CCS: Drop http address from remote cluster info

They are expensive to fetch and no longer needed by Kibana so they
*shouldn't* be needed by anyone else either.

Closes elastic#29207

docs/reference/cluster/remote-info.asciidoc

@@ -19,9 +19,6 @@ the configured remote cluster alias.
 `seeds`::
 	The configured initial seed transport addresses of the remote cluster.
 
-`http_addresses`::
-	The published http addresses of all connected remote nodes.
-
 `connected`::
 	True if there is at least one connection to the remote cluster.
 

docs/reference/release-notes/7.0.0-alpha1.asciidoc

@@ -8,4 +8,8 @@ The changes listed below have been released for the first time in Elasticsearch
 === Breaking changes
 
 Core::
-* Tribe node has been removed in favor of Cross-Cluster-Search
+* Tribe node has been removed in favor of Cross-Cluster-Search
+
+Cross-Cluster-Search::
+* `http_addresses` has been removed from the <<cluster-remote-info>> API
+  because it is expensive to fetch and no longer needed by Kibana.

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

@@ -30,6 +30,8 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 
+import static java.util.stream.Collectors.toList;
+
 public final class TransportRemoteInfoAction extends HandledTransportAction<RemoteInfoRequest, RemoteInfoResponse> {
 
     private final RemoteClusterService remoteClusterService;
@@ -45,7 +47,6 @@ public TransportRemoteInfoAction(Settings settings, ThreadPool threadPool, Trans
 
     @Override
     protected void doExecute(RemoteInfoRequest remoteInfoRequest, ActionListener<RemoteInfoResponse> listener) {
-        remoteClusterService.getRemoteConnectionInfos(ActionListener.wrap(remoteConnectionInfos
-                -> listener.onResponse(new RemoteInfoResponse(remoteConnectionInfos)), listener::onFailure));
+        listener.onResponse(new RemoteInfoResponse(remoteClusterService.getRemoteConnectionInfos().collect(toList())));
     }
 }

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestRemoteClusterInfoAction.java

@@ -32,6 +32,7 @@
 import org.elasticsearch.rest.RestResponse;
 import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.rest.action.RestBuilderListener;
+import org.elasticsearch.rest.action.RestToXContentListener;
 
 import java.io.IOException;
 
@@ -50,16 +51,8 @@ public String getName() {
     }
 
     @Override
-    public RestChannelConsumer prepareRequest(final RestRequest request, final NodeClient client)
-        throws IOException {
-        return channel -> client.execute(RemoteInfoAction.INSTANCE, new RemoteInfoRequest(),
-            new RestBuilderListener<RemoteInfoResponse>(channel) {
-            @Override
-            public RestResponse buildResponse(RemoteInfoResponse response, XContentBuilder builder) throws Exception {
-                response.toXContent(builder, request);
-                return new BytesRestResponse(RestStatus.OK, builder);
-            }
-        });
+    public RestChannelConsumer prepareRequest(final RestRequest request, final NodeClient client) throws IOException {
+        return channel -> client.execute(RemoteInfoAction.INSTANCE, new RemoteInfoRequest(), new RestToXContentListener<>(channel));
     }
     @Override
     public boolean canTripCircuitBreaker() {

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

@@ -40,6 +40,7 @@
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.transport.TransportAddress;
+import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.CancellableThreads;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
@@ -602,66 +603,13 @@ void addConnectedNode(DiscoveryNode node) {
     }
 
