摘要:本文主要通过运用Spring Cloud Gateway的WeightRoutePredicateFactory对URL进行权重路由。

1.权重路由

1.1 权重路由使用场景

在开发或者测试的时候，或者线上发布，线上服务多版本控制的时候，需要对服务提供权重路由，最常见的使用就是，一个服务有两个版本，旧版本V1，新版本v2。在线上灰度的时候，需要通过网关动态实时推送，路由权重信息。比如95%的流量走服务v1版本，5%的流量走服务v2版本。

issue: The Spring Cloud Gateway issue of Allow Rolling Deployments https://github.com/spring-cloud/spring-cloud-gateway/issues/67

1.2 Spring Cloud Gateway权重路由原理

Spring Cloud Gateway中提供了 org.springframework.cloud.gateway.handler.predicate.WeightRoutePredicateFactory去实现根据分组设置权重进行路由，因此使用起来相对比较简单，有兴趣的可以debug阅读源码。

1. public class WeightRoutePredicateFactory extends AbstractRoutePredicateFactory<WeightConfig> implements ApplicationEventPublisherAware {

2. private static final Log log = LogFactory.getLog(WeightRoutePredicateFactory.class);

3. public static final String GROUP_KEY = WeightConfig.CONFIG_PREFIX + ".group";

4. public static final String WEIGHT_KEY = WeightConfig.CONFIG_PREFIX + ".weight";

5. private ApplicationEventPublisher publisher;

6. public WeightRoutePredicateFactory() {

7. super(WeightConfig.class);

8. }

9. [@Override](https://my.oschina.net/u/1162528)

10. public void setApplicationEventPublisher(ApplicationEventPublisher publisher) {

11. this.publisher = publisher;

12. }

13. [@Override](https://my.oschina.net/u/1162528)

14. public List<String> shortcutFieldOrder() {

15. return Arrays.asList(GROUP_KEY, WEIGHT_KEY);

16. }

17. [@Override](https://my.oschina.net/u/1162528)

18. public String shortcutFieldPrefix() {

19. return WeightConfig.CONFIG_PREFIX;

20. }

21. [@Override](https://my.oschina.net/u/1162528)

22. public void beforeApply(WeightConfig config) {

23. if (publisher != null) {

24. publisher.publishEvent(new WeightDefinedEvent(this, config));

25. }

26. }

27. [@Override](https://my.oschina.net/u/1162528)

28. public Predicate<ServerWebExchange> apply(WeightConfig config) {

29. return exchange -> {

30. Map<String, String> weights = exchange.getAttributeOrDefault(WEIGHT_ATTR,

31. Collections.emptyMap());

32. String routeId = exchange.getAttribute(GATEWAY_PREDICATE_ROUTE_ATTR);

33. // all calculations and comparison against random num happened in

34. // WeightCalculatorWebFilter

35. String group = config.getGroup();

36. if (weights.containsKey(group)) {

37. String chosenRoute = weights.get(group);

38. if (log.isTraceEnabled()) {

39. log.trace("in group weight: "+ group + ", current route: " + routeId +", chosen route: " + chosenRoute);

40. }

41. return routeId.equals(chosenRoute);

42. }

43. return false;

44. };

45. }

46. }

2.Spring Cloud Gateway中的权重路由案例

2.1 案例代码地址

https://github.com/SoftwareKing/sc-gateway/tree/master/ch4

2.2 Spring Cloud Gateway Server说明

Spring Cloud Gateway will dispatch 95% of the requests to version 1 and 5% of the traffic to version 2 of a specified service, as shown by the following figure.

我们通过在Spring Cloud Gateway中会配置不同的权重信息到不同URL上，Spring Cloud Gateway会根据我们配置的路由权重信息，将请求分发到不同的源服务组，权重信息如ch4/ch4-gateway中的application.yml所示，主要配置信息如下。

1. spring:

2. application:

3. name: ch4-gateway

4. cloud:

5. gateway:

6. routes:

7. - id: service1_v1

8. uri: http://localhost:8081/v1

9. predicates:

10. - Path=/test

11. - Weight=service1, 95

12. - id: service1_v2

13. uri: http://localhost:8081/v2

14. predicates:

15. - Path=/test

16. - Weight=service1, 5

Weight=service1, 95，Weight=service1, 5就是路由的权重信息。

2.3 源服务

源服务在本案例中源服务如ch4-service-provider所示，主要提提供Gateway Server权重路由对应的后端源服务。因为比较简单因此不做详细说明，主要代码如下所示。

1. package org.xujin.sc.service;

2. import org.springframework.web.bind.annotation.RequestMapping;

3. import org.springframework.web.bind.annotation.RestController;

4. import reactor.core.publisher.Mono;

5. @RestController

6. public class ServiceController {

7. @RequestMapping(value = "/v1", produces = "text/plain;charset=UTF-8")

8. public Mono<String> v1() {

9. return Mono.just("v1");

10. }

11. @RequestMapping(value = "/v2", produces = "text/plain;charset=UTF-8")

12. public Mono<String> v2() {

13. return Mono.just("v2");

14. }

15. }

2.4 测试

分别启动ch4-gateway，ch4-service-provider进行访问:http://localhost:8080/test 测试,发现会根据所设权重进行路由。