从0开始构建你的api网关--Spring Cloud Gateway网关实战及原理解析

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