目录
一致性哈希算法 - 负载均衡
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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
