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。
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编译
make
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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
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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
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3.建立3个cluster 节点对应的redis.conf文件
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[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
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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）
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cd
7000
.
/redis-server
.
/redis
.conf
cd
..
/7001/
.
/redis-server
.
/redis
.conf
cd
..
/7002
.
/redis-server
.
/redis
.conf
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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
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.
/redis-trib
.rb create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002
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[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
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[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
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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。
本文转自 randy_shandong 51CTO博客，原文链接：http://blog.51cto.com/dba10g/1851458，如需转载请自行联系原作者
