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：http://files.cnblogs.com/lulu/scripts.rar