Mysql - 高可用方案之MM+Keepalived

一、概述

本文将介绍mysql的MM+Keepalived方案。该方案由两个mysql服务器组成，这两个mysql互为主备。其中一台主作为写服务器，另一台主作为读服务器。通过keepalived软件管理写vip，当承担写服务器的mysql出现故障时，将写vip漂移到读服务器上，实现高可用。

二、节点介绍

本次实验采用2台虚拟机，操作系统版本Centos6.10，mysql版本5.7.25

node1    10.40.16.61  主库  提供写服务

node2    10.40.16.62  主库  提供读服务

还须预留1个vip，现在不用配置，这里先提一下，后面的安装步骤用得到

10.40.16.71  写vip

三、安装

1. 配置双主架构

安利一个自己写的mysql一键安装脚本

mysql搭建完成后，就可以配置互为主备的架构了。

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这样node1和node2就互为主备了

在node2上将数据库设置为只读模式

(root@localhost)[(none)]> set global read_only = 1;

2. 安装keepalive软件

node1&node2:

yum install -y keepalived

四、修改配置文件

1. node1

编辑配置文件/etc/keepalived/keepalived.conf

! Configuration File for keepalived

vrrp_script chk_mysql {
    script "/etc/keepalived/check_mysql.sh" # 自定义检查脚本
    interval 30                             # 设置检查间隔时长，可自行设定
}

vrrp_instance VI_1 {
    state BACKUP                            # BACKUP状态，具体意思后面介绍
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    nopreempt                               # 防止主库切换到从库后，主库恢复后自动切换回主库
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    track_script {
        chk_mysql
    }
    virtual_ipaddress {
        10.40.16.71/24                      # vip
    }
}

编辑检查mysql主库的脚本文件/etc/keepalived/check_mysql.sh

#!/bin/bash
source /root/.bash_profile
###填数据库相关信息###
DB_USER='root'
DB_PASSWD='root'
U_EMAIL='[e-mail]'
######################

###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 "$0" | grep -v "grep" | wc -l` -gt 2 ]; then
    exit 0
fi
mysql_con="mysql -u$DB_USER -p$DB_PASSWD"
error_log="/etc/keepalived/logs/check_mysql.err"

###如果error_log目录不存在则创建目录
if [ -d /etc/keepalived/logs ]; then
    usleep
else
    mkdir -p /etc/keepalived/logs
fi

###定义一个简单判断mysql是否可用的函数
function execute_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 2>&1
    echo "master1 keepalived stopped" | mail -s "master1 keepalived stopped, please take notice!" $U_EMAIL 2>> $error_log
    echo -e "\n---------------------------------------------------------\n" >> $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
    execute_query
    if [ $? -ne 0 ]; then
        echo -e "`date "+%F %H:%M:%S"`    ----still can't execute query----" >> $error_log

        ###关闭本机mysql
        echo -e "`date "+%F %H:%M:%S"`    ----stop mysql service----" >> $error_log
        service mysql stop &>> $error_log
        sleep 2    ###给执行和缓冲时间

        ###关闭本机keepalived
        echo -e "`date "+%F %H:%M:%S"`    ----stop keepalived----" >> $error_log
        service keepalived stop &>> $error_log
        echo "master1 keepalived stopped" | mail -s "master1 keepalived stopped, please take notice!" $U_EMAIL 2>> $error_log
        echo -e "\n---------------------------------------------------------\n" >> $error_log
    else
        echo -e "`date "+%F %H:%M:%S"`    ----query ok after 30s----" >> $error_log
        echo -e "\n---------------------------------------------------------\n" >> $error_log
    fi
}

###检查开始: 执行查询
execute_query
if [ $? -ne 0 ]; then
    service mysql status &> /dev/null
    if [ $? -ne 0 ]; then
        service_error
    else
        query_error
    fi
fi

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chmod +x /etc/keepalived/check_mysql.sh

该脚本的作用有两个

a. mysql进程挂掉了，直接关闭keepalived服务

b. mysql进程正常，但是无法执行查询，比如进程卡死了等等原因。则同时关闭mysql和keepalived

2. node2

编辑配置文件/etc/keepalived/keepalived.conf

! Configuration File for keepalived

vrrp_instance VI_1 {
    state BACKUP                # BACKUP状态，具体意思后面介绍
    interface eth0
    virtual_router_id 51
    priority 90                 # 优先级设置为90，这个值设置比节点1低
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    notify_master /etc/keepalived/notify_master_mysql.sh
    virtual_ipaddress {
        10.40.16.71/24          # vip
    }
}

