Remove unfreeze REST endpoint (#119227)

This adds a sentence to `redirects.asciidoc` explaining what frozen
indices were - otherwise, everything will point to the message about
the unfreeze API having gone away, which is not very helpful. Some
cross-references are updated to point to this rather than to the
notice about the removal of the unfreeze API.

ES-9736 #comment Removed `_unfreeze` REST endpoint in https://github.com/elastic/elasticsearch/pull/119227

docs/changelog/119227.yaml

@@ -0,0 +1,13 @@
+pr: 119227
+summary: Remove unfreeze REST endpoint
+area: Indices APIs
+type: breaking
+issues: []
+breaking:
+  title: Remove unfreeze REST endpoint
+  area: REST API
+  details: >-
+    The `/{index}/_unfreeze` REST endpoint is no longer supported. This API was deprecated, and the corresponding
+    `/{index}/_freeze` endpoint was removed in 8.0.
+  impact: None, since it is not possible to have a frozen index in a version which is readable by Elasticsearch 9.0
+  notable: false

docs/reference/indices.asciidoc

@@ -24,7 +24,6 @@ index settings, aliases, mappings, and index templates.
 * <<indices-split-index>>
 * <<indices-clone-index>>
 * <<indices-rollover-index>>
-* <<unfreeze-index-api>>
 * <<indices-resolve-index-api>>
 * <<indices-resolve-cluster-api>>
 * <<indices-downsample-data-stream>>
@@ -143,6 +142,5 @@ include::indices/shrink-index.asciidoc[]
 include::indices/simulate-index.asciidoc[]
 include::indices/simulate-template.asciidoc[]
 include::indices/split-index.asciidoc[]
-include::indices/apis/unfreeze.asciidoc[]
 include::indices/update-settings.asciidoc[]
 include::indices/put-mapping.asciidoc[]

docs/reference/indices/apis/unfreeze.asciidoc

@@ -1,61 +0,0 @@
-[role="xpack"]
-[[unfreeze-index-api]]
-=== Unfreeze index API
-++++
-<titleabbrev>Unfreeze index</titleabbrev>
-++++
-
-[WARNING]
-.Deprecated in 7.14
-====
-In 8.0, we removed the ability to freeze an index. In previous versions,
-freezing an index reduced its memory overhead. However, frozen indices are no
-longer useful due to
-https://www.elastic.co/blog/significantly-decrease-your-elasticsearch-heap-memory-usage[recent
-improvements in heap memory usage].
-You can use this API to unfreeze indices that were frozen in 7.x. Frozen indices
-are not related to the frozen data tier.
-====
-
-.New API reference
-[sidebar]
---
-For the most up-to-date API details, refer to {api-es}/group/endpoint-indices[Index APIs].
---
-
-Unfreezes an index.
-
-[[unfreeze-index-api-request]]
-==== {api-request-title}
-
-`POST /<index>/_unfreeze`
-
-[[unfreeze-index-api-prereqs]]
-==== {api-prereq-title}
-
-* If the {es} {security-features} are enabled, you must have the `manage`
-<<privileges-list-indices,index privilege>> for the target index or index alias.
-
-[[unfreeze-index-api-desc]]
-==== {api-description-title}
-
-When a frozen index is unfrozen, the index goes through the normal recovery
-process and becomes writeable again.
-
-[[unfreeze-index-api-path-parms]]
-==== {api-path-parms-title}
-
-`<index>`::
-  (Required, string) Identifier for the index.
-
-[[unfreeze-index-api-examples]]
-==== {api-examples-title}
-
-The following example unfreezes an index:
-
-[source,console]
---------------------------------------------------
-POST /my-index-000001/_unfreeze
---------------------------------------------------
-// TEST[s/^/PUT my-index-000001\n/]
-// TEST[skip:unable to ignore deprecation warning]

docs/reference/indices/index-mgmt.asciidoc

@@ -43,7 +43,7 @@ For more information on managing indices, refer to <<indices, Index APIs>>.
 
 * To filter the list of indices, use the search bar or click a badge.
 Badges indicate if an index is a <<ccr-put-follow,follower index>>, a
-<<rollup-get-rollup-index-caps,rollup index>>, or <<unfreeze-index-api,frozen>>.
+<<rollup-get-rollup-index-caps,rollup index>>, or <<frozen-indices,frozen>>.
 
