[TOC] # 目录 ## 一致性哈希算法 - 负载均衡 ### CodeView ```java package com.example.springcloud.rules; import com.netflix.client.config.IClientConfig; import com.netflix.loadbalancer.AbstractLoadBalancerRule; import com.netflix.loadbalancer.IRule; import com.netflix.loadbalancer.Server; import lombok.NoArgsConstructor; import org.springframework.util.CollectionUtils; import org.springframework.web.context.request.RequestContextHolder; import org.springframework.web.context.request.ServletRequestAttributes; import org.springframework.web.servlet.support.RequestContext; import javax.servlet.http.HttpServletRequest; import java.io.UnsupportedEncodingException; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.List; import java.util.Objects; import java.util.SortedMap; import java.util.TreeMap; /** * @author eddie.lee * @ProjectName springcloud-demo-dec * @Package com.example.springcloud.rules * @ClassName MyRule * @blog blog.eddilee.cn * @description 一致性哈希算法 - 负载均衡 * @date created in 2021-01-11 23:23 * @modified by */ @NoArgsConstructor public class MyRule extends AbstractLoadBalancerRule implements IRule { /** * 虚拟节点数 */ public static final int VIRTUAL_NODE_NUM = 8; @Override public void initWithNiwsConfig(IClientConfig iClientConfig) { } @Override public Server choose(Object o) { HttpServletRequest request = ((ServletRequestAttributes) Objects.requireNonNull(RequestContextHolder.getRequestAttributes())).getRequest(); String uri = request.getServletPath() + "?" + request.getQueryString(); // hashCode() = int; return route(uri.hashCode(), getLoadBalancer().getAllServers()); } public Server route(int hashId, List<Server> addressList) { if (CollectionUtils.isEmpty(addressList)) { return null; } // 首先是将node定位到圆上,我们以 hash - address方式定位 // 因为后面需要获取离jobId最近node所以将数据放入到TreeMap中 TreeMap<Long, Server> address = new TreeMap<>(); addressList.stream().forEach(e -> { // 将每个node虚拟化为8个节点 for (int i = 0; i < VIRTUAL_NODE_NUM; i++) { // long hash = hash("SHARD-" + address + "-NODE-" + i); // address.put(hash, e); long hash = hash(e.getId() + i); address.put(hash, e); } }); long hash = hash(String.valueOf(hashId)); // 这里是顺时针转动jobHash寻找node的策略,其实就是寻找node哈希值大于等于jobId哈希值的最近一个node SortedMap<Long, Server> last = address.tailMap(hash); // 当request URL的hash值大于任意一个服务器对应的hashKey. // 取address中的第一个节点 if (last.isEmpty()) { address.firstEntry().getValue(); } // if (!last.isEmpty()) { // return last.get(last.firstKey()); // } // 如果请求落在最大一组hash上,那么就返回第一个node return last.get(last.firstKey()); } public long hash(String key) { MessageDigest md5; try { md5 = MessageDigest.getInstance("MD5"); } catch (NoSuchAlgorithmException e) { throw new RuntimeException("MD5 not supported", e); } byte[] keyByte = null; keyByte = key.getBytes(StandardCharsets.UTF_8); md5.update(keyByte); byte[] digest = md5.digest(); long hashCode = ((long) (digest[3] & 0xFF) << 24) | ((long) (digest[2] & 0xFF) << 16) | ((long) (digest[1] & 0xFF) << 8) | ((long) (digest[0] & 0xFF)); return hashCode & 0xffffffffL; } } ``` ### How to test? - 通过PostMan测试 - localhost:31000/sayHi?test=32123 得到 This is 30002 - localhost:31000/sayHi?test=456456 得到 This is 30001 > test=xxx 其实可以对应你的服务器id,或者某些服务应用标识 ### 参考资料 - [一致性哈希算法](https://yq.aliyun.com/articles/297025) - [负载均衡之一致性哈希算法](https://blog.csdn.net/javamoo/article/details/79646095) - [SpringCloud Ribbon组件介绍 - 旧版](https://github.com/eddie-code/SpringCloudDemo) - [SpringCloud Ribbon组件介绍 - 新版](https://github.com/eddie-code/springcloud-demo-dec)