我們來了解一下負載均衡的源碼,是怎么實現的,它是怎么實現的,開始我們說了第三種方式只是用了一個注解,實質上是和第二種方式是一模一樣的,那么為了方便觀察呢,這里使用第二種方式,來查看源碼ServiceInstance serviceInstance = this.loadBalancerClient.choose("PRODUCT");這里調用了choose這種方法,我們點進來可以看到他的一個接口/*** Implemented by classes which use a load balancer to choose a server to* send a request to.** @author Ryan Baxter*/ public interface ServiceInstanceChooser {/*** Choose a ServiceInstance from the LoadBalancer for the specified service* @param serviceId the service id to look up the LoadBalancer* @return a ServiceInstance that matches the serviceId*/ServiceInstance choose(String serviceId); }按進來跳到他的實現,看一下他的實現類public class RibbonLoadBalancerClient implements LoadBalancerClient {可以看到他實現了一個接口,LoadBalancerClient,LoadBalancerClient又繼承了一個ServiceInstanceChooser/*** Represents a client side load balancer* @author Spencer Gibb*/ public interface LoadBalancerClient extends ServiceInstanceChooser {注意我們看源碼的時候呢,可以這樣子來看,比如我已經進入到這個類里面了,你想看他類之間的關系的話,回到我們要觀察的方法@Override public ServiceInstance choose(String serviceId) {Server server = getServer(serviceId);if (server == null) {return null;}return new RibbonServer(serviceId, server, isSecure(server, serviceId),serverIntrospector(serviceId).getMetadata(server)); }我們知道他第一步要把服務列表要給找出來,你看到這個方法protected Server getServer(String serviceId) {return getServer(getLoadBalancer(serviceId)); }然后又繼續往下找protected Server getServer(ILoadBalancer loadBalancer) {if (loadBalancer == null) {return null;}return loadBalancer.chooseServer("default"); // TODO: better handling of key }可以看到他這里用了哪個去找,用的是一個ILoadBalancer,看一下這個/*** Interface that defines the operations for a software loadbalancer. A typical* loadbalancer minimally need a set of servers to loadbalance for, a method to* mark a particular server to be out of rotation and a call that will choose a* server from the existing list of server.* * @author stonse* */ public interface ILoadBalancer {他用的這個組件去找,這個組件就是屬于Ribbo下面的com.netflix.loadbalancer.ILoadBalancer所以說他一旦用了負載均衡的技術,都是Ribbon,我們可以看這個方法protected Server getServer(ILoadBalancer loadBalancer) {if (loadBalancer == null) {return null;}return loadBalancer.chooseServer("default"); // TODO: better handling of key }這里有幾個選擇,我們就選擇com.netflix.loadbalancer.BaseLoadBalancer.chooseServer(Object)/** Get the alive server dedicated to key* * @return the dedicated server*/ public Server chooseServer(Object key) {if (counter == null) {counter = createCounter();}counter.increment();if (rule == null) {return null;} else {try {return rule.choose(key);} catch (Exception e) {logger.warn("LoadBalancer [{}]: Error choosing server for key {}", name, key, e);return null;}} }進來之后同樣的可以觀察這個類之間的關系,這個就比上一個復雜一些了public class BaseLoadBalancer extends AbstractLoadBalancerpublic abstract class AbstractLoadBalancer implements ILoadBalancer {看一下ILoadBalancer接口,這里有一個getServerList/*** @deprecated 2016-01-20 This method is deprecated in favor of the* cleaner {@link #getReachableServers} (equivalent to availableOnly=true)* and {@link #getAllServers} API (equivalent to availableOnly=false).** Get the current list of servers.** @param availableOnly if true, only live and available servers should be returned*/ @Deprecated public List<Server> getServerList(boolean availableOnly);這個已經標記廢棄了,getAllServers這個還在用/*** @return All known servers, both reachable and unreachable.