 * To drill down into the index
 <<mapping,mappings>>, <<index-modules-settings,settings>>, and statistics,

docs/reference/redirects.asciidoc

@@ -156,10 +156,16 @@ See <<restore-entire-cluster>>.
 The freeze index API was removed in 8.0.
 // tag::frozen-removal-explanation[]
 Frozen indices are no longer useful due to
-https://www.elastic.co/blog/significantly-decrease-your-elasticsearch-heap-memory-usage[recent
-improvements in heap memory usage].
+https://www.elastic.co/blog/significantly-decrease-your-elasticsearch-heap-memory-usage[improvements
+in heap memory usage].
 // end::frozen-removal-explanation[]
 
+[role="exclude",id="unfreeze-index-api"]
+=== Unfreeze index API
+
+The unfreeze index API was removed in 9.0.
+include::redirects.asciidoc[tag=frozen-removal-explanation]
+
 [role="exclude",id="ilm-freeze"]
 === Freeze {ilm-init} action
 
@@ -1749,8 +1755,10 @@ See <<search-terms-enum>>.
 === Frozen indices
 
 // tag::frozen-index-redirect[]
-
-For API documentation, see <<unfreeze-index-api>>.
+Older versions of {es} provided the option to reduce the amount of data kept in memory for an index, at the expense of
+increasing search latency. This was known as 'freezing' the index.
+include::redirects.asciidoc[tag=frozen-removal-explanation]
+The freeze index API was removed in 8.0, and the unfreeze index API was removed in 9.0.
 // end::frozen-index-redirect[]
 
 [role="exclude",id="best_practices"]

docs/reference/sql/language/indices.asciidoc

@@ -100,7 +100,7 @@ requires the keyword `LIKE` for SQL `LIKE` pattern.
 [[sql-index-frozen]]
 === Frozen Indices
 
-By default, {es-sql} doesn't search <<unfreeze-index-api,frozen indices>>. To
+By default, {es-sql} doesn't search <<frozen-indices,frozen indices>>. To
 search frozen indices, use one of the following features:
 
 dedicated configuration parameter::

rest-api-spec/src/main/resources/rest-api-spec/api/indices.unfreeze.json

@@ -1,67 +0,0 @@
-{
-  "indices.unfreeze":{
-    "documentation":{
-      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/current/unfreeze-index-api.html",
-      "description":"Unfreezes an index. When a frozen index is unfrozen, the index goes through the normal recovery process and becomes writeable again."
-    },
-    "stability":"stable",
-    "visibility":"public",
-    "headers":{
-      "accept": [ "application/json"]
-    },
-    "url":{
-      "paths":[
-        {
-          "path":"/{index}/_unfreeze",
-          "methods":[
-            "POST"
-          ],
-          "parts":{
-            "index":{
-              "type":"string",
-              "description":"The name of the index to unfreeze"
-            }
-          },
-          "deprecated":{
-            "version":"7.14.0",
-            "description":"Frozen indices are deprecated because they provide no benefit given improvements in heap memory utilization. They will be removed in a future release."
-          }
-        }
-      ]
-    },
-    "params":{
-      "timeout":{
-        "type":"time",
-        "description":"Explicit operation timeout"
-      },
-      "master_timeout":{
-        "type":"time",
-        "description":"Specify timeout for connection to master"
-      },
-      "ignore_unavailable":{
-        "type":"boolean",
-        "description":"Whether specified concrete indices should be ignored when unavailable (missing or closed)"
-      },
-      "allow_no_indices":{
-        "type":"boolean",
-        "description":"Whether to ignore if a wildcard indices expression resolves into no concrete indices. (This includes `_all` string or when no indices have been specified)"
-      },
-      "expand_wildcards":{
-        "type":"enum",
-        "options":[
-          "open",
-          "closed",
-          "hidden",
-          "none",
-          "all"
-        ],
-        "default":"closed",
-        "description":"Whether to expand wildcard expression to concrete indices that are open, closed or both."
-      },
-      "wait_for_active_shards":{
-        "type":"string",
-        "description":"Sets the number of active shards to wait for before the operation returns."
-      }
-    }
-  }
-}

x-pack/plugin/frozen-indices/src/main/java/org/elasticsearch/xpack/frozen/FrozenIndices.java

@@ -8,36 +8,22 @@ package org.elasticsearch.xpack.frozen;
 
 import org.elasticsearch.action.ActionRequest;
 import org.elasticsearch.action.ActionResponse;
-import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
-import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
-import org.elasticsearch.common.settings.ClusterSettings;
-import org.elasticsearch.common.settings.IndexScopedSettings;
 import org.elasticsearch.common.settings.Setting;
-import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.common.settings.SettingsFilter;
-import org.elasticsearch.features.NodeFeature;
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.engine.EngineFactory;
 import org.elasticsearch.index.engine.frozen.FrozenEngine;
 import org.elasticsearch.plugins.ActionPlugin;
 import org.elasticsearch.plugins.EnginePlugin;
 import org.elasticsearch.plugins.Plugin;
-import org.elasticsearch.rest.RestController;
-import org.elasticsearch.rest.RestHandler;
 import org.elasticsearch.xpack.core.action.XPackInfoFeatureAction;
 import org.elasticsearch.xpack.core.action.XPackUsageFeatureAction;
 import org.elasticsearch.xpack.core.frozen.action.FreezeIndexAction;
 import org.elasticsearch.xpack.frozen.action.TransportFreezeIndexAction;
-import org.elasticsearch.xpack.frozen.rest.action.RestFreezeIndexAction;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
-import java.util.function.Predicate;
-import java.util.function.Supplier;
 
 public class FrozenIndices extends Plugin implements ActionPlugin, EnginePlugin {
 
