网关Spring Cloud Gateway

概述

spring cloud gateway提供了一个构建在 Spring 生态系统之上的 API 网关，包括：Spring 5、Spring Boot 2 和 Project Reactor。 Spring Cloud Gateway 旨在提供一种简单而有效的方式来路由到 API 并为它们提供交叉关注点，例如：安全性、监控/指标和弹性。

• Route: The basic building block of the gateway. It is defined by an ID, a destination URI, a collection of predicates, and a collection of filters. A route is matched if the aggregate predicate is true.
• Predicate: This is a Java 8 Function Predicate. The input type is a Spring Framework ServerWebExchange. This lets you match on anything from the HTTP request, such as headers or parameters.
• Filter: These are instances of GatewayFilter that have been constructed with a specific factory. Here, you can modify requests and responses before or after sending the downstream request.

spring_cloud_gateway_diagram.png

依赖的框架以及版本

工具	版本
spring-boot	2.5.0
spring-cloud	2020.0.1
Spring Cloud Alibaba	2021.1
nacos	2.0.3

实现步骤

1，spring cloud gateway与nacos集成两步~

• 添加依赖

  <properties>
     <java.version>1.8</java.version>
     <spring-cloud.version>2020.0.1</spring-cloud.version>
     <spring-cloud-alibaba.version>2021.1</spring-cloud-alibaba.version>
  </properties>
  <dependencies>
     <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-webflux</artifactId>
     </dependency>
     <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-gateway</artifactId>
     </dependency>
     <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
     </dependency>
     <dependency>
        <groupId>com.alibaba.cloud</groupId>
        <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
     </dependency>
     <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-loadbalancer</artifactId>
     </dependency>
  </dependencies>
  <dependencyManagement>
     <dependencies>
        <dependency>
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-dependencies</artifactId>
           <version>${spring-cloud.version}</version>
           <type>pom</type>
           <scope>import</scope>
        </dependency>
        <dependency>
           <groupId>com.alibaba.cloud</groupId>
           <artifactId>spring-cloud-alibaba-dependencies</artifactId>
           <version>${spring-cloud-alibaba.version}</version>
           <type>pom</type>
           <scope>import</scope>
        </dependency>
     </dependencies>
  </dependencyManagement>
  

• 配置application.yml文件，无需配置到bootstrap.yml文件中了，新版本nacos配置会报错。

  spring:
    application:
      name: gateway
    cloud:
      gateway:
        discovery:
          locator:
            enabled: true
            lower-case-service-id: true
  #      routes:
  #        - id: header_route
  #          uri: lb://archetype
  #          predicates:
  #            - Header=X-Request-Id, \d+
      nacos:
        discovery:
          server-addr: 127.0.0.1:8848
          namespace: lqd
          password: nacos
          username: nacos
  

• Postman验证：

  image-20210817094935112.png

2，了解下Route、Predicates、Filter

• Route、Predicates 验证：Route Predicate Factories The Header Route Predicate Factory 请求头过滤添加如下配置，通过Postman请求验证

  routes:
    - id: header_route
      uri: lb://archetype
      predicates:
        - Header=X-Request-Id, \d+
  

  image-20210817095807823.png image-20210817095846592.png

• Filter验证The AddResponseHeader GatewayFilter Factory

  routes:
    - id: header_route
      uri: lb://archetype
      predicates:
        - Header=X-Request-Id, \d+
      filters:
        - AddResponseHeader=X-Response-TIME, 20210817
  

  image-20210817103422397.png

关键源码

Predicate的核心类RoutePredicateHandlerMapping、AbstractRoutePredicateFactory

• RoutePredicateHandlerMapping

  protected Mono<Route> lookupRoute(ServerWebExchange exchange) {
     return this.routeLocator.getRoutes()
           // individually filter routes so that filterWhen error delaying is not a
           // problem
           .concatMap(route -> Mono.just(route).filterWhen(r -> {
              // add the current route we are testing
              exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());
              return r.getPredicate().apply(exchange);
           })
                 // instead of immediately stopping main flux due to error, log and
                 // swallow it
                 .doOnError(e -> logger.error("Error applying predicate for route: " + route.getId(), e))
                 .onErrorResume(e -> Mono.empty()))
           // .defaultIfEmpty() put a static Route not found
           // or .switchIfEmpty()
           // .switchIfEmpty(Mono.<Route>empty().log("noroute"))
           .next()
           // TODO: error handling
           .map(route -> {
              if (logger.isDebugEnabled()) {
                 logger.debug("Route matched: " + route.getId());
              }
              validateRoute(route, exchange);
              return route;
           });
  
     /*
      * TODO: trace logging if (logger.isTraceEnabled()) {
      * logger.trace("RouteDefinition did not match: " + routeDefinition.getId()); }
      */
  }
  

Filter核心类DefaultGatewayFilterChain、核心接口GlobalFilter、代理请求转发类NettyRoutingFilter

• DefaultGatewayFilterChain这个类可以看到springCloud的Filter的责任链。

@Override
public Mono<Void> 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
      }
   });
}

例如：RouteToRequestUrlFilter通过这个类可以方便查看到路由后的访问路径。

• NettyRoutingFilter这个类是gateway转发服务到代理服务的处理类

  public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
     URI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);
  
     String scheme = requestUrl.getScheme();
     if (isAlreadyRouted(exchange) || (!"http".equals(scheme) && !"https".equals(scheme))) {
        return chain.filter(exchange);
     }
     setAlreadyRouted(exchange);
  
     ServerHttpRequest request = exchange.getRequest();
  
     final HttpMethod method = HttpMethod.valueOf(request.getMethodValue());
     final String url = requestUrl.toASCIIString();
  
     HttpHeaders filtered = filterRequest(getHeadersFilters(), exchange);
  
     final DefaultHttpHeaders httpHeaders = new DefaultHttpHeaders();
     filtered.forEach(httpHeaders::set);
  
     boolean preserveHost = exchange.getAttributeOrDefault(PRESERVE_HOST_HEADER_ATTRIBUTE, false);
     Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);
  
     Flux<HttpClientResponse> responseFlux = getHttpClient(route, exchange).headers(headers -> {
        headers.add(httpHeaders);
        // Will either be set below, or later by Netty
        headers.remove(HttpHeaders.HOST);
        if (preserveHost) {
           String host = request.getHeaders().getFirst(HttpHeaders.HOST);
           headers.add(HttpHeaders.HOST, host);
        }
     }).request(method).uri(url).send((req, nettyOutbound) -> {
        if (log.isTraceEnabled()) {
           nettyOutbound.withConnection(connection -> log.trace("outbound route: "
                 + connection.channel().id().asShortText() + ", inbound: " + exchange.getLogPrefix()));
        }
        return nettyOutbound.send(request.getBody().map(this::getByteBuf));
     }).responseConnection((res, connection) -> {
  ......
  
     return responseFlux.then(chain.filter(exchange));
  }
  

异常报错

1，出现503 Service Unavailable

解决方法：增加spring-cloud-starter-loadbalancer依赖

<dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-loadbalancer</artifactId>
</dependency>

参考

spring cloud 与 spring cloud alibaba 版本对应关系
spring cloud gateway
Reactor 3
Spring 5 WebFlux
例子