MySQL的高可用方案一般有如下几种：
keepalived+双主，MHA，MMM，Heartbeat+DRBD，PXC，Galera Cluster
比较常用的是keepalived+双主，MHA和PXC。
对于小公司，一般推荐使用keepalived+双主，简单。
下面来部署一下
配置环境：
角色 主机IP 主机名 操作系统版本 软件版本
VIP 192.168.244.10
master1 192.168.244.145 master1 CentOS7.1 MySQL 5.6.26，Keepalived v1.2.13
master2 192.168.244.146 master2 CentOS7.1 MySQL 5.6.26，Keepalived v1.2.13
一、 配置MySQL双主复制环境
1. 修改配置文件
master1中有关复制的配置如下：
[mysqld] log-bin=mysql-bin server-id=1 log_slave_updates=1
master2
[mysqld] log-bin=mysql-bin server-id=2 log_slave_updates=1 read_only=1
2. 创建复制用户
master1中创建：
CREATE USER 'repl'@'192.168.244.146' IDENTIFIED BY 'mysql'; GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.244.146';
master2中创建：
CREATE USER 'repl'@'192.168.244.145' IDENTIFIED BY 'mysql'; GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.244.145';
3. 执行CHANGE MASTER TO语句
因是从头搭建MySQL主从复制集群，所以不需要获取全局读锁来得到二进制日志文件的位置，直接根据show master status的输出来确认。
master1上执行：
CHANGE MASTER TO MASTER_HOST='192.168.244.146', MASTER_USER='repl', MASTER_PASSWORD='mysql', MASTER_LOG_FILE='mysql-bin.000004', MASTER_LOG_POS=64729;
master2上执行：
CHANGE MASTER TO MASTER_HOST='192.168.244.145', MASTER_USER='repl', MASTER_PASSWORD='mysql', MASTER_LOG_FILE='mysql-bin.000003', MASTER_LOG_POS=68479;
4. 分别在两个节点上执行start slave语句并通过show slave statusG查看复制是否搭建成功。
成功标准：
Slave_IO_Running: Yes Slave_SQL_Running: Yes
二、 配置Keepalived
1. 安装Keepalived
# yum install -y keepalived
当然，也可直接编译官方的源码包。
2. 修改Keepalived的配置文件
master1
[root@master1 ~]# vim /etc/keepalived/keepalived.conf
vrrp_script chk_mysql {
script "/etc/keepalived/check_mysql.sh"
interval 30 #设置检查间隔时长，可根据自己的需求自行设定
}
vrrp_instance VI_1 {
state BACKUP #通过下面的priority来区分MASTER和BACKUP，也只有如此，底下的nopreempt才有效
interface eno16777736
virtual_router_id 51
priority 100
advert_int 1
nopreempt #防止切换到从库后，主keepalived恢复后自动切换回主库
authentication {
auth_type PASS
auth_pass 1111
}
track_script {
chk_mysql
}
virtual_ipaddress {
192.168.244.10/24
}
}
关于keepalived的参数的详细介绍，可参考：LVS+Keepalived搭建MyCAT高可用负载均衡集群
其中，/etc/keepalived/check_mysql.sh内容如下：
#!/bin/bash
###判断如果上次检查的脚本还没执行完，则退出此次执行
if [ `ps -ef|grep -w "$0"|grep -v "grep"|wc -l` -gt 2 ];then
exit 0
fi
mysql_con='mysql -uroot -p123456'
error_log="/etc/keepalived/logs/check_mysql.err"
###定义一个简单判断mysql是否可用的函数
function excute_query {
${mysql_con} -e "select 1;" 2>> ${error_log}
}
###定义无法执行查询，且mysql服务异常时的处理函数
function service_error {
echo -e "`date "+%F %H:%M:%S"` -----mysql service error，now stop keepalived-----" >> ${error_log}
service keepalived stop &>> ${error_log}
echo "DB1 keepalived 已停止"|mail -s "DB1 keepalived 已停止,请及时处理！" slowtech@126.com 2>> ${error_log}
echo -e "
---------------------------------------------------------
" >> ${error_log}
}
###定义无法执行查询,但mysql服务正常的处理函数
function query_error {
echo -e "`date "+%F %H:%M:%S"` -----query error, but mysql service ok, retry after 30s-----" >> ${error_log}
