简介

　　为何要搭建Redis集群？Redis是在内存中保存数据的，而我们的电脑一般内存都不大，这也就意味着Redis不适合存储大数据，适合存储大数据的是Hadoop生态系统的Hbase或者是MogoDB。Redis更适合处理高并发，一台设备的存储能力是很有限的，但是多台设备协同合作，就可以让内存增大很多倍，这就需要用到集群。

　　Redis集群搭建的方式有多种，例如使用客户端分片、Twemproxy、Codis等，但从redis 3.0之后版本支持redis-cluster集群，它是Redis官方提出的解决方案，Redis-Cluster采用无中心结构，每个节点保存数据和整个集群状态,每个节点都和其他所有节点连接。其redis-cluster架构图如下：

客户端与 redis 节点直连,不需要中间 proxy 层.客户端不需要连接集群所有节点,连接集群中任何一个可用节点即可。

所有的 redis 节点彼此互联(PING-PONG 机制),内部使用二进制协议优化传输速度和带宽.

解决的问题：

• 1、单击版redis内存容量有限的问题
• 2、高并发场景下，单击版redis性能不高
• 3、单击版redis不具有高可用性，不能应用于生产环境

分布存储机制-槽

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1，redis-cluster 把所有的物理节点映射到[0-16383]slot 上,cluster 负责维护

node<->slot<->value

2，Redis 集群中内置了 16384 个哈希槽，当需要在 Redis 集群中放置一个 key-value 时，redis 先对 key 使用 crc16 算法算出一个结果，然后把结果对 16384 求余数，这样每个key 都会对应一个编号在 0-16383 之间的哈希槽，redis 会根据节点数量大致均等的将哈希槽映射到不同的节点。

例如三个节点：槽分布的值如下：

• SERVER1:  0-5460
• SERVER2:  5461-10922
• SERVER3:  10923-16383

键到slot的映射算法：HASH_SLOT=CRC16(key)mod16384

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容错机制-投票

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1，选举过程是集群中所有master参与,如果半数以上master节点与故障节点通信超过(cluster-node-timeout),认为该节点故障，自动触发故障转移操作.  故障节点对应的从节点自动升级为主节点

2，什么时候整个集群不可用(cluster_state:fail)?

如果集群任意master挂掉,且当前master没有slave，集群进入fail状态,也可以理解成集群的slot映射[0-16383]不完整时进入fail状态.

搭建Redis-Cluster

　　redis cluster 为了保证数据的高可用性，加入了主从模式，一个主节点对应一个或多个从节点，主节点提供数据存取，从节点则是从主节点拉取数据备份，当这个主节点挂掉后，就会有这个从节点选取一个来充当主节点，从而保证集群不会挂掉。所以redis-cluster是需要至少6个redis组成，三个Master（主）A B C，三个Slave（从）A1 B1 C1。严格来说每个redis需要一台机器，但是一般6个reids使用3台机器也是可以的，只要A和A1，B和B1，C和C1不在同一台机器上即可。

