[HLRC] Added support for Follow Stats API (#36253)

This change also adds documentation for the Follow Stats API.

Relates to #33824

client/rest-high-level/src/main/java/org/elasticsearch/client/CcrClient.java

@@ -23,6 +23,8 @@ import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.client.ccr.CcrStatsRequest;
 import org.elasticsearch.client.ccr.CcrStatsResponse;
 import org.elasticsearch.client.ccr.DeleteAutoFollowPatternRequest;
+import org.elasticsearch.client.ccr.FollowStatsRequest;
+import org.elasticsearch.client.ccr.FollowStatsResponse;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternRequest;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternResponse;
 import org.elasticsearch.client.ccr.PauseFollowRequest;
@@ -385,7 +387,7 @@ public final class CcrClient {
     }
 
     /**
-     * Gets all CCR stats.
+     * Asynchronously gets all CCR stats.
      *
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/ccr-get-stats.html">
      * the docs</a> for more.
@@ -406,4 +408,48 @@ public final class CcrClient {
         );
     }
 
+    /**
+     * Gets follow stats for specific indices.
+     *
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/ccr-get-follow-stats.html">
+     * the docs</a> for more.
+     *
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @return the response
+     * @throws IOException in case there is a problem sending the request or parsing back the response
+     */
+    public FollowStatsResponse getFollowStats(FollowStatsRequest request,
+                                              RequestOptions options) throws IOException {
+        return restHighLevelClient.performRequestAndParseEntity(
+            request,
+            CcrRequestConverters::getFollowStats,
+            options,
+            FollowStatsResponse::fromXContent,
+            Collections.emptySet()
+        );
+    }
+
+    /**
+     * Asynchronously gets follow stats for specific indices.
+     *
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/ccr-get-follow-stats.html">
+     * the docs</a> for more.
+     *
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     */
+    public void getFollowStatsAsync(FollowStatsRequest request,
+                                    RequestOptions options,
+                                    ActionListener<FollowStatsResponse> listener) {
+        restHighLevelClient.performRequestAsyncAndParseEntity(
+            request,
+            CcrRequestConverters::getFollowStats,
+            options,
+            FollowStatsResponse::fromXContent,
+            listener,
+            Collections.emptySet()
+        );
+    }
+
 }

client/rest-high-level/src/main/java/org/elasticsearch/client/CcrRequestConverters.java

@@ -25,6 +25,7 @@ import org.apache.http.client.methods.HttpPost;
 import org.apache.http.client.methods.HttpPut;
 import org.elasticsearch.client.ccr.CcrStatsRequest;
 import org.elasticsearch.client.ccr.DeleteAutoFollowPatternRequest;
+import org.elasticsearch.client.ccr.FollowStatsRequest;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternRequest;
 import org.elasticsearch.client.ccr.PauseFollowRequest;
 import org.elasticsearch.client.ccr.PutAutoFollowPatternRequest;
@@ -108,4 +109,12 @@ final class CcrRequestConverters {
         return new Request(HttpGet.METHOD_NAME, endpoint);
     }
 
+    static Request getFollowStats(FollowStatsRequest followStatsRequest) {
+        String endpoint = new RequestConverters.EndpointBuilder()
+            .addPathPart(followStatsRequest.getFollowerIndex())
+            .addPathPartAsIs("_ccr", "stats")
+            .build();
+        return new Request(HttpGet.METHOD_NAME, endpoint);
+    }
+
 }

client/rest-high-level/src/main/java/org/elasticsearch/client/ccr/FollowStatsRequest.java

