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。

　　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 keepalived

global_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 keepalived

global_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：https://files.cnblogs.com/lulu/scripts.rar