Redis 虚拟IP切换

在sentinel进行切换时还会自动调用一个脚本（如果设置的话），做一些自动化操作，比如如果我们需要一个虚拟IP永远飘在Master上（这个VIP可不是被应用用来连接redis 的，用过的人都知道连接redis sentinel并不依赖于VIP的），那么可以在sentinel配置文件中配置：

sentinel client-reconfig-script mymaster /redis/script/failover.sh

在发生主从切换，Master发生变化时，该脚本会被sentinel进行调用，调用的参数如其配置文件所描述的：

# The following arguments are passed to the script:
#
# <master-name> <role> <state> <from-ip> <from-port> <to-ip> <to-port>
#
# <state> is currently always "failover"
# <role> is either "leader" or "observer"
# 
# The arguments from-ip, from-port, to-ip, to-port are used to communicate
# the old address of the master and the new address of the elected slave
# (now a master).

因此，我们可以在failover.sh中进行判断，如果该脚本所运行的主机IP等于新的Master IP，那么将VIP加上，如果不等于，则该机器为Slave，就去掉VIP。通过这种方式进行VIP的切换：

#!/bin/sh
_DEBUG="on"
DEBUGFILE=/tmp/sentinel_failover.log
VIP='192.168.2.120'
MASTERIP=${6}
MASK='24'
IFACE='eno33554960'
MYIP=$(ip -4 -o addr show dev ${IFACE}| grep -v secondary| awk '{split($4,a,"/");print a[1]}')

DEBUG () {
        if [ "$_DEBUG" = "on" ]; then
                echo `$@` >>  ${DEBUGFILE}
        fi
}

set -e
DEBUG date 
DEBUG echo $@  
DEBUG echo "Master: ${MASTERIP} My IP: ${MYIP}"
if [ ${MASTERIP} = ${MYIP} ]; then
        if [ $(ip addr show ${IFACE} | grep ${VIP} | wc -l) = 0 ]; then
                /sbin/ip addr add ${VIP}/${MASK} dev ${IFACE}
        DEBUG date
                DEBUG echo "/sbin/ip addr add ${VIP}/${MASK} dev ${IFACE}"
        DEBUG date
        DEBUG echo "IP Arp cleaning: /usr/sbin/arping -q -f -c 1 -A ${VIP} -I ${IFACE}" 
                /usr/sbin/arping -q -f -c 1 -A ${VIP} -I ${IFACE}
        DEBUG date 
        DEBUG echo "IP Failover finished!"
        fi
        exit 0
else
        if [ $(ip addr show ${IFACE} | grep ${VIP} | wc -l) != 0 ]; then
                /sbin/ip addr del ${VIP}/${MASK} dev ${IFACE}
                DEBUG echo "/sbin/ip addr del ${VIP}/${MASK} dev ${IFACE}"
        fi
        exit 0
fi
exit 1

最早这样的用法是一个日本人写的blog，请参见：http://blog.youyo.info/blog/2014/05/24/redis-cluster/