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This article shows you how to carry out SpringCloud Gateway full-link implementation analysis, the content is concise and easy to understand, absolutely can make your eyes bright, through the detailed introduction of this article, I hope you can get something.

1. Background

With the popularity of micro-service architecture, services are split according to different dimensions, and multiple services are often involved in one request. Many services may be distributed on thousands of servers, spanning many different data centers. In order to quickly locate and solve the fault, the application performance is analyzed, and the full-link monitoring component is produced under the background of this problem. The most famous is the Google Dapper mentioned in Google's public paper. To understand the behavior of distributed systems in this context, you need to monitor the associated actions across different applications and different servers.

1.1 full link principle

The call chain ID is added and transferred in the process of business call to generate link data between applications, and finally concatenate into a complete call chain. Each request has to pass through TxId, SpanId, and pSpanId throughout the call.

1.2 Spring Cloud Gateway

As the second generation gateway framework officially launched by Spring Cloud, Spring cloud gateway is a gateway developed based on Spring 5.0, Spring Boot2.0 and Reactor technology, and uses NIO model for communication.

1.2.2 Mono and Flux

Mono represents an asynchronous sequence containing 0 or 1 elements, that is, either the element was published successfully or an error occurred.

Flux and Mono can be converted to each other, such as counting a Flux sequence, the result is a Mono object, or combining two Mono sequences together, the result is a Flux object.

2. Spring Cloud Gateway does not do monitoring.

As an ingress gateway, Spring Cloud Gateway is mainly responsible for routing and forwarding services. If the gateway is not monitored, the whole link will lose the gateway node, which will be directly displayed for the user to access the subsequent application; it can not effectively locate whether the slow user request is the gateway problem or the follow-up node.

3.1.1 request entry for Spring Cloud Gateway

Org.springframework.http.server.reactive.ReactorHttpHandlerAdapter#apply first converts the received HttpServerRequest or the final HttpServerResponse wrapper that needs to be returned into ReactorServerHttpRequest and ReactorServerHttpResponse before processing the request.

Public Mono apply (HttpServerRequest request, HttpServerResponse response) {NettyDataBufferFactory bufferFactory = new NettyDataBufferFactory (response.alloc ()); ServerHttpRequest adaptedRequest;ServerHttpResponse adaptedResponse;try {adaptedRequest = new ReactorServerHttpRequest (request, bufferFactory); adaptedResponse = new ReactorServerHttpResponse (response, bufferFactory);} catch (URISyntaxException ex) {logger.error ("Invalid URL" >

3.1.2 construct gateway context

Org.springframework.web.server.adapter.HttpWebHandlerAdapter#handle

CreateExchange () constructs gateway context ServerWebExchange

GetDelegate () gets a series of WebHandler to be processed by delegating

Public Mono handle (ServerHttpRequest request, ServerHttpResponse response) {ServerWebExchange exchange = createExchange (request, response); return getDelegate (). Handle (exchange) .onErrorResume (ex-> handleFailure (request, response, ex)). Then (Mono.defer (response::setComplete));} protected ServerWebExchange createExchange (ServerHttpRequest request, ServerHttpResponse response) {return new DefaultServerWebExchange (request, response, this.sessionManager,getCodecConfigurer (), getLocaleContextResolver (), this.applicationContext);}

3.1.3 enter the Filter chain

Org.springframework.cloud.gateway.handler.FilteringWebHandler#handle gets the GatewayFilter array and creates a DefaultGatewayFilterChain based on the obtained GatewayFilter array to filter the request.

Public Mono handle (ServerWebExchange exchange) {Route route = exchange.getRequiredAttribute (GATEWAY_ROUTE_ATTR); List gatewayFilters = route.getFilters (); List combined = new ArrayList (this.globalFilters); combined.addAll (gatewayFilters); AnnotationAwareOrderComparator.sort (combined); logger.debug ("Sorted gatewayFilterFactories:" + combined); return new DefaultGatewayFilterChain (combined) .filter (exchange);}

3.1.4 execute Filter chain

Chained call of org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain#filter filter

Public Mono filter (ServerWebExchange exchange) {return Mono.defer (()-> {if (this.index)