@@ -0,0 +1,37 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.client.ccr;
+
+import org.elasticsearch.client.Validatable;
+
+import java.util.Objects;
+
+public final class FollowStatsRequest implements Validatable {
+
+    private final String followerIndex;
+
+    public FollowStatsRequest(String followerIndex) {
+        this.followerIndex = Objects.requireNonNull(followerIndex);
+    }
+
+    public String getFollowerIndex() {
+        return followerIndex;
+    }
+}

client/rest-high-level/src/main/java/org/elasticsearch/client/ccr/FollowStatsResponse.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.client.ccr;
+
+import org.elasticsearch.common.xcontent.XContentParser;
+
+public final class FollowStatsResponse {
+
+    public static FollowStatsResponse fromXContent(XContentParser parser) {
+        return new FollowStatsResponse(IndicesFollowStats.PARSER.apply(parser, null));
+    }
+
+    private final IndicesFollowStats indicesFollowStats;
+
+    public FollowStatsResponse(IndicesFollowStats indicesFollowStats) {
+        this.indicesFollowStats = indicesFollowStats;
+    }
+
+    public IndicesFollowStats getIndicesFollowStats() {
+        return indicesFollowStats;
+    }
+}

client/rest-high-level/src/test/java/org/elasticsearch/client/CCRIT.java

@@ -32,6 +32,8 @@ import org.elasticsearch.action.support.WriteRequest;
 import org.elasticsearch.client.ccr.CcrStatsRequest;
 import org.elasticsearch.client.ccr.CcrStatsResponse;
 import org.elasticsearch.client.ccr.DeleteAutoFollowPatternRequest;
+import org.elasticsearch.client.ccr.FollowStatsRequest;
+import org.elasticsearch.client.ccr.FollowStatsResponse;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternRequest;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternResponse;
 import org.elasticsearch.client.ccr.IndicesFollowStats.ShardFollowStats;
@@ -108,9 +110,10 @@ public class CCRIT extends ESRestHighLevelClientTestCase {
         assertThat(leaderSearchResponse.getHits().getTotalHits().value, equalTo(1L));
 
         assertBusy(() -> {
-            CcrStatsRequest ccrStatsRequest = new CcrStatsRequest();
-            CcrStatsResponse ccrStatsResponse = execute(ccrStatsRequest, ccrClient::getCcrStats, ccrClient::getCcrStatsAsync);
-            List<ShardFollowStats> shardFollowStats = ccrStatsResponse.getIndicesFollowStats().getShardFollowStats("follower");
+            FollowStatsRequest followStatsRequest = new FollowStatsRequest("follower");
+            FollowStatsResponse followStatsResponse =
+                execute(followStatsRequest, ccrClient::getFollowStats, ccrClient::getFollowStatsAsync);
+            List<ShardFollowStats> shardFollowStats = followStatsResponse.getIndicesFollowStats().getShardFollowStats("follower");
             long followerGlobalCheckpoint = shardFollowStats.stream()
                 .mapToLong(ShardFollowStats::getFollowerGlobalCheckpoint)
                 .max()
@@ -133,9 +136,10 @@ public class CCRIT extends ESRestHighLevelClientTestCase {
         assertThat(resumeFollowResponse.isAcknowledged(), is(true));
 
         assertBusy(() -> {
-            CcrStatsRequest ccrStatsRequest = new CcrStatsRequest();
-            CcrStatsResponse ccrStatsResponse = execute(ccrStatsRequest, ccrClient::getCcrStats, ccrClient::getCcrStatsAsync);
-            List<ShardFollowStats> shardFollowStats = ccrStatsResponse.getIndicesFollowStats().getShardFollowStats("follower");
+            FollowStatsRequest followStatsRequest = new FollowStatsRequest("follower");
+            FollowStatsResponse followStatsResponse =
+                execute(followStatsRequest, ccrClient::getFollowStats, ccrClient::getFollowStatsAsync);
+            List<ShardFollowStats> shardFollowStats = followStatsResponse.getIndicesFollowStats().getShardFollowStats("follower");
             long followerGlobalCheckpoint = shardFollowStats.stream()
                 .mapToLong(ShardFollowStats::getFollowerGlobalCheckpoint)
                 .max()

client/rest-high-level/src/test/java/org/elasticsearch/client/ccr/CcrStatsResponseTests.java

@@ -323,7 +323,7 @@ public class CcrStatsResponseTests extends ESTestCase {
         );
     }
 