sleep 30
excute_query
if [ $? -ne 0 ];then
echo -e "`date "+%F %H:%M:%S"` -----still can't execute query-----" >> ${error_log}
###对DB1设置read_only属性
echo -e "`date "+%F %H:%M:%S"` -----set read_only = 1 on DB1-----" >> ${error_log}
mysql_con -e "set global read_only = 1;" 2>> ${error_log}
###kill掉当前客户端连接
echo -e "`date "+%F %H:%M:%S"` -----kill current client thread-----" >> ${error_log}
rm -f /tmp/kill.sql &>/dev/null
###这里其实是一个批量kill线程的小技巧
mysql_con -e 'select concat("kill ",id,";") from information_schema.PROCESSLIST where command="Query" or command="Execute" into outfile "/tmp/kill.sql";'
mysql_con -e "source /tmp/kill.sql"
sleep 2 ###给kill一个执行和缓冲时间
###关闭本机keepalived
echo -e "`date "+%F %H:%M:%S"` -----stop keepalived-----" >> ${error_log}
service keepalived stop &>> ${error_log}
echo "DB1 keepalived 已停止"|mail -s "DB1 keepalived 已停止,请及时处理！" slowtech@126.com 2>> ${error_log}
echo -e "
---------------------------------------------------------
" >> ${error_log}
else
echo -e "`date "+%F %H:%M:%S"` -----query ok after 30s-----" >> ${error_log}
echo -e "
---------------------------------------------------------
" >> ${error_log}
fi
}
###检查开始: 执行查询
excute_query
if [ $? -ne 0 ];then
service mysqld status &>/dev/null
if [ $? -ne 0 ];then
service_error
else
query_error
fi
fi
通过具体的查询语句来判断数据库服务的可用性，如果查询失败，则判断mysqld进程本身的状态，如果不正常，则直接停止当前节点的keepalived，将VIP转移到另外一个节点，如果正常，则等待30s，再次执行查询语句，还是失败，则将当前的master节点设置为read_only，并kill掉当前的客户端连接，然后停止当前的keepalived。
master2
[root@master2 ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalived
vrrp_instance VI_1 {
state BACKUP
interface eno16777736
virtual_router_id 51
priority 90
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
notify_master /etc/keepalived/notify_master_mysql.sh #此条指令告诉keepalived发现自己转为MASTER后执行的脚本
virtual_ipaddress {
192.168.244.10/24
}
}
其中，/etc/keepalived/notify_master_mysql.sh的内容如下：
#!/bin/bash
###当keepalived监测到本机转为MASTER状态时，执行该脚本
change_log=/etc/keepalived/logs/state_change.log
mysql_con='mysql -uroot -p123456'
echo -e "`date "+%F %H:%M:%S"` -----keepalived change to MASTER-----" >> $change_log
slave_info() {
###统一定义一个函数取得slave的position、running、和log_file等信息
###根据函数后面所跟参数来决定取得哪些数据
if [ $1 = slave_status ];then
slave_stat=`${mysql_con} -e "show slave statusG;"|egrep -w "Slave_IO_Running|Slave_SQL_Running"`
Slave_IO_Running=`echo $slave_stat|awk '{print $2}'`
Slave_SQL_Running=`echo $slave_stat|awk '{print $4}'`
elif [ $1 = log_file -a $2 = pos ];then
log_file_pos=`${mysql_con} -e "show slave statusG;"|egrep -w "Master_Log_File|Read_Master_Log_Pos|Relay_Master_Log_File|Exec_Master_Log_Pos"`
Master_Log_File=`echo $log_file_pos|awk '{print $2}'`
Read_Master_Log_Pos=`echo $log_file_pos|awk '{print $4}'`
Relay_Master_Log_File=`echo $log_file_pos|awk '{print $6}'`
