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本文主要研究一下spring cloud gateway如何集成hystrix

maven

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>

添加spring-cloud-starter-netflix-hystrix依赖，开启hystrix

配置实例

hystrix.command.fallbackcmd.execution.isolation.thread.timeoutInMilliseconds: 5000
spring:
  cloud:
    gateway:
      discovery:
        locator:
          enabled: true
      routes:
      - id: employee-service
        uri: lb://employee-service
        predicates:
        - Path=/employee/**
        filters:
        - RewritePath=/employee/(?<path>.*), /$\{path}
        - name: Hystrix
          args:
            name: fallbackcmd
            fallbackUri: forward:/fallback

首先filter里头配置了name为Hystrix的filter，实际是对应HystrixGatewayFilterFactory
然后指定了hystrix command的名称，及fallbackUri，注意fallbackUri要以forward开头
最后通过hystrix.command.fallbackcmd.execution.isolation.thread.timeoutInMilliseconds指定该command的超时时间

fallback实例

@RestController
@RequestMapping("/fallback")
public class FallbackController {

    @RequestMapping("")
    public String fallback(){
        return "error";
    }
}

源码解析

GatewayAutoConfiguration

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@Configuration
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@EnableConfigurationProperties
@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)
@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})
@ConditionalOnClass(DispatcherHandler.class)
public class GatewayAutoConfiguration {
    //......
	@Configuration
	@ConditionalOnClass({HystrixObservableCommand.class, RxReactiveStreams.class})
	protected static class HystrixConfiguration {
		@Bean
		public HystrixGatewayFilterFactory hystrixGatewayFilterFactory(DispatcherHandler dispatcherHandler) {
			return new HystrixGatewayFilterFactory(dispatcherHandler);
		}
	}
    //......
}

引入spring-cloud-starter-netflix-hystrix类库，就有HystrixObservableCommand.class, RxReactiveStreams.class，便开启HystrixConfiguration

HystrixGatewayFilterFactory

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/filter/factory/HystrixGatewayFilterFactory.java

/**
 * Depends on `spring-cloud-starter-netflix-hystrix`, {@see http://cloud.spring.io/spring-cloud-netflix/}
 * @author Spencer Gibb
 */
public class HystrixGatewayFilterFactory extends AbstractGatewayFilterFactory<HystrixGatewayFilterFactory.Config> {

	public static final String FALLBACK_URI = "fallbackUri";

	private final DispatcherHandler dispatcherHandler;

	public HystrixGatewayFilterFactory(DispatcherHandler dispatcherHandler) {
		super(Config.class);
		this.dispatcherHandler = dispatcherHandler;
	}

	@Override
	public List<String> shortcutFieldOrder() {
		return Arrays.asList(NAME_KEY);
	}

	public GatewayFilter apply(String routeId, Consumer<Config> consumer) {
		Config config = newConfig();
		consumer.accept(config);

		if (StringUtils.isEmpty(config.getName()) && !StringUtils.isEmpty(routeId)) {
			config.setName(routeId);
		}

		return apply(config);
	}

	@Override
	public GatewayFilter apply(Config config) {
		//TODO: if no name is supplied, generate one from command id (useful for default filter)
		if (config.setter == null) {
			Assert.notNull(config.name, "A name must be supplied for the Hystrix Command Key");
			HystrixCommandGroupKey groupKey = HystrixCommandGroupKey.Factory.asKey(getClass().getSimpleName());
			HystrixCommandKey commandKey = HystrixCommandKey.Factory.asKey(config.name);

			config.setter = Setter.withGroupKey(groupKey)
					.andCommandKey(commandKey);
		}

		return (exchange, chain) -> {
			RouteHystrixCommand command = new RouteHystrixCommand(config.setter, config.fallbackUri, exchange, chain);

			return Mono.create(s -> {
				Subscription sub = command.toObservable().subscribe(s::success, s::error, s::success);
				s.onCancel(sub::unsubscribe);
			}).onErrorResume((Function<Throwable, Mono<Void>>) throwable -> {
				if (throwable instanceof HystrixRuntimeException) {
					HystrixRuntimeException e = (HystrixRuntimeException) throwable;
					if (e.getFailureType() == TIMEOUT) { //TODO: optionally set status
						setResponseStatus(exchange, HttpStatus.GATEWAY_TIMEOUT);
						return exchange.getResponse().setComplete();
					}
				}
				return Mono.error(throwable);
			}).then();
		};
	}
    //......
}