-    private static IndicesFollowStats randomIndicesFollowStats() {
+    static IndicesFollowStats randomIndicesFollowStats() {
         int numIndices = randomIntBetween(0, 16);
         NavigableMap<String, List<ShardFollowStats>> shardFollowStats = new TreeMap<>();
         for (int i = 0; i < numIndices; i++) {

client/rest-high-level/src/test/java/org/elasticsearch/client/ccr/FollowStatsResponseTests.java

@@ -0,0 +1,253 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.client.ccr;
+
+import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.client.ccr.IndicesFollowStats.ShardFollowStats;
+import org.elasticsearch.common.collect.Tuple;
+import org.elasticsearch.common.unit.ByteSizeUnit;
+import org.elasticsearch.common.unit.ByteSizeValue;
+import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.test.ESTestCase;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+import static org.elasticsearch.client.ccr.CcrStatsResponseTests.randomIndicesFollowStats;
+import static org.elasticsearch.test.AbstractXContentTestCase.xContentTester;
+import static org.hamcrest.Matchers.anyOf;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.instanceOf;
+
+public class FollowStatsResponseTests extends ESTestCase {
+
+    public void testFromXContent() throws IOException {
+        xContentTester(this::createParser,
+            FollowStatsResponseTests::createTestInstance,
+            FollowStatsResponseTests::toXContent,
+            FollowStatsResponse::fromXContent)
+            .supportsUnknownFields(false)
+            .assertEqualsConsumer(FollowStatsResponseTests::assertEqualInstances)
+            .assertToXContentEquivalence(false)
+            .test();
+    }
+
+    // Needed, because exceptions in IndicesFollowStats cannot be compared
+    private static void assertEqualInstances(FollowStatsResponse expectedInstance, FollowStatsResponse newInstance) {
+        assertNotSame(expectedInstance, newInstance);
+        {
+            IndicesFollowStats newIndicesFollowStats = newInstance.getIndicesFollowStats();
+            IndicesFollowStats expectedIndicesFollowStats = expectedInstance.getIndicesFollowStats();
+            assertThat(newIndicesFollowStats.getShardFollowStats().size(),
+                equalTo(expectedIndicesFollowStats.getShardFollowStats().size()));
+            assertThat(newIndicesFollowStats.getShardFollowStats().keySet(),
+                equalTo(expectedIndicesFollowStats.getShardFollowStats().keySet()));
+            for (Map.Entry<String, List<ShardFollowStats>> indexEntry : newIndicesFollowStats.getShardFollowStats().entrySet()) {
+                List<ShardFollowStats> newStats = indexEntry.getValue();
+                List<ShardFollowStats> expectedStats = expectedIndicesFollowStats.getShardFollowStats(indexEntry.getKey());
+                assertThat(newStats.size(), equalTo(expectedStats.size()));
+                for (int i = 0; i < newStats.size(); i++) {
+                    ShardFollowStats actualShardFollowStats = newStats.get(i);
+                    ShardFollowStats expectedShardFollowStats = expectedStats.get(i);
+
+                    assertThat(actualShardFollowStats.getRemoteCluster(), equalTo(expectedShardFollowStats.getRemoteCluster()));
+                    assertThat(actualShardFollowStats.getLeaderIndex(), equalTo(expectedShardFollowStats.getLeaderIndex()));
+                    assertThat(actualShardFollowStats.getFollowerIndex(), equalTo(expectedShardFollowStats.getFollowerIndex()));
+                    assertThat(actualShardFollowStats.getShardId(), equalTo(expectedShardFollowStats.getShardId()));
+                    assertThat(actualShardFollowStats.getLeaderGlobalCheckpoint(),
+                        equalTo(expectedShardFollowStats.getLeaderGlobalCheckpoint()));
+                    assertThat(actualShardFollowStats.getLeaderMaxSeqNo(), equalTo(expectedShardFollowStats.getLeaderMaxSeqNo()));
+                    assertThat(actualShardFollowStats.getFollowerGlobalCheckpoint(),
+                        equalTo(expectedShardFollowStats.getFollowerGlobalCheckpoint()));
+                    assertThat(actualShardFollowStats.getLastRequestedSeqNo(), equalTo(expectedShardFollowStats.getLastRequestedSeqNo()));
