Deprecate node local storage setting (#54374)

This setting is not documented and has dubious value since it means
there can be nodes in the cluster (non-data and non-master nodes) that
do not have persistent node IDs. This does not have any use cases so
this commit removes the setting.

Author: jasontedor

docs/reference/migration/index.asciidoc

@@ -11,6 +11,7 @@ For information about how to upgrade your cluster, see <<setup-upgrade>>.
 
 --
 
+include::migrate_7_8.asciidoc[]
 include::migrate_7_7.asciidoc[]
 include::migrate_7_6.asciidoc[]
 include::migrate_7_5.asciidoc[]

docs/reference/migration/migrate_7_8.asciidoc

@@ -0,0 +1,30 @@
+[[breaking-changes-7.8]]
+== Breaking changes in 7.8
+++++
+<titleabbrev>7.8</titleabbrev>
+++++
+
+This section discusses the changes that you need to be aware of when migrating
+your application to Elasticsearch 7.8.
+
+See also <<release-highlights>> and <<es-release-notes>>.
+
+coming[7.8.0]
+
+//NOTE: The notable-breaking-changes tagged regions are re-used in the
+//Installation and Upgrade Guide
+
+//tag::notable-breaking-changes[]
+
+//end::notable-breaking-changes[]
+
+[discrete]
+[[breaking_78_settings_changes]]
+=== Settings changes
+
+[discrete]
+[[deprecate-node-local-storage]]
+==== `node.local_storage` is deprecated
+
+In Elasticsearch 7.8.0, the setting `node.local_storage` was deprecated and
+beginning in Elasticsearch 8.0.0 all nodes will require local storage.

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

@@ -214,7 +214,8 @@ public class Node implements Closeable {
     * and {@link #NODE_MASTER_SETTING} must also be false.
     *
     */
-    public static final Setting<Boolean> NODE_LOCAL_STORAGE_SETTING = Setting.boolSetting("node.local_storage", true, Property.NodeScope);
+    public static final Setting<Boolean> NODE_LOCAL_STORAGE_SETTING =
+        Setting.boolSetting("node.local_storage", true, Property.Deprecated, Property.NodeScope);
     public static final Setting<String> NODE_NAME_SETTING = Setting.simpleString("node.name", Property.NodeScope);
     public static final Setting.AffixSetting<String> NODE_ATTRIBUTES = Setting.prefixKeySetting("node.attr.", (key) ->
         new Setting<>(key, "", (value) -> {

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

@@ -22,6 +22,7 @@
 import org.apache.lucene.util.LuceneTestCase;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.io.PathUtils;
+import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.common.util.set.Sets;
@@ -438,6 +439,7 @@ public void testNodeIdNotPersistedAtInitialization() throws IOException {
         env = newNodeEnvironment(Settings.EMPTY);
         assertThat(env.nodeId(), not(equalTo(nodeID)));
         env.close();
+        assertSettingDeprecationsAndWarnings(new Setting<?>[]{Node.NODE_LOCAL_STORAGE_SETTING});
     }
 
     public void testExistingTempFiles() throws IOException {