使用keepalived 实现redis主从高可用

keepalived官方有中文文档：LVS + Keepalived Chinese application doc - March 16, 2010。

　　keepalived 实现VRRP协议，从路由级别实现VIP切换，可以完全避免类似heartbeat 脑裂问题。可以很nice的实现主从、主备、互备方案，尤其是无状态业务，有状态业务就需要额外花些功夫了。

     既然mysql 可以使用keepalived很好的做到主从切换，redis自然也就有样学样就成了。

 

　　redis主从实现完全没有mysql成熟，仅仅是可用而已，按照作者规划相应改进需要等3.0以后了。经过测试主从也不是那么完全不靠谱。主要问题在于同步连接断开之后需要重新全量同步，如果频繁进行会对主服务带来很大性能影响。 但现实中主从机器往往要求放在一个机柜同一台交换设备下，网络闪断情况极低；再者主从同步在同步数量量大情况下，需要将缓存区调得足够大，不然也容易造成连接断开。

　　实现切换逻辑如下：A B两台机器

　　1. A 、B 依次启动，A作为主、B为从

　　2.主A 挂掉，B接管业务，作为主

　　3.A 起来，作为从SLAVEOF B

　　4.B 挂掉，A 切回主

　　将一台全部作为主，即可实现主从，可做读写分离；也可以一台机器上多个实例一半主、一半从，实现互备份，两机同时接管业务，一台宕机后业务都集中在一台上。

　  在keepalived 有两个角色：Master(一个)、Backup（多个），如果设置一个为Master，但Master挂了后再起来，必然再次业务又一次切换，这对于有状态服务是不可接受的。解决方案就是两台机器都设置为Backup，而且优先级高的Backup设置为nopreemt 不抢占。

 

 　　安装比较简单：

　　需要依赖包：openssl-devel（ubuntu 中为 libssl-dev),popt-devel （ubuntu中为libpopt-dev），redheat中都已经有了。

   1. 安装redis
　　　　
　　　　wget http://redis.googlecode.com/files/redis-2.0.0-rc4.tar.gz
tar zxvf redis-2.0.0-rc4.tar.gz
cd redis-2.0.0-rc4
make
cp redis.conf /etc/ 这个文件是redis启动的配置文件
cp redis-benchmark redis-cli redis-server /usr/bin/
　　　　redis-server /etc/redis.conf
　　　　redis-cli
　　　　注意修改配置：daemonize yes  

      2. 安装高可用软件 keepalived 
　
wget http://www.keepalived.org/software/keepalived-1.1.20.tar.gz
tar zxvf keepalived-1.1.20.tar.gz
cd keepalived-1.1.20
./configure --with-kernel-dir=/usr/src/kernels/2.6.18-128.el5-x86_64/ --disable-fwmark compile without SO_MARK support
make && make install

cp /usr/local/etc/rc.d/init.d/keepalived  /etc/rc.d/init.d/
cp /usr/local/etc/sysconfig/keepalived /etc/sysconfig/
mkdir /etc/keepalived
cp /usr/local/etc/keepalived/keepalived.conf  /etc/keepalived/
cp /usr/local/sbin/keepalived  /usr/sbin
/etc/init.d/keepalived start

　　配置文件默认路径：/etc/keepalived/keepalived.conf 也可以手动指定路径，不过要注意的是手动指定需要使用绝对路径。

　　使用keepalived -D 运行，即可启动3个守护进程：一个父进程，一个check健康检查，一个Vrrp，-D将日志写入/var/log/message 

 

　　配置如下：

   主：

! Configuration File for keepalivedglobal_defs {   router_id test}vrrp_script chk_redis {      script "/etc/keepalived/scripts/redis_check.sh 127.0.0.1 7001"      interval 2 
     timeout 2
     fall 3}vrrp_script chk_redis2 {      script "/etc/keepalived/scripts/redis_check.sh 127.0.0.1 7002"     interval 2
     timeout 2
     fall 3
}vrrp_instance redis {    state BACKUP # 主也配置为SLAVE    interface wlan0}      virtual_router_id 51     priority  150           nopreempt # 不抢占，注意加上    advert_int 1            authentication {           auth_type PASS           auth_pass lulu    }    virtual_ipaddress {      192.168.1.144    }    track_script {          chk_redis     }     notify_master "/etc/keepalived/scripts/redis_master_slave.sh 127.0.0.1 192.168.1.126 7001"    notify_backup "/etc/keepalived/scripts/redis_backup_slave.sh 127.0.0.1 192.168.1.126 7001"    notify_fault /etc/keepalived/scripts/redis_fault.sh     notify_stop /etc/keepalived/scripts/redis_stop.sh }vrrp_instance redis2 {    state BACKUP      interface wlan0 }      virtual_router_id 50     priority 150             advert_int 1             nopreempt    authentication {              auth_type PASS          auth_pass lulu    }    virtual_ipaddress {      192.168.1.145    }    track_script {          chk_redis2     }    notify_master "/etc/keepalived/scripts/redis_master_slave.sh 127.0.0.1 192.168.1.126 7002"    notify_backup "/etc/keepalived/scripts/redis_backup_slave.sh 127.0.0.1 192.168.1.126 7002"    notify_fault /etc/keepalived/scripts/redis_fault.sh     notify_stop /etc/keepalived/scripts/redis_stop.sh }

备：

! Configuration File for keepalivedglobal_defs {   router_id test}vrrp_script chk_redis {      script "/etc/keepalived/scripts/redis_check.sh 127.0.0.1 7001"      interval 2
     timeout 2
     fall 3}vrrp_script chk_redis2 {      script "/etc/keepalived/scripts/redis_check.sh 127.0.0.1 7002"      interval 2
     timeout 2
     fall 3}vrrp_instance redis {    state BACKUP       interface wlan0 }      virtual_router_id 51      priority  100           advert_int 1            authentication {            auth_type PASS           auth_pass test    }    virtual_ipaddress {     192.168.1.144    }    track_script {          chk_redis     }     notify_master "/etc/keepalived/scripts/redis_master_slave.sh 127.0.0.1 192.168.1.126 7001"    notify_backup "/etc/keepalived/scripts/redis_backup_slave.sh 127.0.0.1 192.168.1.126 7001"    notify_fault /etc/keepalived/scripts/redis_fault.sh     notify_stop /etc/keepalived/scripts/redis_stop.sh }vrrp_instance redis2 {    state BACKUP       interface wlan0 }      virtual_router_id 50      advert_int 1          priority 100    authentication {           auth_type PASS          auth_pass test    }    virtual_ipaddress {       192.168.1.145    }    track_script {          chk_redis2    }    notify_master "/etc/keepalived/scripts/redis_master_slave.sh 127.0.0.1 192.168.1.126 7002"    notify_backup "/etc/keepalived/scripts/redis_backup_slave.sh 127.0.0.1 192.168.1.126 7002"    notify_fault /etc/keepalived/scripts/redis_fault.sh     notify_stop /etc/keepalived/scripts/redis_stop.sh }

其他脚本见附件：http://files.cnblogs.com/lulu/scripts.rar