+                    assertThat(actualShardFollowStats.getOutstandingReadRequests(),
+                        equalTo(expectedShardFollowStats.getOutstandingReadRequests()));
+                    assertThat(actualShardFollowStats.getOutstandingWriteRequests(),
+                        equalTo(expectedShardFollowStats.getOutstandingWriteRequests()));
+                    assertThat(actualShardFollowStats.getWriteBufferOperationCount(),
+                        equalTo(expectedShardFollowStats.getWriteBufferOperationCount()));
+                    assertThat(actualShardFollowStats.getFollowerMappingVersion(),
+                        equalTo(expectedShardFollowStats.getFollowerMappingVersion()));
+                    assertThat(actualShardFollowStats.getFollowerSettingsVersion(),
+                        equalTo(expectedShardFollowStats.getFollowerSettingsVersion()));
+                    assertThat(actualShardFollowStats.getTotalReadTimeMillis(),
+                        equalTo(expectedShardFollowStats.getTotalReadTimeMillis()));
+                    assertThat(actualShardFollowStats.getSuccessfulReadRequests(),
+                        equalTo(expectedShardFollowStats.getSuccessfulReadRequests()));
+                    assertThat(actualShardFollowStats.getFailedReadRequests(), equalTo(expectedShardFollowStats.getFailedReadRequests()));
+                    assertThat(actualShardFollowStats.getOperationsReads(), equalTo(expectedShardFollowStats.getOperationsReads()));
+                    assertThat(actualShardFollowStats.getBytesRead(), equalTo(expectedShardFollowStats.getBytesRead()));
+                    assertThat(actualShardFollowStats.getTotalWriteTimeMillis(),
+                        equalTo(expectedShardFollowStats.getTotalWriteTimeMillis()));
+                    assertThat(actualShardFollowStats.getSuccessfulWriteRequests(),
+                        equalTo(expectedShardFollowStats.getSuccessfulWriteRequests()));
+                    assertThat(actualShardFollowStats.getFailedWriteRequests(),
+                        equalTo(expectedShardFollowStats.getFailedWriteRequests()));
+                    assertThat(actualShardFollowStats.getOperationWritten(), equalTo(expectedShardFollowStats.getOperationWritten()));
+                    assertThat(actualShardFollowStats.getReadExceptions().size(),
+                        equalTo(expectedShardFollowStats.getReadExceptions().size()));
+                    assertThat(actualShardFollowStats.getReadExceptions().keySet(),
+                        equalTo(expectedShardFollowStats.getReadExceptions().keySet()));
+                    for (final Map.Entry<Long, Tuple<Integer, ElasticsearchException>> entry :
+                        actualShardFollowStats.getReadExceptions().entrySet()) {
+                        final Tuple<Integer, ElasticsearchException> expectedTuple =
+                            expectedShardFollowStats.getReadExceptions().get(entry.getKey());
+                        assertThat(entry.getValue().v1(), equalTo(expectedTuple.v1()));
+                        // x-content loses the exception
+                        final ElasticsearchException expected = expectedTuple.v2();
+                        assertThat(entry.getValue().v2().getMessage(), containsString(expected.getMessage()));
+                        assertNotNull(entry.getValue().v2().getCause());
+                        assertThat(
+                            entry.getValue().v2().getCause(),
+                            anyOf(instanceOf(ElasticsearchException.class), instanceOf(IllegalStateException.class)));
+                        assertThat(entry.getValue().v2().getCause().getMessage(), containsString(expected.getCause().getMessage()));
+                    }
+                    assertThat(actualShardFollowStats.getTimeSinceLastReadMillis(),
+                        equalTo(expectedShardFollowStats.getTimeSinceLastReadMillis()));
+                }
+            }
+        }
+    }
+
+    private static void toXContent(FollowStatsResponse response, XContentBuilder builder) throws IOException {
+        builder.startObject();
+        {
+            builder.startArray(IndicesFollowStats.INDICES_FIELD.getPreferredName());
+            for (Map.Entry<String, List<ShardFollowStats>> indexEntry :
