上篇文章我们已经完成了Ribbon负载均衡的功能。做法很简单，只需要在RestTemplate添加@LoanBalanced 的注解。默认情况下，Ribbon的负载均衡策略是RoundRobbin(轮训)的方式，可很多时候在特定场景下需要不同的策略，这个时候就需要自定义Ribbon策略了。看下面代码：
1. package com.zhuyang.cloud.controller;
2.
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.cloud.client.loadbalancer.LoadBalanced;
5. import org.springframework.cloud.netflix.ribbon.RibbonClient;
6. import org.springframework.context.annotation.Bean;
7. import org.springframework.web.bind.annotation.PathVariable;
8. import org.springframework.web.bind.annotation.RequestMapping;
9. import org.springframework.web.bind.annotation.RequestMethod;
10. import org.springframework.web.bind.annotation.RestController;
11. import org.springframework.web.client.RestTemplate;
12.
13. import com.zhuyang.cloud.entity.User;
14. import com.zhuyang.config.RibbonConfiguration;
15.
16. @RestController
17. @RibbonClient(name = "microservice-provider", configuration = RibbonConfiguration.class)//name是provider的服务名 <span style="font-family: Arial, Helvetica, sans-serif;">RibbonConfiguration为自定义配置</span>
18. public class MovieController {
19. @Bean
20. @LoadBalanced
21. public RestTemplate restTemplate() { // equals to RestTemplate
22. // restTemplate=new RestTemplate();
23. return new RestTemplate();
24. }
25.
26. @Autowired
27. private RestTemplate restTemplate;
28.
29. @RequestMapping(value = "/movie/{id}", method = RequestMethod.GET)
30. public User findById(@PathVariable Long id) {
31. // return restTemplate.getForEntity("http://localhost:8000/service/"+id,
32. // User.class).getBody();
33. return restTemplate.getForEntity("http://microservice-provider/provider/service/" + id, User.class).getBody();
34. }
35. }
1. server:
2. port: 8001
3. eureka:
4. client:
5. serviceUrl:
6. defaultZone: http://user:password123@localhost:8761/eureka/ # 指定注册中心的地址
7. instance:
8. preferIpAddress: true
9. spring:
10. application:
11. name: microservice-consumer
12. microservice-provider: ##config ribbon
13. ribbon:
14. eureka:
15. enabled: false
16. listOfServers: localhost:8000, localhost:8002,localhost:8003 ##假设provider有3台instance端口分别是8000 8002 8003
17. ServerListRefreshInterval: 15000
1. package com.zhuyang.config;
2.
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.context.annotation.Bean;
5.
6. import com.netflix.client.config.IClientConfig;
7. import com.netflix.loadbalancer.IPing;
8. import com.netflix.loadbalancer.IRule;
9. import com.netflix.loadbalancer.PingUrl;
10. import com.netflix.loadbalancer.ZoneAvoidanceRule;
11.
12. /**
13. *
14. * Here, we override the IPing and IRule used by the default load balancer. The
15. * default IPing is a NoOpPing (which doesn’t actually ping server instances,
16. * instead always reporting that they’re stable), and the default IRule is a
17. * ZoneAvoidanceRule (which avoids the Amazon EC2 zone that has the most
18. * malfunctioning servers, and might thus be a bit difficult to try out in our
19. * local environment).
20. *
21. */
22. public class RibbonConfiguration {
23. @Autowired
24. private IClientConfig ribbonClientConfig;
25.
26. /**
27. * Our IPing is a PingUrl, which will ping a URL to check the status of each
28. * server.provider has, as you’ll recall, a method mapped to the / path;
29. * that means that Ribbon will get an HTTP 200 response when it pings a
30. * running provider server.
31. *
32. * server list defined in application.yml :listOfServers: localhost:8000,
33. * localhost:8002,localhost:8003
34. *
35. */
36. @Bean
37. public IPing ribbonPing(IClientConfig config) {
38. // ping url will try to access http://microservice-provider/provider/ to
39. // see if reponse code is 200 . check PingUrl.isAlive()
40. // param /provider/ is the context-path of provider service
41. return new PingUrl(false, "/provider/");
42. }
43.
