API 网关

API 网关出现的原因是微服务架构的出现，不同的微服务一般会有不同的网络地址，而外部客户端可能需要调用多个服务的接口才能完成一个业务需求，如果让客户端直接与各个微服务通信，会有以下的问题：

1. 客户端会多次请求不同的微服务，增加了客户端的复杂性。
2. 存在跨域请求，在一定场景下处理相对复杂。
3. 认证复杂，每个服务都需要独立认证。
4. 难以重构，随着项目的迭代，可能需要重新划分微服务。例如，可能将多个服务合并成一个或者将一个服务拆分成多个。如果客户端直接与微服务通信，那么重构将会很难实施。
5. 某些微服务可能使用了防火墙 / 浏览器不友好的协议，直接访问会有一定的困难。

以上这些问题可以借助 API 网关解决。API 网关是介于客户端和服务器端之间的中间层，所有的外部请求都会先经过 API 网关这一层。也就是说，API 的实现方面更多的考虑业务逻辑，而安全、性能、监控可以交由 API 网关来做，这样既提高业务灵活性又不缺安全性，典型的架构图如图所示：

使用 API 网关后的优点如下：

• 易于监控。可以在网关收集监控数据并将其推送到外部系统进行分析。
• 易于认证。可以在网关上进行认证，然后再将请求转发到后端的微服务，而无须在每个微服务中进行认证。
• 减少了客户端与各个微服务之间的交互次数。

API 网关选型

业界的情况：

我前面的文章<Netflix网关zuul(1.x和2.x)全解析>已经介绍了zuul1 和zuul2，现在就尝试从实例入手介绍一下spring cloud gateway

首先我们一步步实现一个最简单的网关例子

步骤1：在http://start.spring.io网站上创建一个spring-cloud-gateway-example项目，依赖spring-cloud-gateway，如下图所示

此时生产了一个spring-cloud-gateway-example的空项目包，pom.xml文件如下

<?xml version="1.0" encoding="UTF-8"?>
<projectxmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.3.RELEASE</version><relativePath/> <!--lookup parent from repository--></parent><groupId>com.example</groupId><artifactId>spring-cloud-gateway-example</artifactId><version>0.0.1-SNAPSHOT</version><name>spring-cloud-gateway-example</name><description>Demo project for Spring Boot</description><properties><java.version>1.8</java.version><spring-cloud.version>Greenwich.RELEASE</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-gateway</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></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></dependencies></dependencyManagement><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build><repositories><repository><id>spring-milestones</id><name>Spring Milestones</name><url>https://repo.spring.io/milestone</url></repository></repositories></project>

2.创建一个Route实例的配置类GatewayRoutes

packagecom.example.springcloudgatewayexample;importorg.springframework.cloud.gateway.route.RouteLocator;importorg.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;importorg.springframework.context.annotation.Bean;importorg.springframework.context.annotation.Configuration;
@Configurationpublic classGatewayRoutes {@BeanpublicRouteLocator routeLocator(RouteLocatorBuilder builder) {returnbuilder.routes().route(r->r.path("/java/**").filters(f-> f.stripPrefix(1)).uri("http://localhost:8090/helloWorld")).build();}
}

当然，也可以不适用配置类，使用配置文件，如下图所示

spring:cloud:gateway:routes: - predicates:- Path=/java/**filters:- StripPrefix=1uri: "http://localhost:8090/helloWorld"

不过，为了调试方便，我们使用配置类方式。

此时项目已经完成，足够简单吧。

3.启动此项目

>>因api网关需要转发到一个服务上，本文为http://localhost:8090/helloWorld，那需要先启动我上文<spring boot整合spring5-webflux从0开始的实战及源码解析>,你也可以创建一个普通的web项目，启动端口设置为8090，然后启动。

. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.1.3.RELEASE)2019-02-21 09:29:07.450 INFO 11704 --- [ main] c.e.demo.Spring5WebfluxApplication : Starting Spring5WebfluxApplication on DESKTOP-405G2C8 with PID 11704 (E:\workspaceForCloud\spring5-webflux\target\classes started by dell in E:\workspaceForCloud\spring5-webflux)
2019-02-21 09:29:07.455 INFO 11704 --- [ main] c.e.demo.Spring5WebfluxApplication : No active profile set, falling back to default profiles: default
2019-02-21 09:29:09.409 INFO 11704 --- [ main] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 8090
2019-02-21 09:29:09.413 INFO 11704 --- [ main] c.e.demo.Spring5WebfluxApplication : Started Spring5WebfluxApplication in 2.304 seconds (JVM running for 7.311)

