elasticsearch and will be removed in a future release! " +
+            "See the breaking changes documentation for the next major version.");
     }
 
     public void testNodeLockSingleEnvironment() throws IOException {
@@ -95,6 +97,8 @@ public void testNodeLockSingleEnvironment() throws IOException {
         }
         env.close();
         assertThat(env.lockedShards(), empty());
+        assertWarnings("[node.max_local_storage_nodes] setting was deprecated in Elasticsearch and will be removed in a future release! " +
+            "See the breaking changes documentation for the next major version.");
     }
 
     @SuppressForbidden(reason = "System.out.*")
@@ -129,6 +133,8 @@ public void testNodeLockMultipleEnvironment() throws IOException {
             assertEquals(first.nodeDataPaths()[i].getParent(), second.nodeDataPaths()[i].getParent());
         }
         IOUtils.close(first, second);
+        assertWarnings("[node.max_local_storage_nodes] setting was deprecated in Elasticsearch and will be removed in a future release! " +
+            "See the breaking changes documentation for the next major version.");
     }
 
     public void testShardLock() throws Exception {