< filters.size()) {GatewayFilter filter = filters.get(this.index);DefaultGatewayFilterChain chain = new DefaultGatewayFilterChain(this, this.index + 1);return filter.filter(exchange, chain);} else {return Mono.empty(); // complete}});} 3.1.5 Gateway Filter适配器 org.springframework.cloud.gateway.handler.FilteringWebHandler$GatewayFilterAdapter#filter GatewayFilterAdapter是GlobalFilter过滤器的包装类，最终委托Global Filter进行执行。 private static class GatewayFilterAdapter implements GatewayFilter { private final GlobalFilter delegate; public GatewayFilterAdapter(GlobalFilter delegate) { this.delegate = delegate; } public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) { return this.delegate.filter(exchange, chain); }} 3.1.6 Netty路由网关过滤器 org.springframework.cloud.gateway.filter.NettyRoutingFilter#filter GlobalFilter实现有很多，此处只分析NettyRoutingFIlter和NettyWriteResponseFilter。而NettyRoutingFilter负责使用 Netty HttpClient 代理对下游的请求。 public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) {// 获得 requestUrlURI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR); // 判断是否能够处理，http或https前缀String scheme = requestUrl.getScheme();if (isAlreadyRouted(exchange) || (!"http".equals(scheme) && !"https".equals(scheme))) {return chain.filter(exchange);}// 设置已经路由setAlreadyRouted(exchange); ServerHttpRequest request = exchange.getRequest();// 创建Netty Request Method对象final HttpMethod method = HttpMethod.valueOf(request.getMethod().toString());final String url = requestUrl.toString();HttpHeaders filtered = filterRequest(this.headersFilters.getIfAvailable(), exchange); final DefaultHttpHeaders httpHeaders = new DefaultHttpHeaders();filtered.forEach(httpHeaders::set); String transferEncoding = request.getHeaders().getFirst(HttpHeaders.TRANSFER_ENCODING);boolean chunkedTransfer = "chunked".equalsIgnoreCase(transferEncoding);boolean preserveHost = exchange.getAttributeOrDefault(PRESERVE_HOST_HEADER_ATTRIBUTE, false);// 请求后端服务return this.httpClient.request(method, url, req ->

{final HttpClientRequest proxyRequest = req.options (NettyPipeline.SendOptions::flushOnEach) .headers (httpHeaders) .chunkedTransfer (chunkedTransfer) .failOnServerError (false) .failOnClientError (false); if (preserveHost) {String host = request.getHeaders (). GetFirst (HttpHeaders.HOST); proxyRequest.header (HttpHeaders.HOST, host);} return proxyRequest.sendHeaders () / / send request header .send (request.getBody (). Map (dataBuffer-> / / send request Body ((NettyDataBuffer) dataBuffer). GetNativeBuffer () ) .doOnNext (res-> {ServerHttpResponse response = exchange.getResponse (); / / put headers and status so filters can modify the responseHttpHeaders headers = new HttpHeaders (); res.responseHeaders () .forEach (entry-> headers.add (entry.getKey (), entry.getValue (); exchange.getAttributes () .put ("original_response_content_type", headers.getContentType ()); HttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter (this.headersFilters.getIfAvailable (), headers, exchange, Type.RESPONSE); response.getHeaders (). PutAll (filteredResponseHeaders) HttpStatus status = HttpStatus.resolve (res.status (). Code ()); if (status! = null) {response.setStatusCode (status);} else if (response instanceof AbstractServerHttpResponse) {/ / https://jira.spring.io/browse/SPR-16748((AbstractServerHttpResponse) response) .setStatusCodeValue (res.status (). Code ());} else {throw new IllegalStateException ("Unable to set status code on response:" >

3.1.7 Netty writeback response Gateway filter

Org.springframework.cloud.gateway.filter.NettyWriteResponseFilter#filter NettyWriteResponseFilter appears in pairs with NettyRoutingFilter and is responsible for writing the proxy response back to the gateway client response.

Public Mono filter (ServerWebExchange exchange, GatewayFilterChain chain) {/ / then method implements After Filter logic return chain.filter (exchange). Then (Mono.defer (()-> {/ / get Netty ResponseHttpClientResponse clientResponse = exchange.getAttribute (CLIENT_RESPONSE_ATTR); if (clientResponse = = null) {return Mono.empty ();} log.trace ("NettyWriteResponseFilter start"); ServerHttpResponse response = exchange.getResponse (); / / write Netty Response back to client NettyDataBufferFactory factory = (NettyDataBufferFactory) response.bufferFactory () / / TODO: what if it's not nettyfinal Flux body = clientResponse.receive (). Retain () / ByteBufFlux = > ByteBufFlux.map (factory::wrap); / / ByteBufFlux = > Flux MediaType contentType = response.getHeaders (). GetContentType (); return (isStreamingMediaType (contentType)? response.writeAndFlushWith (body.map (Flux::just)): response.writeWith (body));} 4. Spring Cloud Gateway for monitoring

When the gateway is finally monitored, we can see the application request flow, the request service diversion of the gateway, and the call load of each application.

The above content is how to analyze the full-link implementation of SpringCloud Gateway. Have you learned the knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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