API 網關

API 網關出現的原因是微服務架構的出現，不同的微服務一般會有不同的網絡地址，而外部客戶端可能需要調用多個服務的接口才能完成一個業務需求，如果讓客戶端直接與各個微服務通信，會有以下的問題：

客戶端會多次請求不同的微服務，增加了客戶端的復雜性。

存在跨域請求，在一定場景下處理相對復雜。

認證復雜，每個服務都需要獨立認證。

難以重構，隨著項目的迭代，可能需要重新劃分微服務。例如，可能將多個服務合并成一個或者將一個服務拆分成多個。如果客戶端直接與微服務通信，那么重構將會很難實施。

某些微服務可能使用了防火墻 / 瀏覽器不友好的協議，直接訪問會有一定的困難。

以上這些問題可以借助 API 網關解決。API 網關是介于客戶端和服務器端之間的中間層，所有的外部請求都會先經過 API 網關這一層。也就是說，API 的實現方面更多的考慮業務邏輯，而安全、性能、監控可以交由 API 網關來做，這樣既提高業務靈活性又不缺安全性，典型的架構圖如圖所示：

使用 API 網關后的優點如下：

• 易于監控。可以在網關收集監控數據并將其推送到外部系統進行分析。
• 易于認證。可以在網關上進行認證，然后再將請求轉發到后端的微服務，而無須在每個微服務中進行認證。
• 減少了客戶端與各個微服務之間的交互次數。

API 網關選型

業界的情況：

我前面的文章<Netflix網關zuul(1.x和2.x)全解析>已經介紹了zuul1 和zuul2，現在就嘗試從實例入手介紹一下spring cloud gateway

首先我們一步步實現一個最簡單的網關例子

步驟1：在http://start.spring.io網站上創建一個spring-cloud-gateway-example項目，依賴spring-cloud-gateway，如下圖所示

此時生產了一個spring-cloud-gateway-example的空項目包，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.創建一個Route實例的配置類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 {@Beanpublic RouteLocator routeLocator(RouteLocatorBuilder builder) {return builder.routes().route(r ->r.path("/java/**").filters(f -> f.stripPrefix(1)).uri("http://localhost:8090/helloWorld")).build();} }

當然，也可以不適用配置類，使用配置文件，如下圖所示

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

不過，為了調試方便，我們使用配置類方式。

此時項目已經完成，足夠簡單吧。

3.啟動此項目

? >>因api網關需要轉發到一個服務上，本文為http://localhost:8090/helloWorld，那需要先啟動我上文<spring boot整合spring5-webflux從0開始的實戰及源碼解析>,你也可以創建一個普通的web項目，啟動端口設置為8090，然后啟動。

. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: 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方式啟動spring-cloud-gateway-example項目，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.測試，瀏覽器訪問http://localhost:8080/java/helloWorld

返回hello world ！

5.從上面的代碼和配置及實例中，我們可以看出spring cloud gateway處理request請求的流程如下所示：

即在最前端，啟動一個netty server（默認端口為8080）接受請求，然后通過Routes（每個Route由Predicate(等同于HandlerMapping)和Filter(等同于HandlerAdapter)）處理后通過Netty Client發給響應的微服務。

那么在gateway本身最重要的應該是Route（Netty Server和Client已經封裝好了），它由RouteLocatorBuilder構建，內部包含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;}

那么我們就來探討一下這兩個組件吧

5.1.Predicate

Predicte由PredicateSpec來構建，主要實現有：

以path為例

/*** 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中執行

@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分兩種，一種GatewayFilter,一種GlobalFilter

5.2.1 GatewayFilter

GatewayFilter由GatewayFilterSpec構建，GatewayFilter的構建器

?

5.2.2?GlobalFilter

5.3 GlobalFilter和GatewayFilter的聯系

FilteringWebHandler.GatewayFilterAdapter代理了GlobalFilter

6.總結

? 本文從一個spring-cloud-gateway實例入手，深入淺出的介紹了spring-cloud-gateway的組件，并從源碼角度給出了實現的原理。

? ?spring-cloud-gateway在最前端，啟動一個netty server（默認端口為8080）接受請求，然后通過Routes（每個Route由Predicate(等同于HandlerMapping)和Filter(等同于HandlerAdapter)）處理后通過Netty Client發給響應的微服務。

?Predicate和Filter的各個實現定義了spring-cloud-gateway擁有的功能。

參考資料：

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

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

轉載于:https://www.cnblogs.com/davidwang456/p/10411451.html

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