1、准备
操作系统版本：CentOS6.5 64位
MySQL版本：5.6.21
Keepalived版本：v1.2.23 1.2.24
节点A：192.168.43.134
节点B：192.168.43.135
VIP（虚拟IP）：192.168.43.130
下文中说到
VIP即指192.168.43.130
节点A或134即指192.168.43.134
节点B或135即指192.168.43.135
MySQL高可用主要是通过Keepalived这款软件来实现多个节点的服务可用性检测和故障转移，对外提供VIP地址供客户端连接，由keepalived根据服务的状态，负责将vip漂移到真实可用的机器上，从而实现服务的高可用。阅读本文前，需要先安装MySQL、Keepalived以及MySQL主主同步配置，可参考我之前写的文章自行安装与配置：
Linux下安装Lnmp环境之准备篇（一）
Linux下安装Lnmp环境之Mysql（二）
MySQL主主互备配置过程详解
Linux下keepalived安装与配置
本文配置keepalived为非抢占模式
节点A配置
vi /etc/keepalived/keepalived.conf
! Configuration File for keepalived
global_defs {
### 标识本节点的字条串,通常为 功能+IP
router_id db_134
}
vrrp_instance VI_1 {
#两个节点都为BACKUP状态，根据优先级大小判断谁为MASTER
state BACKUP
interface eth0
#虚拟路由的ID号，每个节点设置必须一样
virtual_router_id 51
#节点优先级 MASTER高于BACKUP
priority 100
advert_int 1
nopreempt #非抢占模式
authentication {
auth_type PASS
auth_pass 1111
}
# 虚拟IP池
virtual_ipaddress {
192.168.43.130
}
}
virtual_server 192.168.43.130 3306{
#健康检查时间间隔，单位：秒
delay_loop 2
lb_algo wrr
lb_kind DR
persistence_timeout 50
protocol TCP
real_server 192.168.43.134 3306 {
weight 3
notify_down /etc/keepalived/mysql.sh # 当mysql服务down了之后，执行的脚本
TCP_CHECK {
connect_timeout 10 # mysql连接超时时长（秒）
nb_get_retry 3 # mysql服务连接失败，重试次数
delay_before_retry 3 #每隔3秒检测一次mysql服务是否可用
connect_port 3306
}
}
}/etc/keepalived/mysql.sh配置：
#!/bin/sh
pkill keepalived当mysql服务停止时，会执行/etc/keepalived/mysql.sh脚本，将当前节点的keepalived服务停止，这样vip就会切换到另外一个节点上，从而实现了服务的高可用。
节点B配置
vi /etc/keepalived/keepalived.conf
! Configuration File for keepalived
global_defs {
router_id db_135
}
vrrp_instance VI_1 {
#两个节点都为BACKUP状态，根据优先级大小判断谁为MASTER
state BACKUP
interface eth0
virtual_router_id 51
#注意：比MASTER小
priority 90
advert_int 1
nopreempt #非抢占模式
authentication {
auth_type PASS
auth_pass 1111
}
#虚拟IP池
virtual_ipaddress {
192.168.43.130
}
}
virtual_server 192.168.43.130 3306 {
delay_loop 2
lb_algo wrr
lb_kind DR
persistence_timeout 50
protocol TCP
real_server 192.168.43.135 3306 {
weight 3
notify_down /etc/keepalived/mysql.sh # 当mysql服务down了之后，执行
的脚本
TCP_CHECK {
connect_timeout 10 # mysql连接超时时长（秒）
nb_get_retry 3 # mysql服务连接失败，重试次数
delay_before_retry 3 #每隔3秒检测一次mysql服务是否可用
connect_port 3306
}
}
}/etc/keepalived/mysql.sh配置同节点A
#!/bin/sh
pkill keepalived启动MySQL和Keepalived服务
service mysqld start
service keepalived start注意：先启动mysql，再启动keepalived。因为keepalived启动之后会去连接mysql，检测服务是否可用，如果3次都没连接成功，则会将keepalived进程杀死。
连接测试
注意：连接到VIP地址，而非直接连接到真实的MySQL服务器。
先看看vip漂在哪台服务器上：
ip add
从上图得知，此时VIP漂移在节点1（192.168.43.134）上。
注：两个节点 在指定ip连接到mysql时，需要授权配置远程连接的帐号、密码和ip。如：
grant all privileges on *.* to 'root'@'%' identified by 'password' with grant option;从虚拟IP 192.168.43.130 登录Mysql
mysql -u root -proot -h 192.168.43.130
故障转移测试
从上面连接测试得知，此时vip漂移在192.168.43.134节点上，所以通过vip（192.168.43.130）连接到的真实服务器是192.168.43.134。将134的mysql服务停止，观察vip是否会切换到135上。
#通过/var/log/message文件可以看到keepalived故障的日志
tail -f /var/log/message节点A的日志：
Sep 25 16:00:32 edu-mysql-01 Keepalived_healthcheckers[3517]: TCP connection to [192.168.43.134]:3306 failed.
