Elasticsearch作为分布式集群，客户端到服务端，节点与节点间通信有TCP和Http通信协议，底层实现为Netty框架。不了解Netty的同学先了解Netty基本原理及使用https://www.cnblogs.com/zhxdxf/articles/10340791.html。
1.关于启动
HTTP请求仅提供服务端响应，节点启动时启动HTTP服务端，TCP请求时ES的节点即作为服务端，又作为客户端，需要启动Transport的服务端、客户端服务。节点启动请参考ElasticSearch源码之启动类
injector.getInstance(HttpServerTransport.class).start();//提供HttpServerTransport服务的启动
最终调用Netty4HttpServerTransport中的doStart()方法
serverBootstrap = new ServerBootstrap();//即Netty的服务端启动方式
serverBootstrap.childHandler(configureServerChannelHandler());//添加服务端接消息的处理类
this.requestHandler = new Netty4HttpRequestHandler(transport, detailedErrorsEnabled, threadContext);
ch.pipeline().addLast("handler", requestHandler);
protected void doStart() { boolean success = false; try { this.serverOpenChannels = new Netty4OpenChannelsHandler(logger); serverBootstrap = new ServerBootstrap(); if (blockingServer) { serverBootstrap.group(new OioEventLoopGroup(workerCount, daemonThreadFactory(settings, HTTP_SERVER_WORKER_THREAD_NAME_PREFIX))); serverBootstrap.channel(OioServerSocketChannel.class); } else { serverBootstrap.group(new NioEventLoopGroup(workerCount, daemonThreadFactory(settings, HTTP_SERVER_WORKER_THREAD_NAME_PREFIX))); serverBootstrap.channel(NioServerSocketChannel.class); } serverBootstrap.childHandler(configureServerChannelHandler()); serverBootstrap.childOption(ChannelOption.TCP_NODELAY, SETTING_HTTP_TCP_NO_DELAY.get(settings)); serverBootstrap.childOption(ChannelOption.SO_KEEPALIVE, SETTING_HTTP_TCP_KEEP_ALIVE.get(settings)); final ByteSizeValue tcpSendBufferSize = SETTING_HTTP_TCP_SEND_BUFFER_SIZE.get(settings); if (tcpSendBufferSize.getBytes() > 0) { serverBootstrap.childOption(ChannelOption.SO_SNDBUF, Math.toIntExact(tcpSendBufferSize.getBytes())); } final ByteSizeValue tcpReceiveBufferSize = SETTING_HTTP_TCP_RECEIVE_BUFFER_SIZE.get(settings); if (tcpReceiveBufferSize.getBytes() > 0) { serverBootstrap.childOption(ChannelOption.SO_RCVBUF, Math.toIntExact(tcpReceiveBufferSize.getBytes())); } serverBootstrap.option(ChannelOption.RCVBUF_ALLOCATOR, recvByteBufAllocator); serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR, recvByteBufAllocator); final boolean reuseAddress = SETTING_HTTP_TCP_REUSE_ADDRESS.get(settings); serverBootstrap.option(ChannelOption.SO_REUSEADDR, reuseAddress); serverBootstrap.childOption(ChannelOption.SO_REUSEADDR, reuseAddress); this.boundAddress = createBoundHttpAddress(); if (logger.isInfoEnabled()) { logger.info("{}", boundAddress); } success = true; } finally { if (success == false) { doStop(); // otherwise we leak threads since we never moved to started } } }
TransportService transportService = injector.getInstance(TransportService.class);//提供Transport服务的启动
transportService.start();
最终调用Netty4Transport中的doStart()方法
bootstrap = createBootstrap();//客户端启动
bootstrap.handler(getClientChannelInitializer());//添加客户端消息处理类
ch.pipeline().addLast("dispatcher", new Netty4MessageChannelHandler(Netty4Transport.this, ".client"));
createServerBootstrap(entry.getKey(), settings);//服务端启动
serverBootstrap.childHandler(getServerChannelInitializer(name, settings));//添加服务端消息处理类
ch.pipeline().addLast("dispatcher", new Netty4MessageChannelHandler(Netty4Transport.this, name));
@Override protected void doStart() { boolean success = false; try { bootstrap = createBootstrap(); if (NetworkService.NETWORK_SERVER.get(settings)) { final Netty4OpenChannelsHandler openChannels = new Netty4OpenChannelsHandler(logger); this.serverOpenChannels = openChannels; // loop through all profiles and start them up, special handling for default one for (Map.Entry<String, Settings> entry : buildProfileSettings().entrySet()) { // merge fallback settings with default settings with profile settings so we have complete settings with default values final Settings settings = Settings.builder() .put(createFallbackSettings()) .put(entry.getValue()).build(); createServerBootstrap(entry.getKey(), settings); bindServer(entry.getKey(), settings); } } super.doStart(); success = true; } finally { if (success == false) { doStop(); } } }
当客户端发送消息时，建立连接。（调用过程见下一小节）