     /**
-     * Fetches connection info for this connection
+     * Get the information about remote nodes to be rendered on {@code _remote/info} requests.
      */
-    public void getConnectionInfo(ActionListener<RemoteConnectionInfo> listener) {
-        final Optional<DiscoveryNode> anyNode = connectedNodes.getAny();
-        if (anyNode.isPresent() == false) {
-            // not connected we return immediately
-            RemoteConnectionInfo remoteConnectionStats = new RemoteConnectionInfo(clusterAlias,
-                Collections.emptyList(), Collections.emptyList(), maxNumRemoteConnections, 0,
-                RemoteClusterService.REMOTE_INITIAL_CONNECTION_TIMEOUT_SETTING.get(settings), skipUnavailable);
-            listener.onResponse(remoteConnectionStats);
-        } else {
-            NodesInfoRequest request = new NodesInfoRequest();
-            request.clear();
-            request.http(true);
-
-            transportService.sendRequest(anyNode.get(), NodesInfoAction.NAME, request, new TransportResponseHandler<NodesInfoResponse>() {
-                @Override
-                public NodesInfoResponse newInstance() {
-                    return new NodesInfoResponse();
-                }
-
-                @Override
-                public void handleResponse(NodesInfoResponse response) {
-                    Collection<TransportAddress> httpAddresses = new HashSet<>();
-                    for (NodeInfo info : response.getNodes()) {
-                        if (connectedNodes.contains(info.getNode()) && info.getHttp() != null) {
-                            httpAddresses.add(info.getHttp().getAddress().publishAddress());
-                        }
-                    }
-
-                    if (httpAddresses.size() < maxNumRemoteConnections) {
-                        // just in case non of the connected nodes have http enabled we get other http enabled nodes instead.
-                        for (NodeInfo info : response.getNodes()) {
-                            if (nodePredicate.test(info.getNode()) && info.getHttp() != null) {
-                                httpAddresses.add(info.getHttp().getAddress().publishAddress());
-                            }
-                            if (httpAddresses.size() == maxNumRemoteConnections) {
-                                break; // once we have enough return...
-                            }
-                        }
-                    }
-                    RemoteConnectionInfo remoteConnectionInfo = new RemoteConnectionInfo(clusterAlias,
-                        seedNodes.stream().map(DiscoveryNode::getAddress).collect(Collectors.toList()), new ArrayList<>(httpAddresses),
-                        maxNumRemoteConnections, connectedNodes.size(),
-                        RemoteClusterService.REMOTE_INITIAL_CONNECTION_TIMEOUT_SETTING.get(settings), skipUnavailable);
-                    listener.onResponse(remoteConnectionInfo);
-                }
-
-                @Override
-                public void handleException(TransportException exp) {
-                    listener.onFailure(exp);
-                }
-
-                @Override
-                public String executor() {
-                    return ThreadPool.Names.SAME;
-                }
-            });
-        }
-
+    public RemoteConnectionInfo getConnectionInfo() {
+        List<TransportAddress> seedNodeAddresses = seedNodes.stream().map(DiscoveryNode::getAddress).collect(Collectors.toList());
+        TimeValue initialConnectionTimeout = RemoteClusterService.REMOTE_INITIAL_CONNECTION_TIMEOUT_SETTING.get(settings);
+        return new RemoteConnectionInfo(clusterAlias, seedNodeAddresses, maxNumRemoteConnections, connectedNodes.size(),
+                initialConnectionTimeout, skipUnavailable);
     }
 
     int getNumNodesConnected() {

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

@@ -42,6 +42,7 @@
 import java.io.Closeable;
 import java.io.IOException;
 import java.net.InetSocketAddress;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -56,6 +57,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static org.elasticsearch.common.settings.Setting.boolSetting;
 
@@ -348,17 +350,8 @@ public void close() throws IOException {
         IOUtils.close(remoteClusters.values());
     }
 
-    public void getRemoteConnectionInfos(ActionListener<Collection<RemoteConnectionInfo>> listener) {
-        final Map<String, RemoteClusterConnection> remoteClusters = this.remoteClusters;
-        if (remoteClusters.isEmpty()) {
-            listener.onResponse(Collections.emptyList());
-        } else {
-            final GroupedActionListener<RemoteConnectionInfo> actionListener = new GroupedActionListener<>(listener,
-                remoteClusters.size(), Collections.emptyList());
-            for (RemoteClusterConnection connection : remoteClusters.values()) {
-                connection.getConnectionInfo(actionListener);
-            }
-        }
+    public Stream<RemoteConnectionInfo> getRemoteConnectionInfos() {
+        return remoteClusters.values().stream().map(RemoteClusterConnection::getConnectionInfo);
     }
 
     /**

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

@@ -27,30 +27,29 @@
 import org.elasticsearch.common.xcontent.ToXContentFragment;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 
+import static java.util.Collections.emptyList;
+
 import java.io.IOException;
 import java.util.List;
 import java.util.Objects;
 
 /**
  * This class encapsulates all remote cluster information to be rendered on
- * <tt>_remote/info</tt> requests.
+ * {@code _remote/info} requests.
  */
 public final class RemoteConnectionInfo implements ToXContentFragment, Writeable {
     final List<TransportAddress> seedNodes;
-    final List<TransportAddress> httpAddresses;
     final int connectionsPerCluster;
     final TimeValue initialConnectionTimeout;
     final int numNodesConnected;
     final String clusterAlias;
     final boolean skipUnavailable;
 
