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：
- 客户端会多次请求不同的微服务，增加了客户端的复杂性。
- 存在跨域请求，在一定场景下处理相对复杂。
- 认证复杂，每个服务都需要独立认证。
- 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。
- 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"?> <project xmlns="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
package com.example.springcloudgatewayexample; import org.springframework.cloud.gateway.route.RouteLocator; import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class GatewayRoutes { @Bean public RouteLocator routeLocator(RouteLocatorBuilder builder) { return builder.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=1
uri: "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 * @param patterns the pattern to check the path against. * The pattern is a {@link org.springframework.util.PathMatcher} pattern * @return a {@link BooleanSpec} to be used to add logical operators */ public BooleanSpec path(String... patterns) { return asyncPredicate(getBean(PathRoutePredicateFactory.class) .applyAsync(c -> c.setPatterns(Arrays.asList(patterns)))); }
PathRoutePredicateFactory中执行
@Override public 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