datafeed: check remote_cluster_client before cluster aliases in start

x-pack/plugin/ml/qa/datafeed-multicluster-tests/build.gradle

@@ -0,0 +1,11 @@
+apply plugin: 'elasticsearch.internal-java-rest-test'
+apply plugin: 'elasticsearch.rest-resources'
+
+dependencies {
+  testImplementation project(':x-pack:qa')
+  testImplementation project(path: ':test:test-clusters')
+}
+
+tasks.named('javaRestTest') {
+  usesDefaultDistribution("Test internally configures the clusters")
+}

x-pack/plugin/ml/qa/datafeed-multicluster-tests/src/javaRestTest/java/org/elasticsearch/xpack/ml/datafeed/DatafeedRemoteClusterClientIT.java

@@ -0,0 +1,177 @@
+/*
+ * 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", the "GNU Affero General Public License v3.0 only", 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", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.xpack.ml.datafeed;
+
+import org.apache.http.HttpHost;
+import org.elasticsearch.client.Request;
+import org.elasticsearch.client.Response;
+import org.elasticsearch.client.ResponseException;
+import org.elasticsearch.client.RestClient;
+import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.cluster.ElasticsearchCluster;
+import org.elasticsearch.test.cluster.local.distribution.DistributionType;
+import org.elasticsearch.test.rest.ESRestTestCase;
+import org.junit.ClassRule;
+import org.junit.rules.RuleChain;
+import org.junit.rules.TestRule;
+
+import java.io.IOException;
+
+import static org.hamcrest.Matchers.containsString;
+
+/**
+ * A test to check that remote_cluster_client errors are correctly reported when a datafeed job is started.
+ * The local datafeed job references a remote index in a local anomaly detection job. When the
+ * remote_cluster_client role is missing in the local cluster. This prevents remote indices from being
+ * resolved to their cluster names.
+ *
+ * @see <a href="https://github.com/elastic/elasticsearch/issues/121149">GitHub issue 121149</a>
+ */
+public class DatafeedRemoteClusterClientIT extends ESRestTestCase {
+    public static ElasticsearchCluster remoteCluster = ElasticsearchCluster.local()
+        .name("remote_cluster")
+        .distribution(DistributionType.DEFAULT)
+        .module("data-streams")
+        .module("x-pack-stack")
+        .setting("xpack.security.enabled", "false")
+        .setting("xpack.license.self_generated.type", "trial")
+        .setting("cluster.logsdb.enabled", "true")
+        .build();
+
+    public static ElasticsearchCluster localCluster = ElasticsearchCluster.local()
+        .name("local_cluster")
+        .distribution(DistributionType.DEFAULT)
+        .module("data-streams")
+        .module("x-pack-stack")
+        .setting("xpack.security.enabled", "false")
+        .setting("xpack.license.self_generated.type", "trial")
+        .setting("cluster.logsdb.enabled", "true")
+        .setting("node.roles", "[data,ingest,master,ml]") // remote_cluster_client not included
+        .setting("cluster.remote.remote_cluster.seeds", () -> "\"" + remoteCluster.getTransportEndpoint(0) + "\"")
+        .setting("cluster.remote.connections_per_cluster", "1")
+        .setting("cluster.remote.remote_cluster.skip_unavailable", "false")
+        .build();
+
+    @ClassRule
+    public static TestRule clusterRule = RuleChain.outerRule(remoteCluster).around(localCluster);
+
+    private RestClient localClusterClient() throws IOException {
+        var clusterHosts = parseClusterHosts(localCluster.getHttpAddresses());
+        return buildClient(restClientSettings(), clusterHosts.toArray(new HttpHost[0]));
+    }
+
+    private RestClient remoteClusterClient() throws IOException {
+        var clusterHosts = parseClusterHosts(remoteCluster.getHttpAddresses());
+        return buildClient(restClientSettings(), clusterHosts.toArray(new HttpHost[0]));
+    }
+
+    public void testSource() throws IOException {
+        String localIndex = "local_index";
+        String remoteIndex = "remote_index";
+        String mapping = """
+                {
+                    "properties": {
+                        "timestamp": {
+                            "type": "date"
+                        },
+                        "bytes": {
+                            "type": "integer"
+                        }
+                    }
+                }
+            """;
+        try (RestClient localClient = localClusterClient(); RestClient remoteClient = remoteClusterClient()) {
+            createIndex(
+                remoteClient,
+                remoteIndex,
+                Settings.builder().put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, between(5, 20)).build(),
+                mapping
+            );
+
+            Request request = new Request("PUT", "_ml/anomaly_detectors/test_anomaly_detector");
+            request.setJsonEntity("""
+                {
+                  "analysis_config": {
+                    "bucket_span": "15m",
+                    "detectors": [
+                      {
+                        "detector_description": "Sum of bytes",
+                        "function": "sum",
+                        "field_name": "bytes"
+                      }
+                    ]
+                  },
+                  "data_description": {
+                    "time_field": "timestamp",
+                    "time_format": "epoch_ms"
+                  },
+                  "analysis_limits": {
+                    "model_memory_limit": "11MB"
+                  },
+                  "model_plot_config": {
+                    "enabled": true,
+                    "annotations_enabled": true
+                  },
+                  "results_index_name": "test_datafeed_out",
+                  "datafeed_config": {
+                    "indices": [
+                      "remote_cluster:remote_index"
+                    ],
+                    "query": {
+                      "bool": {
+                        "must": [
+                          {
+                            "match_all": {}
+                          }
+                        ]
+                      }
+                    },
+                    "runtime_mappings": {
+                      "hour_of_day": {
+                        "type": "long",
+                        "script": {
+                          "source": "emit(doc['timestamp'].value.getHour());"
+                        }
+                      }
+                    },
+                    "datafeed_id": "test_datafeed"
+                  }
+                }""");
+            Response response = localClient.performRequest(request);
+            logger.info("Anomaly Detection Response:", response.getStatusLine());
+
+            request = new Request("GET", "_ml/anomaly_detectors/test_anomaly_detector");
+            response = localClient.performRequest(request);
+            logger.info("Anomaly detection get:", response.getEntity());
+
+            request = new Request("POST", "_ml/anomaly_detectors/test_anomaly_detector/_open");
+            response = localClient.performRequest(request);
+
+            final Request startRequest = new Request("POST", "_ml/datafeeds/test_datafeed/_start");
+            request.setJsonEntity("""
+                {
+                    "start": "2019-04-07T18:22:16Z"
+                }
+                """);
+            ResponseException e = assertThrows(ResponseException.class, () -> localClient.performRequest(startRequest));
+            assertThat(e.getMessage(), containsString("""
+                Datafeed [test_datafeed] is configured with a remote index pattern(s) \
+                [remote_cluster:remote_index] but the current node [local_cluster-0] \
+                is not allowed to connect to remote clusters. Please enable node.remote_cluster_client \
+                for all machine learning nodes and master-eligible nodes"""));
+        }
+    }
+
+    @Override
+    protected String getTestRestCluster() {
+        return localCluster.getHttpAddresses();
+    }
+}