44. /**
45. * The IRule we set up, the AvailabilityFilteringRule, will use Ribbon’s
46. * built-in circuit breaker functionality to filter out any servers in an
47. * “open-circuit” state: if a ping fails to connect to a given server, or if
48. * it gets a read failure for the server, Ribbon will consider that server
49. * “dead” until it begins to respond normally.
50. *
51. * AvailabilityFilteringRule | 过滤掉那些因为一直连接失败的被标记为circuit tripped的后端server，并过滤掉那些高并发的的后端server（active connections 超过配置的阈值） | 使用一个AvailabilityPredicate来包含过滤server的逻辑，其实就就是检查status里记录的各个server的运行状态
52. * RandomRule | 随机选择一个server
53. * BestAvailabl eRule | 选择一个最小的并发请求的server | 逐个考察Server，如果Server被tripped了，则忽略，在选择其中
54. * RoundRobinRule | roundRobin方式轮询选择 | 轮询index，选择index对应位置的server
55. * WeightedResponseTimeRule | 根据响应时间分配一个weight，响应时间越长，weight越小，被选中的可能性越低。 | 一 个后台线程定期的从status里面读取评价响应时间，为每个server计算一个weight。Weight的计算也比较简单responsetime 减去每个server自己平均的responsetime是server的权重。当刚开始运行，没有形成statas时，使用roubine策略选择 server。
56. * RetryRule | 对选定的负载均衡策略机上重试机制。 | 在一个配置时间段内当选择server不成功，则一直尝试使用subRule的方式选择一个可用的server
57. * ZoneAvoidanceRule | 复合判断server所在区域的性能和server的可用性选择server | 使 用ZoneAvoidancePredicate和AvailabilityPredicate来判断是否选择某个server，前一个判断判定一个 zone的运行性能是否可用，剔除不可用的zone（的所有server），AvailabilityPredicate用于过滤掉连接数过多的 Server。
58. * @param config
59. * @return
60. */
61. @Bean
62. public IRule ribbonRule(IClientConfig config) {
63. // return new AvailabilityFilteringRule();
64. return new RandomRule();//
65. // return new BestAvailableRule();
66. // return new RoundRobinRule();//轮询
67. // return new WeightedResponseTimeRule();
68. // return new RetryRule();
69. // return new ZoneAvoidanceRule();
70. }
71. }
在RibbonConfiguration中的ribbonRule方法就是用来定义不用的策略，每种策略所对应的实现类和描述 都已经添加了注释。例如我们返回的是RandomRule策略，那么我们在多次请求provider的时候就不再是轮训的方式进行命中，而是随机方式。。下面是RandomRule的代码实现
1. public Server choose(ILoadBalancer lb, Object key) {
2. if (lb == null) {
3. return null;
4. }
5. null;
6.
7. while (server == null) {
8. if (Thread.interrupted()) {
9. return null;
10. }
11. //get all reachable server .list listOfServers: localhost:8000, localhost:8002,localhost:8003
12. List<Server> allList = lb.getAllServers();
13.
14. int serverCount = allList.size();
15. if (serverCount == 0) {
16. /*
17. * No servers. End regardless of pass, because subsequent passes
18. * only get more restrictive.
19. */
20. return null;
21. }
22.
23. int index = rand.nextInt(serverCount);//get random index
24. //get specified server eg:<span style="font-family: Arial, Helvetica, sans-serif;">localhost:8000</span>
25.
26. if (server == null) {
27. /*
28. * The only time this should happen is if the server list were
29. * somehow trimmed. This is a transient condition. Retry after
30. * yielding.
31. */
32. Thread.yield();
33. continue;
34. }
35.
36. if (server.isAlive()) {
37. return (server);
38. }
39.
40. // Shouldn't actually happen.. but must be transient or a bug.
41. null;
42. Thread.yield();
43. }
44.
45. return server;//return selected server
46.
47. }
48.