编辑检查mysql从库的脚本文件/etc/keepalived/notify_master_mysql.sh

#!/bin/bash
source /root/.bash_profile
###当keepalived监测到本机转为MASTER状态时，执行该脚本
###填数据库相关信息###
DB_USER='root'
DB_PASSWD='root'
U_EMAIL='[e-mail]'
######################

change_log='/etc/keepalived/logs/state_change.log'
mysql_con="mysql -u$DB_USER -p$DB_PASSWD"
echo -e "`date "+%F %H:%M:%S"`    ----master2 keepalived change to MASTER----" >> $change_log

###如果error_log目录不存在则创建目录
if [ -d /etc/keepalived/logs ]; then
    usleep
else
    mkdir -p /etc/keepalived/logs
fi

slave_info() {
    ###检查从库状态
    slave_stat=`$mysql_con -e "show slave status\G"`
    Slave_IO_Running=`echo $slave_stat | egrep -w "Slave_IO_Running" | awk '{print $2}'`
    Slave_SQL_Running=`echo $slave_stat | egrep -w "Slave_SQL_Running" | awk '{print $2}'`
    Master_Log_File=`echo $slave_stat | egrep -w "Master_Log_File" | awk '{print $2}'`
    Read_Master_Log_Pos=`echo $slave_stat | egrep -w "Read_Master_Log_Pos" | awk '{print $2}'`
    Relay_Master_Log_File=`echo $slave_stat | egrep -w "Relay_Master_Log_File" | awk '{print $2}'`
    Exec_Master_Log_Pos=`echo $slave_stat | egrep -w "Exec_Master_Log_Pos" | awk '{print $2}'`
}

action() {
    ###解除read_only属性
    echo -e "`date "+%F %H:%M:%S"`    ----set read_only = 0 on master2----" >> $change_log
    $mysql_con -e "set global read_only = 0;" 2>> $change_log
    echo "master2 keepalived change to MASTER，线上数据库切换至master2" | mail -s "master2 keepalived change to MASTER" $U_EMAIL 2>> $change_log
    echo -e "---------------------------------------------------------\n" >> $change_log
}

slave_info
if [ $Slave_SQL_Running == 'Yes' ]; then
    i=0    #一个计数器
    ###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(但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 [ $i -lt 10 ]; then    #将等待exec_pos追上read_pos的时间限制为20s
            echo -e "`date "+%F %H:%M:%S"`    ----Relay_Master_Log_File=$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......" >> $change_log    #输出消息到日志，等待exec_pos=read_pos
            i=$(($i+1))
            sleep 2
            slave_info
        else
            echo -e "The waits time is more than 20s,now force change. Master_Log_File=$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" >> $change_log
            action
            exit 0
        fi
     done
    action
else
    echo -e "master2's slave status is not running,now force change. Master_Log_File=$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

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chmod +x /etc/keepalived/notify_master_mysql.sh

该脚本的作用有三个

a. slave sql线程没有运行，直接将从库只读关闭

c. slave sql线程正在运行，如果从库没有延迟，直接将从库只读关闭

b. slave sql线程正在运行，如果从库有延迟，等待一段时间(这个自己设置)再将从库只读关闭

这里解释下keepalived.conf的"state BACKUP"的意思，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，即使是原主优先级高于从库的优先级别，也不会抢占虚拟IP。

所以，为了减少虚拟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。因而采用backup->backup模式居多。

五、启动Keepailived

node1&node2:

service keepalived start

注意因为我们使用的是backup->backup模式，所以启动keepalived的顺序需要先启动node1，再启动node2，这样vip才会在node1上。如果先启动node2，再启动node1，node1并不会把虚拟IP抢过来。

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六、测试

1. 模拟主库宕机的情况

关闭node1的mysql数据库

service mysql stop

查看node1的keepalived日志/etc/keepalived/logs/check_mysql.err

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查看node1和node2的vip，发现vip已经转移到了node2

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node2的read_only参数也变成了off      

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node2的切换日志可以查看/etc/keepalived/logs/state_change.log

看看有没有收到邮件，呵呵:-)

failover正常！

2. 模拟主库正常，但是无法查询

重新打开node1的mysql数据库和keepalived服务

service mysql start

service keepalived start

重启node2的keepalived服务

service keepalived restart

在node2上将数据库设置为只读模式

(root@localhost)[(none)]> set global read_only = 1;