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportStartDatafeedAction.java

@@ -227,6 +227,20 @@ public void onFailure(Exception e) {
         Consumer<Job> createDataExtractor = job -> {
             final List<String> remoteIndices = RemoteClusterLicenseChecker.remoteIndices(params.getDatafeedIndices());
             if (remoteIndices.isEmpty() == false) {
+                if (remoteClusterClient == false) {
+                    responseHeaderPreservingListener.onFailure(
+                        ExceptionsHelper.badRequestException(
+                            Messages.getMessage(
+                                Messages.DATAFEED_NEEDS_REMOTE_CLUSTER_SEARCH,
+                                datafeedConfigHolder.get().getId(),
+                                RemoteClusterLicenseChecker.remoteIndices(datafeedConfigHolder.get().getIndices()),
+                                clusterService.getNodeName()
+                            )
+                        )
+                    );
+                    return;
+                }
+
                 final RemoteClusterLicenseChecker remoteClusterLicenseChecker = new RemoteClusterLicenseChecker(
                     client,
                     MachineLearningField.ML_API_FEATURE
@@ -239,17 +253,6 @@ public void onFailure(Exception e) {
                     ActionListener.wrap(response -> {
                         if (response.isSuccess() == false) {
                             responseHeaderPreservingListener.onFailure(createUnlicensedError(params.getDatafeedId(), response));
-                        } else if (remoteClusterClient == false) {
-                            responseHeaderPreservingListener.onFailure(
-                                ExceptionsHelper.badRequestException(
-                                    Messages.getMessage(
-                                        Messages.DATAFEED_NEEDS_REMOTE_CLUSTER_SEARCH,
-                                        datafeedConfigHolder.get().getId(),
-                                        RemoteClusterLicenseChecker.remoteIndices(datafeedConfigHolder.get().getIndices()),
-                                        clusterService.getNodeName()
-                                    )
-                                )
-                            );
                         } else {
                             final RemoteClusterService remoteClusterService = transportService.getRemoteClusterService();
                             List<String> remoteAliases = RemoteClusterLicenseChecker.remoteClusterAliases(