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: TCP connection to [192.168.43.134]:3306 failed.
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: Check on service [192.168.43.134]:3306 failed after 1 retry.
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: Removing service [192.168.43.134]:3306 from VS [192.168.43.130]:3306
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: Executing [/etc/keepalived/mysql.sh] for service [192.168.43.134]:3306 in VS [192.168.43.130]:3306
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: Lost quorum 1-0=1 > 0 for VS [192.168.43.130]:3306
Sep 25 16:00:35 edu-mysql-01 kernel: IPVS: __ip_vs_del_service: enter
Sep 25 16:00:35 edu-mysql-01 Keepalived[3515]: Stopping
Sep 25 16:00:35 edu-mysql-01 Keepalived_healthcheckers[3517]: Stopped
Sep 25 16:00:35 edu-mysql-01 Keepalived_vrrp[3518]: VRRP_Instance(VI_1) sent 0 priority
Sep 25 16:00:35 edu-mysql-01 Keepalived_vrrp[3518]: VRRP_Instance(VI_1) removing protocol VIPs.
Sep 25 16:00:36 edu-mysql-01 Keepalived_vrrp[3518]: Stopped
Sep 25 16:00:36 edu-mysql-01 Keepalived[3515]: Stopped Keepalived v1.2.23 (09/12,2016)前三行是keepalived心跳检测，每秒检测一次mysql服务是否可用，当第3次连接失败时，将该服务从lvs真实服务器列表中移除（第4行），并执行/etc/keepalived/mysql.sh脚本（第5行）停止keepalived服务，转让vip使用权。
节点B的日志：
Sep 25 16:00:36 edu-mysql-02 Keepalived_vrrp[3457]: VRRP_Instance(VI_1) Transition to MASTER STATE
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: VRRP_Instance(VI_1) Entering MASTER STATE
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: VRRP_Instance(VI_1) setting protocol VIPs.
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: VRRP_Instance(VI_1) Sending/queueing gratuitous ARPs on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:37 edu-mysql-02 Keepalived_healthcheckers[3456]: Netlink reflector reports IP 192.168.43.130 added
Sep 25 16:00:42 edu-mysql-02 Keepalived_vrrp[3457]: Sending gratuitous ARP on enp0s3 for 192.168.43.130
Sep 25 16:00:42 edu-mysql-02 Keepalived_vrrp[3457]: VRRP_Instance(VI_1) Sending/queueing gratuitous ARPs on enp0s3 for 192.168.43.130节点2当前是BACKUP状态，当收到节点1挂掉的通知后，将自己的状态转换为master状态（第1行），接着将vip（192.168.43.130）绑定到enp0s3网卡上（第3到第5行）。
查看故障转移后的vip
从上图可知，vip成功从134转移到了135上。
此时在之前已经和vip建立了连接的mysql客户端当中，再执行sql时，第一次会执行失败，因为之前的连接已经断开，第二次执行时，会尝试重新连接到vip对应的新的mysql真实服务器上。
