Allow simple connection strategy to be configured (elastic#49066)

Currently the simple connection strategy only exists in the code. It
cannot be configured. This commit moves in the direction of allowing it
to be configured. It introduces settings for the addresses and socket
count. Additionally it introduces new settings for the sniff strategy
so that the more generic number of connections and seed node settings
can be deprecated.

The simple settings are not yet registered as the registration is
dependent on follow-up work to validate the settings.

Author: Tim-Brooks

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

@@ -83,7 +83,7 @@ public void setupRemoteClusterConfig() throws Exception {
         String transportAddress = (String) nodesResponse.get("transport_address");
 
         ClusterUpdateSettingsRequest updateSettingsRequest = new ClusterUpdateSettingsRequest();
-        updateSettingsRequest.transientSettings(Collections.singletonMap("cluster.remote.local_cluster.seeds", transportAddress));
+        updateSettingsRequest.transientSettings(Collections.singletonMap("cluster.remote.local_cluster.sniff.seeds", transportAddress));
         ClusterUpdateSettingsResponse updateSettingsResponse =
             highLevelClient().cluster().putSettings(updateSettingsRequest, RequestOptions.DEFAULT);
         assertThat(updateSettingsResponse.isAcknowledged(), is(true));

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

@@ -87,7 +87,7 @@ public void setupRemoteClusterConfig() throws IOException {
         String transportAddress = (String) nodesResponse.get("transport_address");
 
         ClusterUpdateSettingsRequest updateSettingsRequest = new ClusterUpdateSettingsRequest();
-        updateSettingsRequest.transientSettings(Collections.singletonMap("cluster.remote.local.seeds", transportAddress));
+        updateSettingsRequest.transientSettings(Collections.singletonMap("cluster.remote.local.sniff.seeds", transportAddress));
         ClusterUpdateSettingsResponse updateSettingsResponse =
             client.cluster().putSettings(updateSettingsRequest, RequestOptions.DEFAULT);
         assertThat(updateSettingsResponse.isAcknowledged(), is(true));

qa/ccs-unavailable-clusters/src/test/java/org/elasticsearch/search/CrossClusterSearchUnavailableClusterIT.java

@@ -144,7 +144,7 @@ public void testSearchSkipUnavailable() throws IOException {
         try (MockTransportService remoteTransport = startTransport("node0", new CopyOnWriteArrayList<>(), Version.CURRENT, threadPool)) {
             DiscoveryNode remoteNode = remoteTransport.getLocalDiscoNode();
 
-            updateRemoteClusterSettings(Collections.singletonMap("seeds", remoteNode.getAddress().toString()));
+            updateRemoteClusterSettings(Collections.singletonMap("sniff.seeds", remoteNode.getAddress().toString()));
 
             for (int i = 0; i < 10; i++) {
                 restHighLevelClient.index(
@@ -229,7 +229,7 @@ public void testSearchSkipUnavailable() throws IOException {
             assertSearchConnectFailure();
 
             Map<String, Object> map = new HashMap<>();
-            map.put("seeds", null);
+            map.put("sniff.seeds", null);
             map.put("skip_unavailable", null);
             updateRemoteClusterSettings(map);
         }
@@ -248,32 +248,32 @@ public void testSkipUnavailableDependsOnSeeds() throws IOException {
                         () -> client().performRequest(request));
                 assertEquals(400, responseException.getResponse().getStatusLine().getStatusCode());
                 assertThat(responseException.getMessage(),
-                        containsString("missing required setting [cluster.remote.remote1.seeds] " +
+                        containsString("missing required setting [cluster.remote.remote1.sniff.seeds] " +
                                 "for setting [cluster.remote.remote1.skip_unavailable]"));
             }
 
             Map<String, Object> settingsMap = new HashMap<>();
-            settingsMap.put("seeds", remoteNode.getAddress().toString());
+            settingsMap.put("sniff.seeds", remoteNode.getAddress().toString());
             settingsMap.put("skip_unavailable", randomBoolean());
             updateRemoteClusterSettings(settingsMap);
 
