原文地址:http://www.cnblogs.com/lulu/archive/2013/06/10/3130906.html
使用zookeeper 实现一致性hash。
redis服务启动时，将自己的路由信息通过临时节点方式写入zk，客户端通过zk client读取可用的路由信息。
服务端
使用python 脚本写的守护进程：https://github.com/LittlePeng/redis-manager脚本部署在redis-server本机，定时ping redis-server节点失效的情况：1.服务器与ZK服务器失去连接 Session Expired ，环境网络波动造成，需要根据网络情况设置适当zookeeper的Timeout时间，避免此情况发生2. 服务器宕机，Zookeeper server 发现zkclient ping超时，就会通知节点下线3. redis-server 挂了，redis-manager ping 超时主动断开与zookeeper server的连接客户端
需要zkclient监控 节点变化，及时更新路由策略
下面是C# 版本一致性hash算法：
1: class KetamaNodeLocator
2: {
3: private Dictionary<long,RedisCluster> ketamaNodes;
4: private HashAlgorithm hashAlg;
5: private int numReps = 160;
6: private long[] keys;
7:
8: public KetamaNodeLocator(List<RedisCluster> nodes)
9: {
10: ketamaNodes = new Dictionary<long,RedisCluster>();
11:
12: //对所有节点，生成nCopies个虚拟结点
13: for (int j = 0; j < nodes.Count; j++) {
14: RedisCluster node = nodes[j];
15: int numReps = node.Weight;
16:
17: //每四个虚拟结点为一组
18: for (int i = 0; i < numReps / 4; i++) {
19: byte[] digest = ComputeMd5(
20: String.Format("{0}_{1}_{2}",node.RoleName,node.RouteValue,i));
21:
22: /** Md5是一个16字节长度的数组，将16字节的数组每四个字节一组，
23: * 分别对应一个虚拟结点，这就是为什么上面把虚拟结点四个划分一组的原因*/
24: for (int h = 0; h < 4; h++) {
25:
26: long rv = ((long)(digest[3 + h * 4] & 0xFF) << 24)
27: | ((long)(digest[2 + h * 4] & 0xFF) << 16)
28: | ((long)(digest[1 + h * 4] & 0xFF) << 8)
29: | ((long)digest[0 + h * 4] & 0xFF);
30:
31: rv = rv & 0xffffffffL; /* Truncate to 32-bits */
32: ketamaNodes[rv] = node;
33: }
34: }
35: }
36:
37: keys = ketamaNodes.Keys.OrderBy(p => p).ToArray();
38: }
41: public RedisCluster GetWorkerNode(string k)
42: {
43: byte[] digest = ComputeMd5(k);
44: return GetNodeInner(Hash(digest,0));
45: }
46:
47: RedisCluster GetNodeInner(long hash)
48: {
49: if (ketamaNodes.Count == 0)
50: return null;
51: long key = hash;
52: int near = 0;
53: int index = Array.BinarySearch(keys,hash);
54: if (index < 0) {
55: near = (~index);
56: if (near == keys.Length)
57: near = 0;
58: }
59: else {
60: near = index;
61: }
62:
63: return ketamaNodes[keys[near]];
64: }
65:
66: public static long Hash(byte[] digest,int nTime)
67: {
68: long rv = ((long)(digest[3 + nTime * 4] & 0xFF) << 24)
69: | ((long)(digest[2 + nTime * 4] & 0xFF) << 16)
70: | ((long)(digest[1 + nTime * 4] & 0xFF) << 8)
71: | ((long)digest[0 + nTime * 4] & 0xFF);
72:
73: return rv & 0xffffffffL; /* Truncate to 32-bits */
74: }
79: public static byte[] ComputeMd5(string k)
80: {
81: MD5 md5 = new MD5CryptoServiceProvider();
82:
83: byte[] keyBytes = md5.ComputeHash(Encoding.UTF8.GetBytes(k));
84: md5.Clear();
85: return keyBytes;
86: }
87: }