+                response.getIndicesFollowStats().getShardFollowStats().entrySet()) {
+                builder.startObject();
+                {
+                    builder.field(IndicesFollowStats.INDEX_FIELD.getPreferredName(), indexEntry.getKey());
+                    builder.startArray(IndicesFollowStats.SHARDS_FIELD.getPreferredName());
+                    {
+                        for (ShardFollowStats stats : indexEntry.getValue()) {
+                            builder.startObject();
+                            {
+                                builder.field(ShardFollowStats.LEADER_CLUSTER.getPreferredName(), stats.getRemoteCluster());
+                                builder.field(ShardFollowStats.LEADER_INDEX.getPreferredName(), stats.getLeaderIndex());
+                                builder.field(ShardFollowStats.FOLLOWER_INDEX.getPreferredName(), stats.getFollowerIndex());
+                                builder.field(ShardFollowStats.SHARD_ID.getPreferredName(), stats.getShardId());
+                                builder.field(ShardFollowStats.LEADER_GLOBAL_CHECKPOINT_FIELD.getPreferredName(),
+                                    stats.getLeaderGlobalCheckpoint());
+                                builder.field(ShardFollowStats.LEADER_MAX_SEQ_NO_FIELD.getPreferredName(), stats.getLeaderMaxSeqNo());
+                                builder.field(ShardFollowStats.FOLLOWER_GLOBAL_CHECKPOINT_FIELD.getPreferredName(),
+                                    stats.getFollowerGlobalCheckpoint());
+                                builder.field(ShardFollowStats.FOLLOWER_MAX_SEQ_NO_FIELD.getPreferredName(),
+                                    stats.getFollowerMaxSeqNo());
+                                builder.field(ShardFollowStats.LAST_REQUESTED_SEQ_NO_FIELD.getPreferredName(),
+                                    stats.getLastRequestedSeqNo());
+                                builder.field(ShardFollowStats.OUTSTANDING_READ_REQUESTS.getPreferredName(),
+                                    stats.getOutstandingReadRequests());
+                                builder.field(ShardFollowStats.OUTSTANDING_WRITE_REQUESTS.getPreferredName(),
+                                    stats.getOutstandingWriteRequests());
+                                builder.field(ShardFollowStats.WRITE_BUFFER_OPERATION_COUNT_FIELD.getPreferredName(),
+                                    stats.getWriteBufferOperationCount());
+                                builder.humanReadableField(
+                                    ShardFollowStats.WRITE_BUFFER_SIZE_IN_BYTES_FIELD.getPreferredName(),
+                                    "write_buffer_size",
+                                    new ByteSizeValue(stats.getWriteBufferSizeInBytes()));
+                                builder.field(ShardFollowStats.FOLLOWER_MAPPING_VERSION_FIELD.getPreferredName(),
+                                    stats.getFollowerMappingVersion());
+                                builder.field(ShardFollowStats.FOLLOWER_SETTINGS_VERSION_FIELD.getPreferredName(),
+                                    stats.getFollowerSettingsVersion());
+                                builder.humanReadableField(
+                                    ShardFollowStats.TOTAL_READ_TIME_MILLIS_FIELD.getPreferredName(),
+                                    "total_read_time",
+                                    new TimeValue(stats.getTotalReadTimeMillis(), TimeUnit.MILLISECONDS));
+                                builder.humanReadableField(
+                                    ShardFollowStats.TOTAL_READ_REMOTE_EXEC_TIME_MILLIS_FIELD.getPreferredName(),
+                                    "total_read_remote_exec_time",
+                                    new TimeValue(stats.getTotalReadRemoteExecTimeMillis(), TimeUnit.MILLISECONDS));
+                                builder.field(ShardFollowStats.SUCCESSFUL_READ_REQUESTS_FIELD.getPreferredName(),
+                                    stats.getSuccessfulReadRequests());
+                                builder.field(ShardFollowStats.FAILED_READ_REQUESTS_FIELD.getPreferredName(),
+                                    stats.getFailedReadRequests());
