About MySQL high availability: Keepalived dual master hot standby

Usually speaking of "dual-machine hot standby" means that both machines are running, but not both machines are providing services at the same time. When the one that provides services fails, the other one will automatically take over and provide services immediately, and the switching time is very short.

The working principle of Keepalived is VRRP (Virtual Router Redundancy Protocol) virtual routing redundancy protocol. There are two important concepts in VRRP: VRRP router and virtual router, master router and backup router.

VRRP router refers to the router running VRRP, which is a physical entity. Virtual router refers to the logical concept created by the VRRP protocol. A group of VRRP routers work together to form a virtual router. There is an election mechanism in Vrrp to select the route that provides services, that is, the master route, and the others become backup routes. When the master route fails, a master route will be re-elected from the backup route to continue working to ensure uninterrupted service.

Environment description:

OS: Ubuntu16.04
MASTER: 172.16.29.205
BACKUP: 172.16.29.197
VIP: 172.16.29.206

[root@masterr ~]# vi /etc/keepalived/keepalived.conf
global_defs {
notification_email {
test@sina.com
 }
notification_email_from  admin@test.com
smtp_server 127.0.0.1
smtp_connect_timeout 30
router_id MYSQL_HA      #标识，双主相同
 }
vrrp_instance VI_1 {
 state BACKUP           #两台都设置BACKUP
 interface eth0
 virtual_router_id 51       #主备相同
 priority 100           #优先级，backup设置90
 advert_int 1
 nopreempt             #不主动抢占资源，只在master这台优先级高的设置，backup不设置
 authentication {
 auth_type PASS
 auth_pass 1111
 }
 virtual_ipaddress {
 172.16.29.206
 }
}
virtual_server 172.16.29.206 3306 {
 delay_loop 2
 #lb_algo rr              #LVS算法，用不到，我们就关闭了
 #lb_kind DR              #LVS模式，如果不关闭，备用服务器不能通过VIP连接主MySQL
 persistence_timeout 50  #同一IP的连接60秒内被分配到同一台真实服务器
 protocol TCP
 real_server 172.16.29.205 3306 {   #检测本地mysql，backup也要写检测本地mysql
 weight 3
 notify_down /etc/keepalived/mysql.sh    #当mysq服down时，执行此脚本，杀死keepalived实现切换
 TCP_CHECK {
 connect_timeout 3    #连接超时
 nb_get_retry 3       #重试次数
 delay_before_retry 3 #重试间隔时间
  }
}   
[root@masterr ~]# vi /usr/local/keepalived/mysql.sh
#!/bin/bash
sudo service keepalived stop
[root@masterr ~]# chmod +x /usr/local/keepalived/mysql.sh
[root@masterr ~]# /etc/init.d/keepalived start

backup server only changes the priority to 90, nopreempt is not set, and real_server sets the local IP.

3. Test high availability

1. Connect through VIP through Mysql client to see if the connection is successful.

2. Stop the master mysql service and check whether it can be switched to it normally. You can use the ip addr command to check which server the VIP is on.

3. You can see the master/backup switching process by checking the /var/log/messges log.

4. After the master server recovers from failure, whether it actively seizes resources and becomes an active server.

This article explains the use of Keepalived to achieve high availability for MySQL. For more related recommendations, please pay attention to the php Chinese website.

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