redis是个分布式缓存，与传统数据库最大的优势，在于它的“分布式”上。
分布式的优势：
容易实现容量的扩展
数据的均等分布
很好的高可用性
redis 和memcached是分布式缓存的两款流行方案，他们之间的对比
| redis | memcached | |
| 主从功能 | Replication 支持 主备自动切换 | 本身不支持，可以通过客户端自己实现 |
| 键值一致性 | 哈希槽 | 一致性哈希 |
| 集群 | 服务端支持（但是beta版） unstable | 由客户端实现 |
| 工具支持 | 提供自带的工具（客户端redis-cli,check-rdb...） | 较弱 |
| 数据存储 | 支持 | 不支持，重启数据丢失 |
本章主要内容
安装一个三主的redis集群环境。
准备
由于本人没有接触过ruby语言，在安装之前做功课时，需要安装ruby环境等，心理上有了点小负担，担心遇到麻烦。后来，不出所料遇到了点麻烦。最后，还是安装成功了，回头想想，没有什么可担心的，无外乎失败了重装，真是年纪越大，胆子越小啊。我采用的方式，“兵来将挡，水来土掩”，有错就解决错，一步步安装。借助网络的力量，逐个把问题击破。
安装ruby环境
1.安装ruby
遇到的问题
未安装ruby
版本过低
未安装rubygem
gem源出错
请参考
2. 编译redis cluster
从https://github.com/antirez/redis/branches下载unstable版本。
编译 make
此时,在/usr/local/src/redis-unstable/src 目录下生成了支持cluster的redis-server
3.建立集群环境
1.建立目录 cp /usr/local/redis mkdir cluster-test cd cluster-test/ mkdir 7000 mkdir 7001 mkdir 7002 2.复制redis-server cp /usr/local/src/redis-unstable/src/redis-server /usr/local/redis/cluster-test/7001 cp /usr/local/src/redis-unstable/src/redis-server /usr/local/redis/cluster-test/7000 cp /usr/local/src/redis-unstable/src/redis-server /usr/local/redis/cluster-test/7002 #集群管理工具（为了方便，将他复制到合适位置） cp /usr/local/src/redis-unstable/src/redis-trib.rb /usr/local/redis/cluster-test
3.建立3个cluster 节点对应的redis.conf文件
[root@hadoop2 cluster-test]# vi 7000/redis.conf port 7000 cluster-enabled yes cluster-config-file nodes.conf cluster-node-timeout 5000 appendonly yes daemonize yes logfile "redis7000.log" #这是最简单的集群参数
其他7001/redis.conf,7002.conf文件， 仅仅port和logfile参数不同，其他一样。
此时 7000, 7001,7002目录下，只有2个文件,分别是 redis-server,redis.conf
4. 启动（分别启动3个主节点）
cd 7000 ./redis-server ./redis.conf cd ../7001/ ./redis-server ./redis.conf cd ../7002 ./redis-server ./redis.conf
对应某个节点日志
26361:M 10 Sep 21:13:22.054 * No cluster configuration found, I'm 7f242cf2c7ce5d84103638c5017f2204e1509f4c
_._
_.-``__ ''-._
_.-`` `. `_. ''-._ Redis 3.2.3 (00000000/0) 32 bit
.-`` .-```. ```\/ _.,_ ''-._
( ' , .-` | `, ) Running in cluster mode
|`-._`-...-` __...-.``-._|'` _.-'| Port: 7001
| `-._ `._ / _.-' | PID: 26361
`-._ `-._ `-./ _.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' | http://redis.io
`-._ `-._`-.__.-'_.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' |
`-._ `-._`-.__.-'_.-' _.-'
`-._ `-.__.-' _.-'
`-._ _.-'
`-.__.-'
26361:M 10 Sep 21:13:22.075 # Server started, Redis version 3.2.3
26361:M 10 Sep 21:13:22.075 * DB loaded from append only file: 0.000 seconds
26361:M 10 Sep 21:13:22.076 # I have keys for unassigned slot 5659. Taking responsibility for it.
26361:M 10 Sep 21:13:22.076 # I have keys for unassigned slot 9980. Taking responsibility for it.