     RemoteConnectionInfo(String clusterAlias, List<TransportAddress> seedNodes,
-                         List<TransportAddress> httpAddresses,
                          int connectionsPerCluster, int numNodesConnected,
                          TimeValue initialConnectionTimeout, boolean skipUnavailable) {
         this.clusterAlias = clusterAlias;
         this.seedNodes = seedNodes;
-        this.httpAddresses = httpAddresses;
         this.connectionsPerCluster = connectionsPerCluster;
         this.numNodesConnected = numNodesConnected;
         this.initialConnectionTimeout = initialConnectionTimeout;
@@ -59,16 +58,45 @@ public final class RemoteConnectionInfo implements ToXContentFragment, Writeable
 
     public RemoteConnectionInfo(StreamInput input) throws IOException {
         seedNodes = input.readList(TransportAddress::new);
-        httpAddresses = input.readList(TransportAddress::new);
+        if (input.getVersion().before(Version.V_7_0_0_alpha1)) {
+            /*
+             * Versions before 7.0 sent the HTTP addresses of all nodes in the
+             * remote cluster here but it was expensive to fetch and we
+             * ultimately figured out how to do without it. So we removed it.
+             *
+             * We just throw any HTTP addresses received here on the floor
+             * because we don't need to do anything with them.
+             */
+            input.readList(TransportAddress::new);
+        }
         connectionsPerCluster = input.readVInt();
         initialConnectionTimeout = input.readTimeValue();
         numNodesConnected = input.readVInt();
         clusterAlias = input.readString();
-        if (input.getVersion().onOrAfter(Version.V_6_1_0)) {
-            skipUnavailable = input.readBoolean();
-        } else {
-            skipUnavailable = false;
+        skipUnavailable = input.readBoolean();
+    }
+
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
+        out.writeList(seedNodes);
+        if (out.getVersion().before(Version.V_7_0_0_alpha1)) {
+            /*
+             * Versions before 7.0 sent the HTTP addresses of all nodes in the
+             * remote cluster here but it was expensive to fetch and we
+             * ultimately figured out how to do without it. So we removed it.
+             *
+             * When sending this request to a node that expects HTTP addresses
+             * here we pretend that we didn't find any. This *should* be fine
+             * because, after all, we haven't been using this information for
+             * a while.
+             */
+            out.writeList(emptyList());
         }
+        out.writeVInt(connectionsPerCluster);
+        out.writeTimeValue(initialConnectionTimeout);
+        out.writeVInt(numNodesConnected);
+        out.writeString(clusterAlias);
+        out.writeBoolean(skipUnavailable);
     }
 
     @Override
@@ -80,11 +108,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
                 builder.value(addr.toString());
             }
             builder.endArray();
-            builder.startArray("http_addresses");
-            for (TransportAddress addr : httpAddresses) {
-                builder.value(addr.toString());
-            }
-            builder.endArray();
             builder.field("connected", numNodesConnected > 0);
             builder.field("num_nodes_connected", numNodesConnected);
             builder.field("max_connections_per_cluster", connectionsPerCluster);
@@ -95,19 +118,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         return builder;
     }
 
-    @Override
-    public void writeTo(StreamOutput out) throws IOException {
-        out.writeList(seedNodes);
-        out.writeList(httpAddresses);
-        out.writeVInt(connectionsPerCluster);
-        out.writeTimeValue(initialConnectionTimeout);
-        out.writeVInt(numNodesConnected);
-        out.writeString(clusterAlias);
-        if (out.getVersion().onOrAfter(Version.V_6_1_0)) {
-            out.writeBoolean(skipUnavailable);
-        }
-    }
-
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;
@@ -116,15 +126,14 @@ public boolean equals(Object o) {
         return connectionsPerCluster == that.connectionsPerCluster &&
             numNodesConnected == that.numNodesConnected &&
             Objects.equals(seedNodes, that.seedNodes) &&
-            Objects.equals(httpAddresses, that.httpAddresses) &&
             Objects.equals(initialConnectionTimeout, that.initialConnectionTimeout) &&
             Objects.equals(clusterAlias, that.clusterAlias) &&
             skipUnavailable == that.skipUnavailable;
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(seedNodes, httpAddresses, connectionsPerCluster, initialConnectionTimeout,
+        return Objects.hash(seedNodes, connectionsPerCluster, initialConnectionTimeout,
                 numNodesConnected, clusterAlias, skipUnavailable);
     }
 }