@@ -63,19 +49,4 @@ public class FrozenIndices extends Plugin implements ActionPlugin, EnginePlugin
         actions.add(new ActionHandler<>(FreezeIndexAction.INSTANCE, TransportFreezeIndexAction.class));
         return actions;
     }
-
-    @Override
-    public List<RestHandler> getRestHandlers(
-        Settings settings,
-        NamedWriteableRegistry namedWriteableRegistry,
-        RestController restController,
-        ClusterSettings clusterSettings,
-        IndexScopedSettings indexScopedSettings,
-        SettingsFilter settingsFilter,
-        IndexNameExpressionResolver indexNameExpressionResolver,
-        Supplier<DiscoveryNodes> nodesInCluster,
-        Predicate<NodeFeature> clusterSupportsFeature
-    ) {
-        return Collections.singletonList(new RestFreezeIndexAction());
-    }
 }

x-pack/plugin/frozen-indices/src/main/java/org/elasticsearch/xpack/frozen/rest/action/RestFreezeIndexAction.java

@@ -1,67 +0,0 @@
-/*
- * 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; you may not use this file except in compliance with the Elastic License
- * 2.0.
- */
-package org.elasticsearch.xpack.frozen.rest.action;
-
-import org.elasticsearch.action.support.ActiveShardCount;
-import org.elasticsearch.action.support.IndicesOptions;
-import org.elasticsearch.client.internal.node.NodeClient;
-import org.elasticsearch.common.Strings;
-import org.elasticsearch.core.UpdateForV9;
-import org.elasticsearch.protocol.xpack.frozen.FreezeRequest;
-import org.elasticsearch.rest.BaseRestHandler;
-import org.elasticsearch.rest.RestRequest;
-import org.elasticsearch.rest.action.RestToXContentListener;
-import org.elasticsearch.xpack.core.frozen.action.FreezeIndexAction;
-
-import java.util.List;
-
-import static org.elasticsearch.rest.RestRequest.Method.POST;
-import static org.elasticsearch.rest.RestUtils.getAckTimeout;
-import static org.elasticsearch.rest.RestUtils.getMasterNodeTimeout;
-
-public final class RestFreezeIndexAction extends BaseRestHandler {
-
-    private static final String FREEZE_REMOVED = "It is no longer possible to freeze indices, but existing frozen indices can still be "
-        + "unfrozen";
-
-    private static final String UNFREEZE_DEPRECATED = "Frozen indices are deprecated because they provide no benefit given improvements "
-        + "in heap memory utilization. They will be removed in a future release.";
-
-    @UpdateForV9(owner = UpdateForV9.Owner.DISTRIBUTED_INDEXING)
-    // these routes were ".deprecated" in RestApiVersion.V_8 which will require use of REST API compatibility headers to access
-    // this API in v9. It is unclear if this was intentional for v9, and the code has been updated to ".deprecateAndKeep" which will
-    // continue to emit deprecations warnings but will not require any special headers to access the API in v9.
-    // Please review and update the code and tests as needed. The original code remains commented out below for reference.
-    @Override
-    public List<Route> routes() {
-        return List.of(
-            // Route.builder(POST, "/{index}/_unfreeze").deprecated(UNFREEZE_DEPRECATED, RestApiVersion.V_8).build()
-            Route.builder(POST, "/{index}/_unfreeze").deprecateAndKeep(UNFREEZE_DEPRECATED).build()
-        );
-    }
-
-    @Override
-    protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient client) {
-        final var freezeRequest = new FreezeRequest(
-            getMasterNodeTimeout(request),
-            getAckTimeout(request),
-            Strings.splitStringByCommaToArray(request.param("index"))
-        );
-        freezeRequest.indicesOptions(IndicesOptions.fromRequest(request, freezeRequest.indicesOptions()));
-        String waitForActiveShards = request.param("wait_for_active_shards");
-        if (waitForActiveShards != null) {
-            freezeRequest.waitForActiveShards(ActiveShardCount.parseString(waitForActiveShards));
-        }
-        freezeRequest.setFreeze(false);
-        return channel -> client.execute(FreezeIndexAction.INSTANCE, freezeRequest, new RestToXContentListener<>(channel));
-    }
-
-    @Override
-    public String getName() {
-        return "freeze_index";
-    }
-}