这里创建了RouteHystrixCommand，将其转换为Mono，然后在onErrorResume的时候判断如果HystrixRuntimeException的failureType是FailureType.TIMEOUT类型的话，则返回GATEWAY_TIMEOUT(504, "Gateway Timeout")状态码。

RouteHystrixCommand

//TODO: replace with HystrixMonoCommand that we write
private class RouteHystrixCommand extends HystrixObservableCommand<Void> {

	private final URI fallbackUri;
	private final ServerWebExchange exchange;
	private final GatewayFilterChain chain;

	RouteHystrixCommand(Setter setter, URI fallbackUri, ServerWebExchange exchange, GatewayFilterChain chain) {
		super(setter);
		this.fallbackUri = fallbackUri;
		this.exchange = exchange;
		this.chain = chain;
	}

	@Override
	protected Observable<Void> construct() {
		return RxReactiveStreams.toObservable(this.chain.filter(exchange));
	}

	@Override
	protected Observable<Void> resumeWithFallback() {
		if (this.fallbackUri == null) {
			return super.resumeWithFallback();
		}

		//TODO: copied from RouteToRequestUrlFilter
		URI uri = exchange.getRequest().getURI();
		//TODO: assume always?
		boolean encoded = containsEncodedParts(uri);
		URI requestUrl = UriComponentsBuilder.fromUri(uri)
				.host(null)
				.port(null)
				.uri(this.fallbackUri)
				.build(encoded)
				.toUri();
		exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);

		ServerHttpRequest request = this.exchange.getRequest().mutate().uri(requestUrl).build();
		ServerWebExchange mutated = exchange.mutate().request(request).build();
		return RxReactiveStreams.toObservable(HystrixGatewayFilterFactory.this.dispatcherHandler.handle(mutated));
	}
}

这里重写了construct方法，RxReactiveStreams.toObservable(this.chain.filter(exchange))，将reactor的Mono转换为rxjava的Observable
这里重写了resumeWithFallback方法，针对有fallbackUri的情况，重新路由到fallbackUri的地址

Config

public static class Config {
	private String name;
	private Setter setter;
	private URI fallbackUri;

	public String getName() {
		return name;
	}

	public Config setName(String name) {
		this.name = name;
		return this;
	}

	public Config setFallbackUri(String fallbackUri) {
		if (fallbackUri != null) {
			setFallbackUri(URI.create(fallbackUri));
		}
		return this;
	}

	public URI getFallbackUri() {
		return fallbackUri;
	}

	public void setFallbackUri(URI fallbackUri) {
		if (fallbackUri != null && !"forward".equals(fallbackUri.getScheme())) {
			throw new IllegalArgumentException("Hystrix Filter currently only supports 'forward' URIs, found " + fallbackUri);
		}
		this.fallbackUri = fallbackUri;
	}

	public Config setSetter(Setter setter) {
		this.setter = setter;
		return this;
	}
}

可以看到Config校验了fallbackUri，如果不为null，则必须以forward开头

小结

spring cloud gateway集成hystrix，分为如下几步：

添加spring-cloud-starter-netflix-hystrix依赖
在对应route的filter添加name为Hystrix的filter，同时指定hystrix command的名称，及其fallbackUri(可选)
指定该hystrix command的超时时间等。

doc

112.4 Hystrix GatewayFilter Factory

芋道源码 —— 纯源码解析博客

Spring Cloud Gateway 集成 Hystrix实战

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