26361:M 10 Sep 21:13:22.080 * The server is now ready to accept connections on port 7001
5. 建立集群
./redis-trib.rb create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002
[root@hadoop2 cluster-test]# ./redis-trib.rb create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002
>>> Creating cluster
>>> Performing hash slots allocation on 3 nodes...
Using 3 masters:
127.0.0.1:7000
127.0.0.1:7001
127.0.0.1:7002
M: 5ad201ebdf0553690295dcd06f89f15750e73989 127.0.0.1:7000
slots:0-5460 (5461 slots) master
M: 7f242cf2c7ce5d84103638c5017f2204e1509f4c 127.0.0.1:7001
slots:5461-10922 (5462 slots) master
M: 8ea7b0976e4848653435e4e77af311a6ade330a8 127.0.0.1:7002
slots:10923-16383 (5461 slots) master
Can I set the above configuration? (type 'yes' to accept): yes
>>> Nodes configuration updated
>>> Assign a different config epoch to each node
>>> Sending CLUSTER MEET messages to join the cluster
Waiting for the cluster to join.
>>> Performing Cluster Check (using node 127.0.0.1:7000)
M: 5ad201ebdf0553690295dcd06f89f15750e73989 127.0.0.1:7000
slots:0-5460 (5461 slots) master
0 additional replica(s)
M: 8ea7b0976e4848653435e4e77af311a6ade330a8 127.0.0.1:7002
slots:10923-16383 (5461 slots) master
0 additional replica(s)
M: 7f242cf2c7ce5d84103638c5017f2204e1509f4c 127.0.0.1:7001
slots:5461-10922 (5462 slots) master
0 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
这时候主节点日志
26536:M 10 Sep 21:25:32.360 * DB loaded from append only file: 0.000 seconds
26536:M 10 Sep 21:25:32.361 * The server is now ready to accept connections on port 7000
26536:M 10 Sep 21:27:54.651 # configEpoch set to 1 via CLUSTER SET-CONFIG-EPOCH
26536:M 10 Sep 21:27:54.660 # IP address for this node updated to 127.0.0.1
26536:M 10 Sep 21:27:59.619 # Cluster state changed: ok
6.测试
[root@hadoop2 cluster-test]# /usr/local/redis/bin/redis-cli -c -p 7000 127.0.0.1:7000> keys * (empty list or set) 127.0.0.1:7000> set title "cluster1" OK 127.0.0.1:7000> set title1 "cluster1" OK 127.0.0.1:7000> set title2 "cluster1" -> Redirected to slot [14045] located at 127.0.0.1:7002 OK 127.0.0.1:7002> set title5 "cluster4" -> Redirected to slot [1594] located at 127.0.0.1:7000 OK 127.0.0.1:7000> set title3 "cluster4" -> Redirected to slot [9980] located at 127.0.0.1:7001 OK 127.0.0.1:7001> get title -> Redirected to slot [2217] located at 127.0.0.1:7000 "cluster1" 127.0.0.1:7000> get title2 -> Redirected to slot [14045] located at 127.0.0.1:7002 "cluster8111" 127.0.0.1:7002> get title3 -> Redirected to slot [9980] located at 127.0.0.1:7001 "cluster4" #节点间来回重定向
到了这里，环境算是搭建好了。当然，这是最简单的集群了。以后随着演练的深入，也会对集群进行深入探讨。
遇到问题
可能遇到的错误（是第二次建立集群时报错）
ERR Slot 2217 is already busy (Redis::CommandError)
解决方法： (in all nodes did FLUSHALL and then CLUSTER RESET SOFT)
Either the node already knows other nodes
[root@hadoop2 cluster-test]# ./redis-trib.rb create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002
>>> Creating cluster
[ERR] Node 127.0.0.1:7000 is not empty. Either the node already knows other nodes (check with CLUSTER NODES) or contains some key in database 0.
解决方法：这是因为重复设置集群。
重启集群，发现数据丢失
集群创建完成后，当关机或者关闭集群再次启动的时候，一定要在node-conf所在的目录启动各个节点，
集群才能正常连接。
参考资源
http://blog.csdn.net/c77_cn/article/details/38227797
http://redis.io/topics/cluster-tutorial
http://redisdoc.com/topic/cluster-tutorial.html
