remote/info should fail on node without remote_client role (#65289)

If a _remote/info request is executed on a node without the 
remote_cluster_client role, then we will always respond with an empty
result. With this commit, we will fail in such a request instead to
avoid confusing CCS and CCR users.

server/src/internalClusterTest/java/org/elasticsearch/action/admin/cluster/remote/RemoteInfoIT.java

@@ -0,0 +1,62 @@
+/*
+ * 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.action.admin.cluster.remote;
+
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
+import org.elasticsearch.test.AbstractMultiClustersTestCase;
+import org.elasticsearch.test.InternalTestCluster;
+import org.elasticsearch.test.NodeRoles;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class RemoteInfoIT extends AbstractMultiClustersTestCase {
+    @Override
+    protected Collection<String> remoteClusterAlias() {
+        if (randomBoolean()) {
+            return List.of();
+        } else {
+            return List.of("remote_cluster");
+        }
+    }
+
+    public void testRemoteClusterClientRole() {
+        final InternalTestCluster localCluster = cluster(LOCAL_CLUSTER);
+        localCluster.client().execute(RemoteInfoAction.INSTANCE, new RemoteInfoRequest()).actionGet();
+
+        final String nodeWithoutRemoteClientRole = localCluster.startNode(NodeRoles.onlyRoles(Set.of(DiscoveryNodeRole.DATA_ROLE)));
+        final IllegalArgumentException error = expectThrows(IllegalArgumentException.class, () ->
+            localCluster.client(nodeWithoutRemoteClientRole).execute(RemoteInfoAction.INSTANCE, new RemoteInfoRequest()).actionGet());
+        assertThat(error.getMessage(),
+            equalTo("node [" + nodeWithoutRemoteClientRole + "] does not have the [remote_cluster_client] role"));
+
+        final Set<DiscoveryNodeRole> roles = new HashSet<>();
+        roles.add(DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE);
+        if (randomBoolean()) {
+            roles.add(DiscoveryNodeRole.DATA_ROLE);
+        }
+        final String nodeWithRemoteClientRole = cluster(LOCAL_CLUSTER).startNode(NodeRoles.onlyRoles(roles));
+        localCluster.client(nodeWithRemoteClientRole).execute(RemoteInfoAction.INSTANCE, new RemoteInfoRequest()).actionGet();
+    }
+}

server/src/main/java/org/elasticsearch/action/admin/cluster/remote/TransportRemoteInfoAction.java

@@ -23,6 +23,7 @@ import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.search.SearchTransportService;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.HandledTransportAction;
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.transport.RemoteClusterService;
@@ -43,6 +44,10 @@ public final class TransportRemoteInfoAction extends HandledTransportAction<Remo
 
     @Override
     protected void doExecute(Task task, RemoteInfoRequest remoteInfoRequest, ActionListener<RemoteInfoResponse> listener) {
+        if (remoteClusterService.isEnabled() == false) {
+            throw new IllegalArgumentException("node [" + remoteClusterService.getLocalNode().getName() +
+                "] does not have the [" + DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE.roleName() + "] role");
+        }
         listener.onResponse(new RemoteInfoResponse(remoteClusterService.getRemoteConnectionInfos().collect(toList())));
     }
 }

server/src/main/java/org/elasticsearch/transport/RemoteClusterService.java

@@ -121,6 +121,10 @@ public final class RemoteClusterService extends RemoteClusterAware implements Cl
         this.transportService = transportService;
     }
 
+    public DiscoveryNode getLocalNode() {
+        return transportService.getLocalNode();
+    }
+
     /**
      * Returns <code>true</code> if at least one remote cluster is configured
      */