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MySQL + Keepalived 实现双主单活高可用

　　我们通常说的双机热备是指两台机器都在运行，但并不是两台机器都同时在提供服务。当提供服务的一台出现故障的时候，另外一台会马上自动接管并且提供服务，而且切换的时间非常短。MySQL双主复制，即互为Master-Slave(只有一个Master提供写操作)，可以实现数据库服务器的热备，但是一个Master宕机后不能实现动态切换。使用Keepalived，可以通过虚拟IP，实现双主对外的统一接口以及自动检查、失败切换机制，从而实现MySQL数据库的高可用方案。

Keepalived 保持存活，也就是所谓的高可用或热备，用来防止单点故障（单点故障是指一旦某一点出现故障就会导致整个系统架构的不可用现象的发生，那说到keepalived必须提及一个协议VRRP协议，这个协议算是keepalived实现的基础。
1）Keepalived的工作原理是VRRP（Virtual Router Redundancy Protocol）虚拟路由冗余协议。在VRRP中有两组重要的概念：VRRP路由器和虚拟路由器，主控路由器和备份路由器。
2）VRRP路由器是指运行VRRP的路由器，是物理实体，虚拟路由器是指VRRP协议创建的，是逻辑概念。一组VRRP路由器协同工作，共同构成一台虚拟路由器。
Vrrp中存在着一种选举机制，用以选出提供服务的路由即主控路由，其他的则成了备份路由。当主控路由失效后，备份路由中会重新选举出一个主控路由，来继续工作，来保障不间断服务。

过多内容在这里就不做详细介绍了，下面记录下Mysql+Keepalived双主热备的高可用方案的操作记录

1）先实施Master->Slave的主主同步。主主是数据双向同步，主从是数据单向同步。一般情况下，主库宕机后，需要手动将连接切换到从库上。（但是用keepalived就可以自动切换）
2）再结合Keepalived的使用，通过VIP实现Mysql双主对外连接的统一接口。即客户端通过Vip连接数据库；当其中一台宕机后，VIP会漂移到另一台上，这个过程对于客户端的数据连接来说几乎无感觉，从而实现高可用。

环境描述：
mysql的安装可以参考：https://www.cnblogs.com/Camiluo/p/9923030.html
Centos7.6版本
Master1：192.168.49.13        安装mysql和keepalived
Master2: 192.168.49.128       安装mysql和keepalived
VIP：166.111.69.10
    
要实现主主同步，可以先实现主从同步，即master1->master2的主从同步，然后master2->master1的主从同步.
这样，双方就完成了主主同步。
 
注意下面几点：
1）要保证同步服务期间之间的网络联通。即能相互ping通，能使用对方授权信息连接到对方数据库（防火墙开放3306端口）。
2）关闭selinux.
3）同步前，双方数据库中需要同步的数据要保持一致。这样，同步环境实现后，再次更新的数据就会如期同步了。
 

一、MySQL 主主同步环境部署

1、修改配置文件

　　Master 1 的有关复制的配置如下

[mysqld]
log-bin=mysql-bin
server-id=1
log_slave_updates=1

　　Master 2 的有关复制的配置如下

[mysqld]
log-bin=mysql-bin
server-id=2
log_slave_updates=1
read_only=1

2.创建复制用户

　　Master 1 中创建：

CREATE USER 'repl'@'192.168.49.128' IDENTIFIED BY '123';
GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.49.128';

　　Master 2 中创建：

CREATE USER 'repl'@'192.168.49.13' IDENTIFIED BY '123';
GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.49.13';

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：

(root@localhost) [(none)]> show master statusG
*************************** 1. row ***************************
File: mysql-bin.000009
Position: 2192
Binlog_Do_DB:
Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)

Master2上执行：

(root@localhost) [(none)]> show master statusG
*************************** 1. row ***************************
File: mysql-bin.000008
Position: 1574
Binlog_Do_DB: 
Binlog_Ignore_DB: 
Executed_Gtid_Set: 
1 row in set (0.00 sec)

Master 1 上 Change：

CHANGE MASTER TO
  MASTER_HOST='192.168.49.128',
  MASTER_USER='repl',
  MASTER_PASSWORD='123',
  MASTER_LOG_FILE='mysql-bin.000008',
  MASTER_LOG_POS=1574;

Master 2 上 Change：

CHANGE MASTER TO
  MASTER_HOST='192.168.49.13',
  MASTER_USER='repl',
  MASTER_PASSWORD='123',
  MASTER_LOG_FILE='mysql-bin.000009',
  MASTER_LOG_POS=2192;

4.分别在两个节点上执行start slave 语句，并通过show slave status G 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MySQL + Keepalived 故障转移的高可用环境

1）安装keepalived并将其配置成系统服务。

Master1和Master2两台机器上同样进行如下操作：

[root@master1 ~]# yum install -y openssl-devel

[root@master1 ~]# cd /usr/local/src/

[root@master1 src]# wget http://www.keepalived.org/software/keepalived-1.3.5.tar.gz

[root@master1 src]# tar -zvxf keepalived-1.3.5.tar.gz

[root@master1 src]# cd keepalived-1.3.5

[root@master1 keepalived-1.3.5]# ./configure --prefix=/usr/local/keepalived

[root@master1 keepalived-1.3.5]# make && make install

[root@master1 keepalived-1.3.5]# cp /usr/local/src/keepalived-1.3.5/keepalived/etc/init.d/keepalived /etc/rc.d/init.d/

[root@master1 keepalived-1.3.5]# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/

[root@master1 keepalived-1.3.5]# mkdir /etc/keepalived/

[root@master1 keepalived-1.3.5]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/

[root@master1 keepalived-1.3.5]# cp /usr/local/keepalived/sbin/keepalived /usr/sbin/

[root@master1 keepalived-1.3.5]# echo "/etc/init.d/keepalived start" >> /etc/rc.local

2）master1机器上的keepalived.conf配置。（下面配置中没有使用lvs的负载均衡功能，所以不需要配置虚拟服务器virtual server）

[root@master1 ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak

[root@master1 ~]# vim /etc/keepalived/keepalived.conf ＃清空默认内容，直接采用下面配置：

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 {
        166.111.69.100/24
    }
}

　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。

Master 2

[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 {
        166.111.49.100/24
    }
}

　　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 -p888888'
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。　

DB2上手动切换回DB1的脚本change_to_backup.sh：

#!/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

　Error：在测试过程中，可能遇到keepalived 启动失败的情况

上面这种情况是找不到PID 文件而报错,可手动指定PID文件的位置

查看keepalived.service

# vi /lib/systemd/system/keepalived.service

[Unit]
Description=LVS and VRRP High Availability Monitor
After=syslog.target network-online.target

[Service]
Type=forking
PIDFile=/usr/local/keepalived/var/run/keepalived.pid
KillMode=process
EnvironmentFile=-/usr/local/keepalived/etc/sysconfig/keepalived
ExecStart=/usr/local/keepalived/sbin/keepalived $KEEPALIVED_OPTIONS
ExecReload=/bin/kill -HUP $MAINPID

[Install]
WantedBy=multi-user.target

发现 PIDFile=/usr/local/keepalived/var/run/keepalived.pid 这个文件的路径并不存在

[root@centos02_stb keepalived]# find / -name keepalived.pid
/run/keepalived.pid

修改为 /run/keepalived.pid

运行命令

# systemctl daemon-reload #重新载入 systemd，扫描新的或有变动的单元

再运行就Ok了

service keepalived start
Starting keepalived (via systemctl): [ OK ]

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原文地址：https://www.cnblogs.com/Camiluo/p/10334735.html