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本帖最后由 小江哥 于 2019-11-22 15:55 编辑

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] 纯文本查看 复制代码
<?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 [url]http://maven.apache.org/xsd/maven-4.0.0.xsd[/url]">    <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>[url]https://repo.spring.io/milestone</url>[/url]        </repository>    </repositories></project>[url=]

2.创建一个Route实例的配置类GatewayRoutes
[Java] 纯文本查看 复制代码
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;@Configurationpublic 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
[Java] 纯文本查看 复制代码
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。
[Shell] 纯文本查看 复制代码
. ____ _ __ _ _/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/ ___)| |_)| | | | | || (_| | ) ) ) )' |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: 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: default2019-02-21 09:29:09.409 INFO 11704 --- [ main] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 80902019-02-21 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
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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: default2019-02-21 10:34:34.219  INFO 8580 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=d98183ec-3e46-38ba-ba4c-e976a1017dce2019-02-21 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): 80802019-02-21 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,
[Java] 纯文本查看 复制代码
    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
[Java] 纯文本查看 复制代码
    /**     * 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
[Java] 纯文本查看 复制代码
 @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:

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