>>以spring boot方式启动spring-cloud-gateway-example项目，日志如下

2019-02-21 10:34:33.435  INFO 8580 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration' of type [org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration$$EnhancerBySpringCGLIB$$1e059320] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying).   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.1.3.RELEASE)2019-02-21 10:34:33.767  INFO 8580 --- [           main] e.s.SpringCloudGatewayExampleApplication : No active profile set, falling back to default profiles: default
2019-02-21 10:34:34.219  INFO 8580 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=d98183ec-3e46-38ba-ba4c-e976a1017dce
2019-02-21 10:34:34.243  INFO 8580 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration' of type [org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration$$EnhancerBySpringCGLIB$$1e059320] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-02-21 10:34:44.367  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [After]
2019-02-21 10:34:44.367  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Before]
2019-02-21 10:34:44.367  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Between]
2019-02-21 10:34:44.367  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Cookie]
2019-02-21 10:34:44.367  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Header]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Host]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Method]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Path]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Query]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [ReadBodyPredicateFactory]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [RemoteAddr]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [Weight]
2019-02-21 10:34:44.368  INFO 8580 --- [           main] o.s.c.g.r.RouteDefinitionRouteLocator    : Loaded RoutePredicateFactory [CloudFoundryRouteService]
2019-02-21 10:34:44.920  INFO 8580 --- [           main] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8080
2019-02-21 10:34:44.923  INFO 8580 --- [           main] e.s.SpringCloudGatewayExampleApplication : Started SpringCloudGatewayExampleApplication in 12.329 seconds (JVM running for 13.126)

4.测试，浏览器访问http://localhost:8080/java/helloWorld

返回hello world ！

5.从上面的代码和配置及实例中，我们可以看出spring cloud gateway处理request请求的流程如下所示：

即在最前端，启动一个netty server（默认端口为8080）接受请求，然后通过Routes（每个Route由Predicate(等同于HandlerMapping)和Filter(等同于HandlerAdapter)）处理后通过Netty Client发给响应的微服务。

那么在gateway本身最重要的应该是Route（Netty Server和Client已经封装好了），它由RouteLocatorBuilder构建，内部包含Predicate和Filter，

    private Route(String id, URI uri, int order, AsyncPredicate<ServerWebExchange> predicate, List<GatewayFilter>gatewayFilters) {this.id =id;this.uri =uri;this.order =order;this.predicate =predicate;this.gatewayFilters =gatewayFilters;}

那么我们就来探讨一下这两个组件吧

5.1.Predicate

Predicte由PredicateSpec来构建，主要实现有：

以path为例

    /*** A predicate that checks if the path of the request matches the given pattern*@parampatterns the pattern to check the path against.*                The pattern is a {@linkorg.springframework.util.PathMatcher} pattern*@returna {@linkBooleanSpec} to be used to add logical operators*/publicBooleanSpec path(String... patterns) {return asyncPredicate(getBean(PathRoutePredicateFactory.class).applyAsync(c->c.setPatterns(Arrays.asList(patterns))));}

PathRoutePredicateFactory中执行

@Overridepublic Predicate<ServerWebExchange>apply(Config config) {final ArrayList<PathPattern> pathPatterns = new ArrayList<>();synchronized (this.pathPatternParser) {pathPatternParser.setMatchOptionalTrailingSeparator(config.isMatchOptionalTrailingSeparator());config.getPatterns().forEach(pattern->{PathPattern pathPattern= this.pathPatternParser.parse(pattern);pathPatterns.add(pathPattern);});}return exchange ->{PathContainer path=parsePath(exchange.getRequest().getURI().getPath());Optional<PathPattern> optionalPathPattern =pathPatterns.stream().filter(pattern->pattern.matches(path)).findFirst();if(optionalPathPattern.isPresent()) {PathPattern pathPattern=optionalPathPattern.get();traceMatch("Pattern", pathPattern.getPatternString(), path, true);PathMatchInfo pathMatchInfo=pathPattern.matchAndExtract(path);putUriTemplateVariables(exchange, pathMatchInfo.getUriVariables());return true;}else{traceMatch("Pattern", config.getPatterns(), path, false);return false;}};}

5.2.Filter

Filter分两种，一种GatewayFilter,一种GlobalFilter

5.2.1 GatewayFilter

GatewayFilter由GatewayFilterSpec构建，GatewayFilter的构建器

5.2.2 GlobalFilter

5.3 GlobalFilter和GatewayFilter的联系

FilteringWebHandler.GatewayFilterAdapter代理了GlobalFilter

6.总结

本文从一个spring-cloud-gateway实例入手，深入浅出的介绍了spring-cloud-gateway的组件，并从源码角度给出了实现的原理。

spring-cloud-gateway在最前端，启动一个netty server（默认端口为8080）接受请求，然后通过Routes（每个Route由Predicate(等同于HandlerMapping)和Filter(等同于HandlerAdapter)）处理后通过Netty Client发给响应的微服务。

Predicate和Filter的各个实现定义了spring-cloud-gateway拥有的功能。

参考资料：

【1】https://www.infoq.cn/article/comparing-api-gateway-performances

【2】https://dzone.com/articles/spring-cloud-gateway-configuring-a-simple-route