Exec_Master_Log_Pos=`echo $log_file_pos|awk '{print $8}'`
fi
}
action() {
###经判断'应该&可以'切换时执行的动作
echo -e "`date "+%F %H:%M:%S"` -----set read_only = 0 on DB2-----" >> $change_log
###解除read_only属性
${mysql_con} -e "set global read_only = 0;" 2>> $change_log
echo "DB2 keepalived转为MASTER状态，线上数据库切换至DB2"|mail -s "DB2 keepalived change to MASTER"
slowtech@126.com 2>> $change_log
echo -e "---------------------------------------------------------
" >> $change_log
}
slave_info slave_status
if [ $Slave_SQL_Running = Yes ];then
i=0 #一个计数器
slave_info log_file pos
###判断从master接收到的binlog是否全部在本地执行(这样仍无法完全确定从库已追上主库，因为无法完全保证io_thread没有延时(由网络传输问题导致的从库落后的概率很小)
until [ $Master_Log_File = $Relay_Master_Log_File -a $Read_Master_Log_Pos = $Exec_Master_Log_Pos ]
do
if [ $i -lt 10 ];then #将等待exec_pos追上read_pos的时间限制为10s
echo -e "`date "+%F %H:%M:%S"` -----Relay_Master_Log_File=$Relay_Master_Log_File,Exec_Master_Log_Pos=$Exec_Master_Log_Pos is behind Master_Log_File=$Master_Log_File,Read_Master_Log_Pos=$Read_Master_Log_Pos, wait......" >> $change_log #输出消息到日志，等待exec_pos=read_pos
i=$(($i+1))
sleep 1
slave_info log_file pos
else
echo -e "The waits time is more than 10s,now force change. Master_Log_File=$Master_Log_File Read_Master_Log_Pos=$Read_Master_Log_Pos Relay_Master_Log_File=$Relay_Master_Log_File Exec_Master_Log_Pos=$Exec_Master_Log_Pos" >> $change_log
action
exit 0
fi
done
action
else
slave_info log_file pos
echo -e "DB2's slave status is wrong,now force change. Master_Log_File=$Master_Log_File Read_Master_Log_Pos=$Read_Master_Log_Pos Relay_Master_Log_File=$Relay_Master_Log_File Exec_Master_Log_Pos=$Exec_Master_Log_Pos" >> $change_log
action
fi
整个脚本的逻辑是让从的Exec_Master_Log_Pos尽可能的追上Read_Master_Log_Pos，它给了10s的限制，如果还是没有追上，则直接将master2设置为主（通过解除read_only属性），其实这里面还是有待商榷的，譬如10s的限制是否合理，还是一定需要Exec_Master_Log_Pos=Read_Master_Log_Pos才切换。
当原主恢复正常后，如何将VIP从master2切回到master1中呢？
#!/bin/bash
###手动执行将主库切换回DB1的操作
mysql_con='mysql -uroot -p123456'
echo -e "`date "+%F %H:%M:%S"` -----change to BACKUP manually-----" >> /etc/keepalived/logs/state_change.log
echo -e "`date "+%F %H:%M:%S"` -----set read_only = 1 on DB2-----" >> /etc/keepalived/logs/state_change.log
$mysql_con -e "set global read_only = 1;" 2>> /etc/keepalived/logs/state_change.log
###kill掉当前客户端连接
echo -e "`date "+%F %H:%M:%S"` -----kill current client thread-----" >> /etc/keepalived/logs/state_change.log
rm -f /tmp/kill.sql &>/dev/null
###这里其实是一个批量kill线程的小技巧
$mysql_con -e 'select concat("kill ",id,";") from information_schema.PROCESSLIST where command="Query" or command="Execute" into outfile "/tmp/kill.sql";'
$mysql_con -e "source /tmp/kill.sql" 2>> /etc/keepalived/logs/state_change.log
sleep 2 ###给kill一个执行和缓冲时间
###确保DB1已经追上了,下面的repl为复制所用的账户，-h后跟DB1的内网IP
