The http module allows to expose Elasticsearch APIs over HTTP.The http mechanism is completely asynchronous in nature, meaning that there is no blocking thread waiting for a response. The benefit of using asynchronous communication for HTTP is solving the C10k problem.When possible, consider using HTTP keep alive when connecting for better performance and try to get your favorite client not to do HTTP chunking.

public final class HttpTransportSettings {public static final Setting<Boolean> SETTING_CORS_ENABLED =Setting.boolSetting("http.cors.enabled", false, Property.NodeScope);public static final Setting<String> SETTING_CORS_ALLOW_ORIGIN =new Setting<>("http.cors.allow-origin", "", (value) -> value, Property.NodeScope);public static final Setting<Integer> SETTING_CORS_MAX_AGE =Setting.intSetting("http.cors.max-age", 1728000, Property.NodeScope);public static final Setting<String> SETTING_CORS_ALLOW_METHODS =new Setting<>("http.cors.allow-methods", "OPTIONS,HEAD,GET,POST,PUT,DELETE", (value) -> value, Property.NodeScope);public static final Setting<String> SETTING_CORS_ALLOW_HEADERS =new Setting<>("http.cors.allow-headers", "X-Requested-With,Content-Type,Content-Length", (value) -> value, Property.NodeScope);public static final Setting<Boolean> SETTING_CORS_ALLOW_CREDENTIALS =Setting.boolSetting("http.cors.allow-credentials", false, Property.NodeScope);public static final Setting<Integer> SETTING_PIPELINING_MAX_EVENTS =Setting.intSetting("http.pipelining.max_events", 10000, Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_COMPRESSION =Setting.boolSetting("http.compression", true, Property.NodeScope);// we intentionally use a different compression level as Netty here as our benchmarks have shown that a compression level of 3 is the// best compromise between reduction in network traffic and added latency. For more details please check #7309.public static final Setting<Integer> SETTING_HTTP_COMPRESSION_LEVEL =Setting.intSetting("http.compression_level", 3, Property.NodeScope);public static final Setting<List<String>> SETTING_HTTP_HOST =listSetting("http.host", emptyList(), Function.identity(), Property.NodeScope);public static final Setting<List<String>> SETTING_HTTP_PUBLISH_HOST =listSetting("http.publish_host", SETTING_HTTP_HOST, Function.identity(), Property.NodeScope);public static final Setting<List<String>> SETTING_HTTP_BIND_HOST =listSetting("http.bind_host", SETTING_HTTP_HOST, Function.identity(), Property.NodeScope);public static final Setting<PortsRange> SETTING_HTTP_PORT =new Setting<>("http.port", "9200-9300", PortsRange::new, Property.NodeScope);public static final Setting<Integer> SETTING_HTTP_PUBLISH_PORT =Setting.intSetting("http.publish_port", -1, -1, Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_DETAILED_ERRORS_ENABLED =Setting.boolSetting("http.detailed_errors.enabled", true, Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_CONTENT_TYPE_REQUIRED =new Setting<>("http.content_type.required", (s) -> Boolean.toString(true), (s) -> {final boolean value = Booleans.parseBoolean(s);if (value == false) {throw new IllegalArgumentException("http.content_type.required cannot be set to false. It exists only to make a rolling" +" upgrade easier");}return true;}, Property.NodeScope, Property.Deprecated);public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_CONTENT_LENGTH =Setting.byteSizeSetting("http.max_content_length",new ByteSizeValue(100, ByteSizeUnit.MB),new ByteSizeValue(0, ByteSizeUnit.BYTES),new ByteSizeValue(Integer.MAX_VALUE, ByteSizeUnit.BYTES),Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_CHUNK_SIZE =Setting.byteSizeSetting("http.max_chunk_size", new ByteSizeValue(8, ByteSizeUnit.KB), Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_HEADER_SIZE =Setting.byteSizeSetting("http.max_header_size", new ByteSizeValue(8, ByteSizeUnit.KB), Property.NodeScope);public static final Setting<Integer> SETTING_HTTP_MAX_WARNING_HEADER_COUNT =Setting.intSetting("http.max_warning_header_count", -1, -1, Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_WARNING_HEADER_SIZE =Setting.byteSizeSetting("http.max_warning_header_size", new ByteSizeValue(-1), Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_MAX_INITIAL_LINE_LENGTH =Setting.byteSizeSetting("http.max_initial_line_length", new ByteSizeValue(4, ByteSizeUnit.KB), Property.NodeScope);// don't reset cookies by default, since I don't think we really need to// note, parsing cookies was fixed in netty 3.5.1 regarding stack allocation, but still, currently, we don't need cookiespublic static final Setting<Boolean> SETTING_HTTP_RESET_COOKIES =Setting.boolSetting("http.reset_cookies", false, Property.NodeScope);// A default of 0 means that by default there is no read timeoutpublic static final Setting<TimeValue> SETTING_HTTP_READ_TIMEOUT =Setting.timeSetting("http.read_timeout", new TimeValue(0), new TimeValue(0), Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_TCP_NO_DELAY =boolSetting("http.tcp_no_delay", NetworkService.TCP_NO_DELAY, Setting.Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_TCP_KEEP_ALIVE =boolSetting("http.tcp.keep_alive", NetworkService.TCP_KEEP_ALIVE, Setting.Property.NodeScope);public static final Setting<Boolean> SETTING_HTTP_TCP_REUSE_ADDRESS =boolSetting("http.tcp.reuse_address", NetworkService.TCP_REUSE_ADDRESS, Setting.Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_TCP_SEND_BUFFER_SIZE =Setting.byteSizeSetting("http.tcp.send_buffer_size", NetworkService.TCP_SEND_BUFFER_SIZE, Setting.Property.NodeScope);public static final Setting<ByteSizeValue> SETTING_HTTP_TCP_RECEIVE_BUFFER_SIZE =Setting.byteSizeSetting("http.tcp.receive_buffer_size", NetworkService.TCP_RECEIVE_BUFFER_SIZE, Setting.Property.NodeScope);private HttpTransportSettings() {}
}