*/ public List<Server> getAllServers();所以我們斷定獲取所有服務列表,肯定是在這個方法com.netflix.loadbalancer.BaseLoadBalancer.getAllServers()@Override public List<Server> getAllServers() {return Collections.unmodifiableList(allServerList); }這里我們要獲取列表,所以我們啟動兩個實例,由于服務剛剛啟動完成,還沒來得及獲取服務列表,你就來訪問就來刷新,所以會遇到這個問題,你看這個日志剛剛報了個錯之后,DiscoveryClient打印出的日志,他去獲取所有已經注冊了的服務,這個時候才去獲取,這個時候我們再來訪問,此時能夠獲取服務列表了,就是把這個list作為不能再修改的Listlocalhost:8081/getProductMsghttp://10.40.8.144:8080/msg這是第一步獲取服務列表,我們再來看一下他的負載均衡策略,/** Get the alive server dedicated to key* * @return the dedicated server*/ public Server chooseServer(Object key) {if (counter == null) {counter = createCounter();}counter.increment();if (rule == null) {return null;} else {try {return rule.choose(key);} catch (Exception e) {logger.warn("LoadBalancer [{}]: Error choosing server for key {}", name, key, e);return null;}} }我們關心的是規則了protected IRule rule = DEFAULT_RULE;有個默認的規則private final static IRule DEFAULT_RULE = new RoundRobinRule();默認的規則是什么,通過名字也能夠看出來吧,就是輪詢的方式,那我們可以來測試一下,看到底是不是輪詢,把Product兩個都給啟動了,為了以示區別@RestController public class ClientController {// @Autowired // private RestTemplate restTemplate;@Autowiredprivate LoadBalancerClient loadBalancerClient;@GetMapping("/getProductMsg")public String getProductMsg() {// 1.第一種方式(直接使用RestTemplate,url寫死)RestTemplate restTemplate = new RestTemplate(); // String response = restTemplate.getForObject("http://localhost:8080/msg", String.class); // System.out.println(response);// 第二種方式(利用loadBalancerClient通過應用名獲取url,然后再使用restTemplate 注意這里不能用第三種的restTemplate)ServiceInstance serviceInstance = this.loadBalancerClient.choose("product");String url = String.format("http://%s:%s", serviceInstance.getHost(),serviceInstance.getPort()+"/msg");System.out.println(url);return restTemplate.getForObject(url, String.class);// 3.第三種方式(利用@LoadBalanced,可以在restTemplate里使用應用名字) // String response = restTemplate.getForObject("http://PRODUCT/msg", String.class); // System.out.println(response); // return response;} }一個是8080,一個是9080localhost:8080/msglocalhost:9080/msg可以看到他時輪詢出現的,這里有三個負載均衡類,他用的到底是哪一個呢,我們可以重啟一下,日志里面也會打印出來,public DynamicServerListLoadBalancer(IClientConfig clientConfig, IRule rule, IPing ping,ServerList<T> serverList, ServerListFilter<T> filter,ServerListUpdater serverListUpdater) {super(clientConfig, rule, ping);this.serverListImpl = serverList;this.filter = filter;this.serverListUpdater = serverListUpdater;if (filter instanceof AbstractServerListFilter) {((AbstractServerListFilter) filter).setLoadBalancerStats(getLoadBalancerStats());}restOfInit(clientConfig); }就是我們剛剛說到的輪詢,那假如我們想改變負載均衡的規則,其實一般情況下我們不需要改變,你基本上用這個輪詢就可以了,假如需要自己定義的時候,直接在配置里面加一個配置就行了,這個配置很長,不建議大家去記,https://cloud.spring.io/spring-cloud-static/Finchley.SR4/multi/multi_spring-cloud.html我們搜索Ribbon關鍵字,看目錄里面,最好在目錄里面搜到,我們直接通過配置文件就可以配置了https://cloud.spring.io/spring-cloud-static/Finchley.SR4/multi/multi_spring-cloud-ribbon.html# _customizing_the_default_for_all_ribbon_clients16.4 Customizing the Ribbon Client by Setting Propertiesusers:ribbon:NIWSServerListClassName: com.netflix.loadbalancer.ConfigurationBasedServerListNFLoadBalancerRuleClassName: com.netflix.loadbalancer.WeightedResponseTimeRule這個就是表示我們要配置的ClassName,order.ribbon.NFLoadBalancerRuleClassName=com.netflix.loadbalancer.RoundRobinRuleZoneAvoidanceRule

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