@Override public void connectToNode(DiscoveryNode node, ConnectionProfile connectionProfile, CheckedBiConsumer<Connection, ConnectionProfile, IOException> connectionValidator) throws ConnectTransportException { connectionProfile = resolveConnectionProfile(connectionProfile, defaultConnectionProfile); if (node == null) { throw new ConnectTransportException(null, "can't connect to a null node"); } globalLock.readLock().lock(); // ensure we don't open connections while we are closing try { ensureOpen(); try (Releasable ignored = connectionLock.acquire(node.getId())) { NodeChannels nodeChannels = connectedNodes.get(node); if (nodeChannels != null) { return; } boolean success = false; try { nodeChannels = openConnection(node, connectionProfile); connectionValidator.accept(nodeChannels, connectionProfile); // we acquire a connection lock, so no way there is an existing connection connectedNodes.put(node, nodeChannels); if (logger.isDebugEnabled()) { logger.debug("connected to node [{}]", node); } transportServiceAdapter.onNodeConnected(node); success = true; } catch (ConnectTransportException e) { throw e; } catch (Exception e) { throw new ConnectTransportException(node, "general node connection failure", e); } finally { if (success == false) { // close the connection if there is a failure logger.trace( (Supplier<?>) () -> new ParameterizedMessage( "failed to connect to [{}], cleaning dangling connections", node)); IOUtils.closeWhileHandlingException(nodeChannels); } } } } finally { globalLock.readLock().unlock(); } }
Netty4HttpServerTransport类图 Netty4ServerTransport类图
2.客户端发送请求
客户端类图
发送请求后，执行客户端的execute()方法到doExecute()方法
@Override protected <Request extends ActionRequest, Response extends ActionResponse, RequestBuilder extends ActionRequestBuilder<Request, Response, RequestBuilder>> void doExecute(Action<Request, Response, RequestBuilder> action, Request request, ActionListener<Response> listener) { proxy.execute(action, request, listener); }
final TransportActionNodeProxy<Request, Response> proxy = proxies.get(action);//根据action类型不同，生产执行不同的execute方法 nodesService.execute((n, l) -> proxy.execute(n, request, l), listener);
transportService.sendRequest(node, action.name(), request, transportOptions, new ActionListenerResponseHandler<>(listener, action::newResponse)); }
Transport.Connection connection = getConnection(node);//节点连接
sendRequest(connection, action, request, options, handler);//发送请求
connection.sendRequest(requestId, action, request, options);
通过channel发送请求
Channel channel = channel(options.type());
sendRequestToChannel(this.node, channel, requestId, action, request, options, getVersion(), (byte)0);
最终执行Netty4Transport的sendMessage方法将请求发送至channel
@Override protected void sendMessage(Channel channel, BytesReference reference, Runnable sendListener) { final ChannelFuture future = channel.writeAndFlush(Netty4Utils.toByteBuf(reference)); future.addListener(f -> sendListener.run()); }
3.服务端处理请求
服务端通过Netty4HttpRequestHandler的channelRead得到客户端请求，通过MessageReceived接受并处理请求
transport.messageReceived(reference, ctx.channel(), profileName, remoteAddress, remainingMessageSize);
final RequestHandlerRegistry reg = transportServiceAdapter.getRequestHandler(action);//根据action类型，生产具体的TransportRequest子类
final TransportRequest request = reg.newRequest();
threadPool.executor(reg.getExecutor()).execute(new RequestHandler(reg, request, transportChannel));
@Override protected void doRun() throws Exception { reg.processMessageReceived(request, transportChannel);// }
handler.messageReceived(request, channel);//TransportRequestHandler中的messageReceived方法
最终调用TransportHandler中的messageReceived方法 public final void messageReceived(final Request request, final TransportChannel channel, Task task) throws Exception { // We already got the task created on the network layer - no need to create it again on the transport layer execute(task, request, new ActionListener<Response>() {//执行具体的请求处理 @Override public void onResponse(Response response) { try { channel.sendResponse(response); } catch (Exception e) { onFailure(e); } } .......