protected void bindServer() {// Bind and start to accept incoming connections.
        InetAddress hostAddresses[];try {hostAddresses = networkService.resolveBindHostAddresses(bindHosts);} catch (IOException e) {throw new BindHttpException("Failed to resolve host [" + Arrays.toString(bindHosts) + "]", e);}List<TransportAddress> boundAddresses = new ArrayList<>(hostAddresses.length);for (InetAddress address : hostAddresses) {boundAddresses.add(bindAddress(address));}final InetAddress publishInetAddress;try {publishInetAddress = networkService.resolvePublishHostAddresses(publishHosts);} catch (Exception e) {throw new BindTransportException("Failed to resolve publish address", e);}final int publishPort = resolvePublishPort(settings, boundAddresses, publishInetAddress);TransportAddress publishAddress = new TransportAddress(new InetSocketAddress(publishInetAddress, publishPort));this.boundAddress = new BoundTransportAddress(boundAddresses.toArray(new TransportAddress[0]), publishAddress);logger.info("{}", boundAddress);}

@Overridepublic void dispatchRequest(RestRequest request, RestChannel channel, ThreadContext threadContext) {if (request.rawPath().equals("/favicon.ico")) {handleFavicon(request, channel);return;}try {tryAllHandlers(request, channel, threadContext);} catch (Exception e) {try {channel.sendResponse(new BytesRestResponse(channel, e));} catch (Exception inner) {inner.addSuppressed(e);logger.error(() ->new ParameterizedMessage("failed to send failure response for uri [{}]", request.uri()), inner);}}}

    @Overridepublic final void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {// prepare the request for execution; has the side effect of touching the request parametersfinal RestChannelConsumer action = prepareRequest(request, client);// validate unconsumed params, but we must exclude params used to format the response// use a sorted set so the unconsumed parameters appear in a reliable sorted orderfinal SortedSet<String> unconsumedParams =request.unconsumedParams().stream().filter(p -> !responseParams().contains(p)).collect(Collectors.toCollection(TreeSet::new));// validate the non-response paramsif (!unconsumedParams.isEmpty()) {final Set<String> candidateParams = new HashSet<>();candidateParams.addAll(request.consumedParams());candidateParams.addAll(responseParams());throw new IllegalArgumentException(unrecognized(request, unconsumedParams, candidateParams, "parameter"));}usageCount.increment();// execute the action
        action.accept(channel);}