             {
                 //check that seeds cannot be reset alone if skip_unavailable is set
                 Request request = new Request("PUT", "/_cluster/settings");
-                request.setEntity(buildUpdateSettingsRequestBody(Collections.singletonMap("seeds", null)));
+                request.setEntity(buildUpdateSettingsRequestBody(Collections.singletonMap("sniff.seeds", null)));
                 ResponseException responseException = expectThrows(ResponseException.class,
                         () -> client().performRequest(request));
                 assertEquals(400, responseException.getResponse().getStatusLine().getStatusCode());
-                assertThat(responseException.getMessage(), containsString("missing required setting [cluster.remote.remote1.seeds] " +
+                assertThat(responseException.getMessage(), containsString("missing required setting [cluster.remote.remote1.sniff.seeds] " +
                         "for setting [cluster.remote.remote1.skip_unavailable]"));
             }
 
             if (randomBoolean()) {
                 updateRemoteClusterSettings(Collections.singletonMap("skip_unavailable", null));
-                updateRemoteClusterSettings(Collections.singletonMap("seeds", null));
+                updateRemoteClusterSettings(Collections.singletonMap("sniff.seeds", null));
             } else {
                 Map<String, Object> nullMap = new HashMap<>();
-                nullMap.put("seeds", null);
+                nullMap.put("sniff.seeds", null);
                 nullMap.put("skip_unavailable", null);
                 updateRemoteClusterSettings(nullMap);
             }

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -110,6 +110,7 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.RemoteClusterAware;
 import org.elasticsearch.transport.RemoteClusterService;
+import org.elasticsearch.transport.SniffConnectionStrategy;
 import org.elasticsearch.transport.TransportSettings;
 import org.elasticsearch.watcher.ResourceWatcherService;
 
@@ -303,10 +304,8 @@ public void apply(Settings value, Settings current, Settings previous) {
             SearchService.DEFAULT_ALLOW_PARTIAL_SEARCH_RESULTS,
             ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING,
             TransportSearchAction.SHARD_COUNT_LIMIT_SETTING,
-            RemoteClusterAware.REMOTE_CLUSTERS_SEEDS,
             RemoteClusterAware.SEARCH_REMOTE_CLUSTERS_SEEDS,
-            RemoteClusterAware.REMOTE_CLUSTERS_PROXY,
-            RemoteClusterAware.SEARCH_REMOTE_CLUSTERS_PROXY,
+            SniffConnectionStrategy.SEARCH_REMOTE_CLUSTERS_PROXY,
             RemoteClusterService.REMOTE_CLUSTER_SKIP_UNAVAILABLE,
             RemoteClusterService.SEARCH_REMOTE_CLUSTER_SKIP_UNAVAILABLE,
             RemoteClusterService.REMOTE_CONNECTIONS_PER_CLUSTER,
@@ -319,6 +318,10 @@ public void apply(Settings value, Settings current, Settings previous) {
             RemoteClusterService.SEARCH_ENABLE_REMOTE_CLUSTERS,
             RemoteClusterService.REMOTE_CLUSTER_PING_SCHEDULE,
             RemoteClusterService.REMOTE_CLUSTER_COMPRESS,
+            SniffConnectionStrategy.REMOTE_CLUSTER_SEEDS_OLD,
+            SniffConnectionStrategy.REMOTE_CLUSTERS_PROXY,
+            SniffConnectionStrategy.REMOTE_CLUSTER_SEEDS,
+            SniffConnectionStrategy.REMOTE_NODE_CONNECTIONS,
             TransportCloseIndexAction.CLUSTER_INDICES_CLOSE_ENABLE_SETTING,
             ShardsLimitAllocationDecider.CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING,
             NodeConnectionsService.CLUSTER_NODE_RECONNECT_INTERVAL_SETTING,
@@ -521,7 +524,7 @@ public void apply(Settings value, Settings current, Settings previous) {
 
     public static List<SettingUpgrader<?>> BUILT_IN_SETTING_UPGRADERS = Collections.unmodifiableList(Arrays.asList(
             RemoteClusterAware.SEARCH_REMOTE_CLUSTER_SEEDS_UPGRADER,
-            RemoteClusterAware.SEARCH_REMOTE_CLUSTERS_PROXY_UPGRADER,
+            SniffConnectionStrategy.SEARCH_REMOTE_CLUSTERS_PROXY_UPGRADER,
             RemoteClusterService.SEARCH_REMOTE_CLUSTER_SKIP_UNAVAILABLE_UPGRADER));
 
 }