伪集群（所有redis安装到同一台机器上）准备工作：

1，安装gcc，ruby

Redis 是 c 语言开发的。安装 redis 需要 c 语言的编译环境。如果没有 gcc 需要在线安装。

yum install gcc-c++

使用yum命令安装 ruby  （我们需要使用ruby脚本来实现集群搭建）

yum install ruby

yum install rubygems

2，把文件放到服务器上并解压

mkdir redis-cluster

cd /usr/local/redis-cluster/

rz  上传redis的安装包

tar -zxvf redis-3.0.0.tar.gz

3，编译redis

cd /usr/local/redis-cluster/redis-3.0.0

make

4，安装6个reids实例

cd /usr/local/redis-cluster/redis-3.0.0

make install PREFIX=/usr/local/redis-cluster/redis-1

make install PREFIX=/usr/local/redis-cluster/redis-2

make install PREFIX=/usr/local/redis-cluster/redis-3

make install PREFIX=/usr/local/redis-cluster/redis-4

make install PREFIX=/usr/local/redis-cluster/redis-5

make install PREFIX=/usr/local/redis-cluster/redis-6

5，复制redis配置文件到6个redis实例中

cd /usr/local/redis-cluster/redis-3.0.0

cp redis.conf /usr/local/redis-cluster/redis-1/bin/

cp redis.conf /usr/local/redis-cluster/redis-2/bin/

cp redis.conf /usr/local/redis-cluster/redis-3/bin/

cp redis.conf /usr/local/redis-cluster/redis-4/bin/

cp redis.conf /usr/local/redis-cluster/redis-5/bin/

cp redis.conf /usr/local/redis-cluster/redis-6/bin/

配置集群

1，修改每个redis实例的配置文件，修改端口以及开启集群能力

vi /usr/local/redis-cluster/redis-1/bin/redis.conf

daemonize yes   后台运行

port 7001        redis实例的端口号

cluster-enabled yes  开启集群能力

vi /usr/local/redis-cluster/redis-2/bin/redis.conf

daemonize yes   后台运行

port 7002        redis实例的端口号

cluster-enabled yes  开启集群能力

vi /usr/local/redis-cluster/redis-3/bin/redis.conf

daemonize yes   后台运行

port 7003        redis实例的端口号

cluster-enabled yes  开启集群能力

vi /usr/local/redis-cluster/redis-4/bin/redis.conf

daemonize yes   后台运行

port 7004        redis实例的端口号

cluster-enabled yes  开启集群能力

vi /usr/local/redis-cluster/redis-5/bin/redis.conf

daemonize yes   后台运行

port 7005        redis实例的端口号

cluster-enabled yes  开启集群能力

vi /usr/local/redis-cluster/redis-6/bin/redis.conf

daemonize yes   后台运行

port 7006        redis实例的端口号

cluster-enabled yes  开启集群能力

2，启动6个redis实例

cd /usr/local/redis-cluster/redis-1/bin/

./redis-server redis.conf

cd /usr/local/redis-cluster/redis-2/bin/

./redis-server redis.conf

cd /usr/local/redis-cluster/redis-3/bin/

./redis-server redis.conf

cd /usr/local/redis-cluster/redis-4/bin/

./redis-server redis.conf

cd /usr/local/redis-cluster/redis-5/bin/

./redis-server redis.conf

cd /usr/local/redis-cluster/redis-6/bin/

./redis-server redis.conf

3，安装ruby用户搭建redis集群的脚本

cd /usr/local/redis-cluster

rz   上传redis-3.0.0.gem

gem install redis-3.0.0.gem

4，使用ruby脚本搭建redis集群(每个reids保证启动状态)

cd /usr/local/redis-cluster/redis-3.0.0/src

./redis-trib.rb create --replicas 1 192.168.127.137:7001 192.168.127.137:7002 192.168.127.137:7003 192.168.127.137:7004 192.168.127.137:7005 192.168.127.137:7006

>>> Creating cluster

Connecting to node 192.168.25.140:7001: OK

Connecting to node 192.168.25.140:7002: OK

Connecting to node 192.168.25.140:7003: OK

Connecting to node 192.168.25.140:7004: OK

Connecting to node 192.168.25.140:7005: OK

Connecting to node 192.168.25.140:7006: OK

>>> Performing hash slots allocation on 6 nodes...

Using 3 masters:

192.168.25.140:7001

192.168.25.140:7002

192.168.25.140:7003

Adding replica 192.168.25.140:7004 to 192.168.25.140:7001

Adding replica 192.168.25.140:7005 to 192.168.25.140:7002

Adding replica 192.168.25.140:7006 to 192.168.25.140:7003

M: 1800237a743c2aa918ade045a28128448c6ce689 192.168.25.140:7001

   slots:0-5460 (5461 slots) master

M: 7cb3f7d5c60bfbd3ab28800f8fd3bf6de005bf0d 192.168.25.140:7002

   slots:5461-10922 (5462 slots) master

M: 436e88ec323a2f8bb08bf09f7df07cc7909fcf81 192.168.25.140:7003

   slots:10923-16383 (5461 slots) master

S: c2a39a94b5f41532cd83bf6643e98fc277c2f441 192.168.25.140:7004

   replicates 1800237a743c2aa918ade045a28128448c6ce689

S: b0e38d80273515c84b1a01820d8ecee04547d776 192.168.25.140:7005

   replicates 7cb3f7d5c60bfbd3ab28800f8fd3bf6de005bf0d

S: 03bf6bd7e3e6eece5a02043224497c2c8e185132 192.168.25.140:7006

   replicates 436e88ec323a2f8bb08bf09f7df07cc7909fcf81

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 192.168.25.140:7001)

M: 1800237a743c2aa918ade045a28128448c6ce689 192.168.25.140:7001

   slots:0-5460 (5461 slots) master

M: 7cb3f7d5c60bfbd3ab28800f8fd3bf6de005bf0d 192.168.25.140:7002

   slots:5461-10922 (5462 slots) master

M: 436e88ec323a2f8bb08bf09f7df07cc7909fcf81 192.168.25.140:7003

   slots:10923-16383 (5461 slots) master

M: c2a39a94b5f41532cd83bf6643e98fc277c2f441 192.168.25.140:7004

   slots: (0 slots) master

   replicates 1800237a743c2aa918ade045a28128448c6ce689

M: b0e38d80273515c84b1a01820d8ecee04547d776 192.168.25.140:7005

   slots: (0 slots) master

   replicates 7cb3f7d5c60bfbd3ab28800f8fd3bf6de005bf0d

M: 03bf6bd7e3e6eece5a02043224497c2c8e185132 192.168.25.140:7006

   slots: (0 slots) master

   replicates 436e88ec323a2f8bb08bf09f7df07cc7909fcf81

[OK] All nodes agree about slots configuration.

>>> Check for open slots...

>>> Check slots coverage...

[OK] All 16384 slots covered.

5，向集群中添加数据

cd /usr/local/redis-cluster/redis-1/bin

./redis-cli -h 192.168.127.137 -p 7001 –c

set name abc

get name 

后续补充:(向集群中添加新节点、master、slave、指定master的slave)

添加master 前面是新添加的redis 后面是原来集群中的任意一个redis节点

./redis-trib.rb add-node 193.168.10.103:7000 193.168.10.101:7000

添加slave

./redis-trib.rb add-node --slave 193.168.10.103:7000 193.168.10.102:7001

//为哪个master添加slave(master-id be4a31b6fcab6295dd14799b3b67ec128fbbd7f9 为masterid)

./redis-trib.rb add-node --slave --master-id be4a31b6fcab6295dd14799b3b67ec128fbbd7f9 193.168.10.103:7000 193.168.10.102:7001

ps:

添加或者删除节 需要考虑redis的槽的问题，保证槽不丢失，每个master上都分配一定的槽

一个集群中一共有16383个槽，里面是redis的数据，这个要分配好了。

可使用以下命令重新分配槽：

./redis-trib.rb reshard 193.168.10.101:7000

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