The transport module is used for internal communication between nodes within the cluster. Each call that goes from one node to the other uses the transport module (for example, when an HTTP GET request is processed by one node, and should actually be processed by another node that holds the data).The transport mechanism is completely asynchronous in nature, meaning that there is no blocking thread waiting for a response. The benefit of using asynchronous communication is first solving the C10k problem, as well as being the ideal solution for scatter (broadcast) / gather operations such as search in Elasticsearch.

 public static final String TRANSPORT_SERVER_WORKER_THREAD_NAME_PREFIX = "transport_server_worker";public static final String TRANSPORT_CLIENT_BOSS_THREAD_NAME_PREFIX = "transport_client_boss";public static final Setting<List<String>> HOST =listSetting("transport.host", emptyList(), Function.identity(), Setting.Property.NodeScope);public static final Setting<List<String>> BIND_HOST =listSetting("transport.bind_host", HOST, Function.identity(), Setting.Property.NodeScope);public static final Setting<List<String>> PUBLISH_HOST =listSetting("transport.publish_host", HOST, Function.identity(), Setting.Property.NodeScope);public static final Setting<String> PORT =new Setting<>("transport.tcp.port", "9300-9400", Function.identity(), Setting.Property.NodeScope);public static final Setting<Integer> PUBLISH_PORT =intSetting("transport.publish_port", -1, -1, Setting.Property.NodeScope);public static final String DEFAULT_PROFILE = "default";// the scheduled internal ping interval setting, defaults to disabled (-1)public static final Setting<TimeValue> PING_SCHEDULE =timeSetting("transport.ping_schedule", TimeValue.timeValueSeconds(-1), Setting.Property.NodeScope);public static final Setting<Boolean> TCP_NO_DELAY =boolSetting("transport.tcp_no_delay", NetworkService.TCP_NO_DELAY, Setting.Property.NodeScope);public static final Setting<Boolean> TCP_KEEP_ALIVE =boolSetting("transport.tcp.keep_alive", NetworkService.TCP_KEEP_ALIVE, Setting.Property.NodeScope);public static final Setting<Boolean> TCP_REUSE_ADDRESS =boolSetting("transport.tcp.reuse_address", NetworkService.TCP_REUSE_ADDRESS, Setting.Property.NodeScope);public static final Setting<ByteSizeValue> TCP_SEND_BUFFER_SIZE =Setting.byteSizeSetting("transport.tcp.send_buffer_size", NetworkService.TCP_SEND_BUFFER_SIZE, Setting.Property.NodeScope);public static final Setting<ByteSizeValue> TCP_RECEIVE_BUFFER_SIZE =Setting.byteSizeSetting("transport.tcp.receive_buffer_size", NetworkService.TCP_RECEIVE_BUFFER_SIZE, Setting.Property.NodeScope);public static final Setting.AffixSetting<Boolean> TCP_NO_DELAY_PROFILE = affixKeySetting("transport.profiles.", "tcp_no_delay",key -> boolSetting(key, TcpTransport.TCP_NO_DELAY, Setting.Property.NodeScope));public static final Setting.AffixSetting<Boolean> TCP_KEEP_ALIVE_PROFILE = affixKeySetting("transport.profiles.", "tcp_keep_alive",key -> boolSetting(key, TcpTransport.TCP_KEEP_ALIVE, Setting.Property.NodeScope));public static final Setting.AffixSetting<Boolean> TCP_REUSE_ADDRESS_PROFILE = affixKeySetting("transport.profiles.", "reuse_address",key -> boolSetting(key, TcpTransport.TCP_REUSE_ADDRESS, Setting.Property.NodeScope));public static final Setting.AffixSetting<ByteSizeValue> TCP_SEND_BUFFER_SIZE_PROFILE = affixKeySetting("transport.profiles.","send_buffer_size", key -> Setting.byteSizeSetting(key, TcpTransport.TCP_SEND_BUFFER_SIZE, Setting.Property.NodeScope));public static final Setting.AffixSetting<ByteSizeValue> TCP_RECEIVE_BUFFER_SIZE_PROFILE = affixKeySetting("transport.profiles.","receive_buffer_size", key -> Setting.byteSizeSetting(key, TcpTransport.TCP_RECEIVE_BUFFER_SIZE, Setting.Property.NodeScope));public static final Setting.AffixSetting<List<String>> BIND_HOST_PROFILE = affixKeySetting("transport.profiles.", "bind_host",key -> listSetting(key, BIND_HOST, Function.identity(), Setting.Property.NodeScope));public static final Setting.AffixSetting<List<String>> PUBLISH_HOST_PROFILE = affixKeySetting("transport.profiles.", "publish_host",key -> listSetting(key, PUBLISH_HOST, Function.identity(), Setting.Property.NodeScope));public static final Setting.AffixSetting<String> PORT_PROFILE = affixKeySetting("transport.profiles.", "port",key -> new Setting<>(key, PORT, Function.identity(), Setting.Property.NodeScope));public static final Setting.AffixSetting<Integer> PUBLISH_PORT_PROFILE = affixKeySetting("transport.profiles.", "publish_port",key -> intSetting(key, -1, -1, Setting.Property.NodeScope));