这样就跟最初的状态一致了，主库是node1，从库是node2，vip在node1上。

在node1上将参数max_connections设置得足够小

(root@localhost)[(none)]> set global max_connections = 2;

在node1上然后多开几个连接，直到出现无法连接的情况。以此来模拟无法查询的情况。

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查看node1的keepalived日志/etc/keepalived/logs/check_mysql.err

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查看node1，发现keepalived和mysql服务都已经停止

[root@mysqla ~]# service mysql status

MySQL is not running                                    

[root@mysqla ~]# service keepalived status

keepalived is stopped

node2的read_only参数也变成了off

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vip也已经漂移过来了

[root@mysqlb ~]# ip a

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failover正常！

七、手动切换

还有一个场景就是，如何手工切换。举个例子，node2目前是主库，但是node1通过各种办法修复好了，我想让node1当主库。

重启node1的mysql服务

service mysql restart

这样node2是主库，node1是备库，vip在node2上

在node2上创建手工切换的脚本vi /etc/keepalived/manual_switch_to_master

#!/bin/bash
source /root/.bash_profile
###在master2上手动执行将主库切换回master1的操作
###填数据库相关信息###
DB_USER='root'
DB_PASSWD='root'
U_EMAIL='[e-mail]'
MASTER1='10.40.16.61'
MASTER2='10.40.16.62'
REPL_USER='repl'
REPL_PASSWD='123456'
MASTER1_MYSQL_PATH='/usr/local/mysql/bin'
######################

###如果error_log目录不存在则创建目录
if [ -d /etc/keepalived/logs ]; then
    usleep
else
    mkdir -p /etc/keepalived/logs
fi

mysql_con="mysql -u$DB_USER -p$DB_PASSWD"

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 master2----" >> /etc/keepalived/logs/state_change.log
$mysql_con -e "set global read_only = 1;" >> /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
if [ -e /tmp/kill.sql ]; then
    rm -f /tmp/kill.sql &> /dev/null
fi
###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

slave_info() {
    ###检查从库状态
    slave_stat=`mysql -u$REPL_USER -p$REPL_PASSWD -h$MASTER1 -e "show slave status\G"`
    Master_Log_File=`echo $slave_stat | egrep -w "Master_Log_File" | awk '{print $2}'`
    Read_Master_Log_Pos=`echo $slave_stat | egrep -w "Read_Master_Log_Pos" | awk '{print $2}'`
    Relay_Master_Log_File=`echo $slave_stat | egrep -w "Relay_Master_Log_File" | awk '{print $2}'`
    Exec_Master_Log_Pos=`echo $slave_stat | egrep -w "Exec_Master_Log_Pos" | awk '{print $2}'`
}

slave_info
until [ $Read_Master_Log_Pos = $Exec_Master_Log_Pos -a $Master_Log_File = $Relay_Master_Log_File ]
do
    echo -e "`date "+%F %H:%M:%S"`    ----Relay_Master_Log_File=$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......" >> /etc/keepalived/logs/state_change.log
    sleep 2
    slave_info
done

###然后解除master1的read_only属性并打开keepalived服务
echo -e "`date "+%F %H:%M:%S"`    ----set read_only = 0 on master1----" >> /etc/keepalived/logs/state_change.log
ssh $MASTER1 "$MASTER1_MYSQL_PATH/mysql -u$DB_USER -p$DB_PASSWD -e 'set global read_only = 0;' && /etc/init.d/keepalived start" 2>> /etc/keepalived/logs/state_change.log

###重启master2的keepalived服务，使VIP漂移到master1
echo -e "`date "+%F %H:%M:%S"`    ----make VIP move to master1----" >> /etc/keepalived/logs/state_change.log
/etc/init.d/keepalived restart &>> /etc/keepalived/logs/state_change.log
echo "master2 keepalived restart，vip change to master1" | mail -s "master2 keepalived change to BACKUP" $U_EMAIL 2>> /etc/keepalived/logs/state_change.log
echo -e "\n--------------------------------------------------\n" >> /etc/keepalived/logs/state_change.log

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在node2上执行脚本

chmod +x /etc/keepalived/manual_switch_to_master

[root@mysqlb keepalived]# sh /etc/keepalived/manual_switch_to_master

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在node2上查看ip，发现vip不见了

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在node2上查看read_only参数

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在node1上查看vip，发现vip已经漂移过来了

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手工切换完成！

八、总结

mm+keepalive的配置简单，相对于传统的主从架构，能实现比较简单的写库故障转移。