+                                builder.field(ShardFollowStats.OPERATIONS_READ_FIELD.getPreferredName(), stats.getOperationsReads());
+                                builder.humanReadableField(
+                                    ShardFollowStats.BYTES_READ.getPreferredName(),
+                                    "total_read",
+                                    new ByteSizeValue(stats.getBytesRead(), ByteSizeUnit.BYTES));
+                                builder.humanReadableField(
+                                    ShardFollowStats.TOTAL_WRITE_TIME_MILLIS_FIELD.getPreferredName(),
+                                    "total_write_time",
+                                    new TimeValue(stats.getTotalWriteTimeMillis(), TimeUnit.MILLISECONDS));
+                                builder.field(ShardFollowStats.SUCCESSFUL_WRITE_REQUESTS_FIELD.getPreferredName(),
+                                    stats.getSuccessfulWriteRequests());
+                                builder.field(ShardFollowStats.FAILED_WRITE_REQUEST_FIELD.getPreferredName(),
+                                    stats.getFailedWriteRequests());
+                                builder.field(ShardFollowStats.OPERATIONS_WRITTEN.getPreferredName(), stats.getOperationWritten());
+                                builder.startArray(ShardFollowStats.READ_EXCEPTIONS.getPreferredName());
+                                {
+                                    for (final Map.Entry<Long, Tuple<Integer, ElasticsearchException>> entry :
+                                        stats.getReadExceptions().entrySet()) {
+                                        builder.startObject();
+                                        {
+                                            builder.field(ShardFollowStats.READ_EXCEPTIONS_ENTRY_FROM_SEQ_NO.getPreferredName(),
+                                                entry.getKey());
+                                            builder.field(ShardFollowStats.READ_EXCEPTIONS_RETRIES.getPreferredName(),
+                                                entry.getValue().v1());
+                                            builder.field(ShardFollowStats.READ_EXCEPTIONS_ENTRY_EXCEPTION.getPreferredName());
+                                            builder.startObject();
+                                            {
+                                                ElasticsearchException.generateThrowableXContent(builder, ToXContent.EMPTY_PARAMS,
+                                                    entry.getValue().v2());
+                                            }
+                                            builder.endObject();
+                                        }
+                                        builder.endObject();
+                                    }
+                                }
+                                builder.endArray();
+                                builder.humanReadableField(
+                                    ShardFollowStats.TIME_SINCE_LAST_READ_MILLIS_FIELD.getPreferredName(),
+                                    "time_since_last_read",
+                                    new TimeValue(stats.getTimeSinceLastReadMillis(), TimeUnit.MILLISECONDS));
+                                if (stats.getFatalException() != null) {
+                                    builder.field(ShardFollowStats.FATAL_EXCEPTION.getPreferredName());
+                                    builder.startObject();
+                                    {
+                                        ElasticsearchException.generateThrowableXContent(builder, ToXContent.EMPTY_PARAMS,
+                                            stats.getFatalException());
+                                    }
+                                    builder.endObject();
+                                }
+                            }
+                            builder.endObject();
+                        }
+                    }
+                    builder.endArray();
+                }
+                builder.endObject();
+            }
+            builder.endArray();
+        }
+        builder.endObject();
+    }
+
+    private static FollowStatsResponse createTestInstance() {
+        return new FollowStatsResponse(randomIndicesFollowStats());
+    }
+
+}

