[Rest Api Compatibility] Dummy REST action for indices.upgrade api (#75136)

indices upgrade api (/_upgrade or /{index}/_upgrade) was removed and _reindex is suggested to be used instead.
There is no easy way to translate _upgrade request to _reindex requests. The dummy Upgrade action will return an exception to a user with a message indicating that _reindex should be used.

upgrade api removal #64732
relates #51816

Author: pgomulka

rest-api-spec/build.gradle

@@ -68,7 +68,10 @@ def v7compatibilityNotSupportedTests = {
           // translog settings removal is not supported under compatible api
           'indices.stats/20_translog/Translog retention settings are deprecated',
           'indices.stats/20_translog/Translog retention without soft_deletes',
-          'indices.stats/20_translog/Translog stats on closed indices without soft-deletes'
+          'indices.stats/20_translog/Translog stats on closed indices without soft-deletes',
+
+          // upgrade api will only get a dummy endpoint returning an exception suggesting to use _reindex
+          'indices.upgrade/*/*'
   ]
 }
 tasks.named("yamlRestCompatTest").configure {
@@ -90,11 +93,6 @@ tasks.named("yamlRestCompatTest").configure {
     'indices.put_template/11_basic_with_types/Put template with empty mappings',
     'indices.shrink/30_copy_settings/Copy settings during shrink index',
     'indices.split/30_copy_settings/Copy settings during split index',
-    'indices.upgrade/10_basic/Basic test for upgrade indices',
-    'indices.upgrade/10_basic/Upgrade indices allow no indices',
-    'indices.upgrade/10_basic/Upgrade indices disallow no indices',
-    'indices.upgrade/10_basic/Upgrade indices disallow unavailable',
-    'indices.upgrade/10_basic/Upgrade indices ignore unavailable',
     'mlt/20_docs/Basic mlt query with docs',
     'mlt/30_unlike/Basic mlt query with unlike',
     'search.aggregation/200_top_hits_metric/top_hits aggregation with sequence numbers',

rest-api-spec/src/yamlRestCompatTest/resources/rest-api-spec/test/v7compat/indices.deprecated.upgrade/10_basic_upgrade.yml

@@ -0,0 +1,44 @@
+---
+setup:
+  - skip:
+      version: "9.0.0 - "
+      reason: "compatible from 8.x to 7.x"
+      features:
+        - "headers"
+        - "allowed_warnings_regex"
+
+---
+Basic test for upgrade indices:
+  - skip:
+      version: " - 7.10.99"
+      reason: "_upgrade api is deprecated since 7.11.0"
+      features:
+        - "warnings"
+  - do:
+      indices.create:
+        index: "test_index"
+        body:
+          settings:
+            index:
+              number_of_replicas: 0
+      headers:
+        Content-Type: "application/vnd.elasticsearch+json;compatible-with=7"
+        Accept: "application/vnd.elasticsearch+json;compatible-with=7"
+      allowed_warnings_regex:
+        - "\\[types removal\\].*"
+  - do:
+      catch: "bad_request"
+      indices.upgrade:
+        index: "test_index"
+      warnings:
+        - "The _upgrade API is no longer useful and will be removed. Instead, see _reindex\
+      \ API."
+      headers:
+        Content-Type: "application/vnd.elasticsearch+json;compatible-with=7"
+        Accept: "application/vnd.elasticsearch+json;compatible-with=7"
+      allowed_warnings_regex:
+        - "\\[types removal\\].*"
+  - match:
+      status: 400
+  - match:
+      error.reason: "/Upgrade.action.(GET|POST).(_upgrade|/test_index/_upgrade).was.removed,.use._reindex.API.instead/"

server/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -339,6 +339,7 @@
 import org.elasticsearch.rest.action.admin.indices.RestSimulateTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestSyncedFlushAction;
 import org.elasticsearch.rest.action.admin.indices.RestUpdateSettingsAction;
+import org.elasticsearch.rest.action.admin.indices.RestUpgradeActionDeprecated;
 import org.elasticsearch.rest.action.admin.indices.RestValidateQueryAction;
 import org.elasticsearch.rest.action.cat.AbstractCatAction;
 import org.elasticsearch.rest.action.cat.RestAliasAction;
@@ -796,6 +797,8 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         registerHandler.accept(new RestTemplatesAction());
         registerHandler.accept(new RestAnalyzeIndexDiskUsageAction());
 
+        registerHandler.accept(new RestUpgradeActionDeprecated());
+
         for (ActionPlugin plugin : actionPlugins) {
             for (RestHandler handler : plugin.getRestHandlers(settings, restController, clusterSettings, indexScopedSettings,
                     settingsFilter, indexNameExpressionResolver, nodesInCluster)) {

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestUpgradeActionDeprecated.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.rest.action.admin.indices;
+
+import org.elasticsearch.client.node.NodeClient;
+import org.elasticsearch.core.RestApiVersion;
+import org.elasticsearch.rest.BaseRestHandler;
+import org.elasticsearch.rest.BytesRestResponse;
+import org.elasticsearch.rest.RestRequest;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Locale;
+
+import static org.elasticsearch.rest.RestRequest.Method.GET;
+import static org.elasticsearch.rest.RestRequest.Method.POST;
+
+public class RestUpgradeActionDeprecated extends BaseRestHandler {
+    public static final String UPGRADE_API_DEPRECATION_MESSAGE =
+        "The _upgrade API is no longer useful and will be removed. Instead, see _reindex API.";
+
+    @Override
+    public List<Route> routes() {
+        return List.of(
+            Route.builder(POST, "/_upgrade")
+                .deprecated(UPGRADE_API_DEPRECATION_MESSAGE, RestApiVersion.V_7)
+                .build(),
+            Route.builder(POST, "/{index}/_upgrade")
+                .deprecated(UPGRADE_API_DEPRECATION_MESSAGE, RestApiVersion.V_7)
+                .build(),
+            Route.builder(GET, "/_upgrade")
+                .deprecated(UPGRADE_API_DEPRECATION_MESSAGE, RestApiVersion.V_7)
+                .build(),
+            Route.builder(GET, "/{index}/_upgrade")
+                .deprecated(UPGRADE_API_DEPRECATION_MESSAGE, RestApiVersion.V_7)
+                .build());
+    }
+
+    @Override
+    public String getName() {
+        return "upgrade_action";
+    }
+
+    @Override
+    public RestChannelConsumer prepareRequest(RestRequest request, NodeClient client) throws IOException {
+        request.param("index");
+        final UpgradeActionDeprecatedException exception = new UpgradeActionDeprecatedException(request);
+        return channel -> channel.sendResponse(new BytesRestResponse(channel, exception));
+    }
+
+    public static class UpgradeActionDeprecatedException extends IllegalArgumentException {
+        private final String path;
+        private final RestRequest.Method method;
+
+        public UpgradeActionDeprecatedException(RestRequest restRequest) {
+            this.path = restRequest.path();
+            this.method = restRequest.method();
+        }
+
+        @Override
+        public final String getMessage() {
+            return String.format(Locale.ROOT, "Upgrade action %s %s was removed, use _reindex API instead", method, path);
+        }
+    }
+}