log_file_pos=`mysql -urepl -pmysql -h192.168.244.145 -e "show slave statusG;"|egrep -w "Master_Log_File|Read_Master_Log_Pos|Relay_Master_Log_File|Exec_Master_Log_Pos"`
Master_Log_File=`echo $log_file_pos|awk '{print $2}'`
Read_Master_Log_Pos=`echo $log_file_pos|awk '{print $4}'`
Relay_Master_Log_File=`echo $log_file_pos|awk '{print $6}'`
Exec_Master_Log_Pos=`echo $log_file_pos|awk '{print $8}'`
until [ $Read_Master_Log_Pos = $Exec_Master_Log_Pos -a $Master_Log_File = $Relay_Master_Log_File ]
do
echo -e "`date "+%F %H:%M:%S"` -----DB1 Exec_Master_Log_Pos($exec_pos) is behind Read_Master_Log_Pos($read_pos), wait......" >> /etc/keepalived/logs/state_change.log
sleep 1
done
###然后解除DB1的read_only属性
echo -e "`date "+%F %H:%M:%S"` -----set read_only = 0 on DB1-----" >> /etc/keepalived/logs/state_change.log
ssh 192.168.244.145 'mysql -uroot -p123456 -e "set global read_only = 0;" && /etc/init.d/keepalived start' 2>> /etc/keepalived/logs/state_change.log
###重启DB2的keepalived使VIP漂移到DB1
echo -e "`date "+%F %H:%M:%S"` -----make VIP move to DB1-----" >> /etc/keepalived/logs/state_change.log
/sbin/service keepalived restart &>> /etc/keepalived/logs/state_change.log
echo "DB2 keepalived转为BACKUP状态，线上数据库切换至DB1"|mail -s "DB2 keepalived change to BACKUP" slowtech@126.com 2>> /etc/keepalived/logs/state_change.log
echo -e "--------------------------------------------------
" >> /etc/keepalived/logs/state_change.log
总结：
1. /etc/keepalived/check_mysql.sh和/etc/keepalived/notify_master_mysql.sh必须加可执行权限。
如果前者没有加可执行权限，则master1上将不会绑定VIP，日志直接提示如下信息：
May 25 14:37:09 master1 Keepalived_vrrp[3165]: VRRP_Instance(VI_1) Entering BACKUP STATE May 25 14:37:09 master1 Keepalived_vrrp[3165]: VRRP sockpool: [ifindex(2), proto(112), unicast(0), fd(10,11)] May 25 14:37:50 master1 Keepalived_vrrp[3165]: VRRP_Instance(VI_1) Now in FAULT state
2. 在Keepalived中有两种模式，分别是master->backup模式和backup->backup模式，这两种模式有什么区别呢？
在master->backup模式下，一旦主库宕掉，虚拟IP会自动漂移到从库，当主库修复后，keepalived启动后，还会把虚拟IP抢过来，即使你设置nopreempt（不抢占）的方式抢占IP的动作也会发生。在backup->backup模式下，当主库宕掉后虚拟IP会自动漂移到从库上，当原主恢复之后重启keepalived服务，并不会抢占新主的虚拟IP，即使是优先级高于从库的优先级别，也不会抢占IP。为了减少IP的漂移次数，生产中我们通常是把修复好的主库当做新主库的备库。
3. 本文是在MySQL主库高可用 -- 双主单活故障自动切换方案 基础上，结合自己对于MySQL的理解整理的。原文的脚本直接执行有点问题，思路有有点瑕疵，于是结合自己的实际环境，重新修改了一把。
4. 在测试的过程中，有以下几点需要注意：
1> master1检测脚本的逻辑是如果MySQL的服务不可用，则通过service keepalived stop命令来关闭keepalived，但在实际测试的过程中，却出现了即便执行了service keepalived stop命令，keepalived进程依然没有停止，导致MySQL的服务虽然不可用了，但VIP并不没有漂移到master2上。
优化方案：在执行service keepalived stop后，等待5s，再次检测keepalived的状态，如果keepalived没有关闭，则直接kill掉。
2> keepalived的日志默认是输出到/var/log/messages中，这样不便于查看。如何自定义keepalived的日志输出文件呢？
如果是用service启动的，修改/etc/sysconfig/keepalived文件
KEEPALIVED_OPTIONS="-D -d -S 0"
如果不是，则启动的时候指定以上参数，如：
/usr/local/keepalived/sbin/keepalived -d -D -S 0
修改/etc/syslog.conf
# keepalived -S 0 local0.* /var/log/keepalived.log
重启syslog
RHEL 5&6：service syslog restart
RHEL 7：service rsyslog restart