4.示例bulk请求API
transportClient.bulk(bulkRequest);
依次执行：
public ActionFuture<BulkResponse> bulk(final BulkRequest request) { return execute(BulkAction.INSTANCE, request); }
final TransportActionNodeProxy<Request, Response> proxy = proxies.get(action);//proxy则根据不同的action，生成不同的TransportActionNodeProxy
nodesService.execute((n, l) -> proxy.execute(n, request, l), listener);//nodesService为TransportClientNodesService实例
public <Response> void execute(NodeListenerCallback<Response> callback, ActionListener<Response> listener) { // we first read nodes before checking the closed state; this // is because otherwise we could be subject to a race where we // read the state as not being closed, and then the client is // closed and the nodes list is cleared, and then a // NoNodeAvailableException is thrown // it is important that the order of first setting the state of // closed and then clearing the list of nodes is maintained in // the close method final List<DiscoveryNode> nodes = this.nodes; if (closed) { throw new IllegalStateException("transport client is closed"); } ensureNodesAreAvailable(nodes); int index = getNodeNumber(); RetryListener<Response> retryListener = new RetryListener<>(callback, listener, nodes, index, hostFailureListener); DiscoveryNode node = retryListener.getNode(0); try { callback.doWithNode(node, retryListener); } catch (Exception e) { try { //this exception can't come from the TransportService as it doesn't throw exception at all listener.onFailure(e); } finally { retryListener.maybeNodeFailed(node, e); } } }
final DiscoveryNode getNode(int i) { return nodes.get((index + i) % nodes.size()); }
public void execute(final DiscoveryNode node, final Request request, final ActionListener<Response> listener) { ActionRequestValidationException validationException = request.validate(); if (validationException != null) { listener.onFailure(validationException); return; } transportService.sendRequest(node, action.name(), request, transportOptions, new ActionListenerResponseHandler<>(listener, action::newResponse));//根据请求类型调用sendRequest方法 }
public final <T extends TransportResponse> void sendRequest(final DiscoveryNode node, final String action, final TransportRequest request, final TransportRequestOptions options, TransportResponseHandler<T> handler) { try { Transport.Connection connection = getConnection(node);//连接节点 sendRequest(connection, action, request, options, handler);//处理请求 } catch (NodeNotConnectedException ex) { // the caller might not handle this so we invoke the handler handler.handleException(ex); } }
@Override public void sendRequest(long requestId, String action, TransportRequest request, TransportRequestOptions options) throws IOException, TransportException { if (closed.get()) { throw new NodeNotConnectedException(node, "connection already closed"); } Channel channel = channel(options.type());//根据不同的请求类型，添加不同的过滤器 sendRequestToChannel(this.node, channel, requestId, action, request, options, getVersion(), (byte)0); } }
private boolean internalSendMessage(Channel targetChannel, BytesReference message, Runnable onRequestSent) throws IOException { boolean success; try { sendMessage(targetChannel, message, onRequestSent);//终极调用Netty4Transport的sendMessage方法 success = true; } catch (IOException ex) { // passing exception handling to deal with this and raise disconnect events and decide the right logging level onException(targetChannel, ex); success = false; } return success; }
@Override protected void sendMessage(Channel channel, BytesReference reference, Runnable sendListener) { final ChannelFuture future = channel.writeAndFlush(Netty4Utils.toByteBuf(reference));//向服务端发送消息 future.addListener(f -> sendListener.run());