client/rest-high-level/src/test/java/org/elasticsearch/client/documentation/CCRDocumentationIT.java

@@ -37,6 +37,8 @@ import org.elasticsearch.client.ccr.AutoFollowStats;
 import org.elasticsearch.client.ccr.CcrStatsRequest;
 import org.elasticsearch.client.ccr.CcrStatsResponse;
 import org.elasticsearch.client.ccr.DeleteAutoFollowPatternRequest;
+import org.elasticsearch.client.ccr.FollowStatsRequest;
+import org.elasticsearch.client.ccr.FollowStatsResponse;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternRequest;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternResponse;
 import org.elasticsearch.client.ccr.GetAutoFollowPatternResponse.Pattern;
@@ -622,6 +624,51 @@ public class CCRDocumentationIT extends ESRestHighLevelClientTestCase {
         assertTrue(latch.await(30L, TimeUnit.SECONDS));
     }
 
+    public void testGetFollowStats() throws Exception {
+        RestHighLevelClient client = highLevelClient();
+
+        // tag::ccr-get-follow-stats-request
+        FollowStatsRequest request =
+            new FollowStatsRequest("follower"); // <1>
+        // end::ccr-get-follow-stats-request
+
+        // tag::ccr-get-follow-stats-execute
+        FollowStatsResponse response = client.ccr()
+            .getFollowStats(request, RequestOptions.DEFAULT);
+        // end::ccr-get-follow-stats-execute
+
+        // tag::ccr-get-follow-stats-response
+        IndicesFollowStats indicesFollowStats =
+            response.getIndicesFollowStats(); // <1>
+        // end::ccr-get-follow-stats-response
+
+        // tag::ccr-get-follow-stats-execute-listener
+        ActionListener<FollowStatsResponse> listener =
+            new ActionListener<FollowStatsResponse>() {
+                @Override
+                public void onResponse(FollowStatsResponse response) { // <1>
+                    IndicesFollowStats indicesFollowStats =
+                        response.getIndicesFollowStats();
+                }
+
+                @Override
+                public void onFailure(Exception e) {
+                    // <2>
+                }
+            };
+        // end::ccr-get-follow-stats-execute-listener
+
+        // Replace the empty listener by a blocking listener in test
+        final CountDownLatch latch = new CountDownLatch(1);
+        listener = new LatchedActionListener<>(listener, latch);
+
+        // tag::ccr-get-follow-stats-execute-async
+        client.ccr().getFollowStatsAsync(request,
+            RequestOptions.DEFAULT, listener); // <1>
+        // end::ccr-get-follow-stats-execute-async
+
+        assertTrue(latch.await(30L, TimeUnit.SECONDS));
+    }
 
     static Map<String, Object> toMap(Response response) throws IOException {
         return XContentHelper.convertToMap(JsonXContent.jsonXContent, EntityUtils.toString(response.getEntity()), false);

docs/java-rest/high-level/ccr/get_follow_stats.asciidoc

@@ -0,0 +1,35 @@
+--
+:api: ccr-get-follow-stats
+:request: FollowStatsRequest
+:response: FollowStatsResponse
+--
+
+[id="{upid}-{api}"]
+=== Get Follow Stats API
+
+
+[id="{upid}-{api}-request"]
+==== Request
+
+The Get Follow Stats API allows you to get follow statistics for specific follower indices.
+
+["source","java",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{doc-tests-file}[{api}-request]
+--------------------------------------------------
+<1> The follower index to get follow statistics for.
+
+[id="{upid}-{api}-response"]
+==== Response
+
+The returned +{response}+ includes follow statistics for the specified follower indices
+
+["source","java",subs="attributes,callouts,macros"]
+--------------------------------------------------
+include-tagged::{doc-tests-file}[{api}-response]
+--------------------------------------------------
+<1> The follow stats for specified follower indices.
+
+include::../execution.asciidoc[]
+
+

docs/java-rest/high-level/supported-apis.asciidoc

@@ -486,6 +486,7 @@ The Java High Level REST Client supports the following CCR APIs:
 * <<{upid}-ccr-delete-auto-follow-pattern>>
 * <<{upid}-ccr-get-auto-follow-pattern>>
 * <<{upid}-ccr-get-stats>>
+* <<{upid}-ccr-get-follow-stats>>
 
 include::ccr/put_follow.asciidoc[]
 include::ccr/pause_follow.asciidoc[]
@@ -495,6 +496,7 @@ include::ccr/put_auto_follow_pattern.asciidoc[]
 include::ccr/delete_auto_follow_pattern.asciidoc[]
 include::ccr/get_auto_follow_pattern.asciidoc[]
 include::ccr/get_stats.asciidoc[]
+include::ccr/get_follow_stats.asciidoc[]
 
 == Index Lifecycle Management APIs