    @Overrideprotected void doStart() {boolean success = false;try {clientBootstrap = createClientBootstrap();if (NetworkService.NETWORK_SERVER.get(settings)) {for (ProfileSettings profileSettings : profileSettings) {createServerBootstrap(profileSettings);bindServer(profileSettings);}}super.doStart();success = true;} finally {if (success == false) {doStop();}}}

    @Overrideprotected void doStart() {transport.addMessageListener(this);connectionManager.addListener(this);transport.start();if (transport.boundAddress() != null && logger.isInfoEnabled()) {logger.info("{}", transport.boundAddress());for (Map.Entry<String, BoundTransportAddress> entry : transport.profileBoundAddresses().entrySet()) {logger.info("profile [{}]: {}", entry.getKey(), entry.getValue());}}localNode = localNodeFactory.apply(transport.boundAddress());if (connectToRemoteCluster) {// here we start to connect to the remote clusters
            remoteClusterService.initializeRemoteClusters();}}

    /*** Creates a new TransportClient with the given settings and plugins*/public TransportClient(Settings settings, Collection<Class<? extends Plugin>> plugins) {this(buildTemplate(settings, Settings.EMPTY, plugins, null));}private static ClientTemplate buildTemplate(Settings providedSettings, Settings defaultSettings,Collection<Class<? extends Plugin>> plugins, HostFailureListener failureListner) {if (Node.NODE_NAME_SETTING.exists(providedSettings) == false) {providedSettings = Settings.builder().put(providedSettings).put(Node.NODE_NAME_SETTING.getKey(), "_client_").build();}final PluginsService pluginsService = newPluginService(providedSettings, plugins);final Settings settings =Settings.builder().put(defaultSettings).put(pluginsService.updatedSettings()).put(TcpTransport.FEATURE_PREFIX + "." + TRANSPORT_CLIENT_FEATURE, true).build();final List<Closeable> resourcesToClose = new ArrayList<>();final ThreadPool threadPool = new ThreadPool(settings);resourcesToClose.add(() -> ThreadPool.terminate(threadPool, 10, TimeUnit.SECONDS));final NetworkService networkService = new NetworkService(Collections.emptyList());try {final List<Setting<?>> additionalSettings = new ArrayList<>(pluginsService.getPluginSettings());final List<String> additionalSettingsFilter = new ArrayList<>(pluginsService.getPluginSettingsFilter());for (final ExecutorBuilder<?> builder : threadPool.builders()) {additionalSettings.addAll(builder.getRegisteredSettings());}SettingsModule settingsModule =new SettingsModule(settings, additionalSettings, additionalSettingsFilter, Collections.emptySet());SearchModule searchModule = new SearchModule(settings, true, pluginsService.filterPlugins(SearchPlugin.class));IndicesModule indicesModule = new IndicesModule(Collections.emptyList());List<NamedWriteableRegistry.Entry> entries = new ArrayList<>();entries.addAll(NetworkModule.getNamedWriteables());entries.addAll(searchModule.getNamedWriteables());entries.addAll(indicesModule.getNamedWriteables());entries.addAll(ClusterModule.getNamedWriteables());entries.addAll(pluginsService.filterPlugins(Plugin.class).stream().flatMap(p -> p.getNamedWriteables().stream()).collect(Collectors.toList()));NamedWriteableRegistry namedWriteableRegistry = new NamedWriteableRegistry(entries);NamedXContentRegistry xContentRegistry = new NamedXContentRegistry(Stream.of(searchModule.getNamedXContents().stream(),pluginsService.filterPlugins(Plugin.class).stream().flatMap(p -> p.getNamedXContent().stream())).flatMap(Function.identity()).collect(toList()));ModulesBuilder modules = new ModulesBuilder();// plugin modules must be added here, before others or we can get crazy injection errors...for (Module pluginModule : pluginsService.createGuiceModules()) {modules.add(pluginModule);}modules.add(b -> b.bind(ThreadPool.class).toInstance(threadPool));ActionModule actionModule = new ActionModule(true, settings, null, settingsModule.getIndexScopedSettings(),settingsModule.getClusterSettings(), settingsModule.getSettingsFilter(), threadPool,pluginsService.filterPlugins(ActionPlugin.class), null, null, null);modules.add(actionModule);CircuitBreakerService circuitBreakerService = Node.createCircuitBreakerService(settingsModule.getSettings(),settingsModule.getClusterSettings());resourcesToClose.add(circuitBreakerService);PageCacheRecycler pageCacheRecycler = new PageCacheRecycler(settings);BigArrays bigArrays = new BigArrays(pageCacheRecycler, circuitBreakerService);resourcesToClose.add(bigArrays);modules.add(settingsModule);NetworkModule networkModule = new NetworkModule(settings, true, pluginsService.filterPlugins(NetworkPlugin.class), threadPool,bigArrays, pageCacheRecycler, circuitBreakerService, namedWriteableRegistry, xContentRegistry, networkService, null);final Transport transport = networkModule.getTransportSupplier().get();final TransportService transportService = new TransportService(settings, transport, threadPool,networkModule.getTransportInterceptor(),boundTransportAddress -> DiscoveryNode.createLocal(settings, new TransportAddress(TransportAddress.META_ADDRESS, 0),UUIDs.randomBase64UUID()), null, Collections.emptySet());modules.add((b -> {b.bind(BigArrays.class).toInstance(bigArrays);b.bind(PluginsService.class).toInstance(pluginsService);b.bind(CircuitBreakerService.class).toInstance(circuitBreakerService);b.bind(NamedWriteableRegistry.class).toInstance(namedWriteableRegistry);b.bind(Transport.class).toInstance(transport);b.bind(TransportService.class).toInstance(transportService);b.bind(NetworkService.class).toInstance(networkService);}));Injector injector = modules.createInjector();final TransportClientNodesService nodesService =new TransportClientNodesService(settings, transportService, threadPool, failureListner == null? (t, e) -> {} : failureListner);// construct the list of client actionsfinal List<ActionPlugin> actionPlugins = pluginsService.filterPlugins(ActionPlugin.class);final List<Action> clientActions =actionPlugins.stream().flatMap(p -> p.getClientActions().stream()).collect(Collectors.toList());// add all the base actionsfinal List<? extends Action<?>> baseActions =actionModule.getActions().values().stream().map(ActionPlugin.ActionHandler::getAction).collect(Collectors.toList());clientActions.addAll(baseActions);final TransportProxyClient proxy = new TransportProxyClient(settings, transportService, nodesService, clientActions);List<LifecycleComponent> pluginLifecycleComponents = new ArrayList<>(pluginsService.getGuiceServiceClasses().stream().map(injector::getInstance).collect(Collectors.toList()));resourcesToClose.addAll(pluginLifecycleComponents);transportService.start();transportService.acceptIncomingRequests();ClientTemplate transportClient = new ClientTemplate(injector, pluginLifecycleComponents, nodesService, proxy,namedWriteableRegistry);resourcesToClose.clear();return transportClient;} finally {IOUtils.closeWhileHandlingException(resourcesToClose);}}