# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:33:80:d5 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.20/24 brd 192.168.1.255 scope global noprefixroute eth0
valid_lft forever preferred_lft forever
inet 192.168.1.30/32 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::4b20:2e16:a957:f9a1/64 scope link noprefixroute
valid_lft forever preferred_lft forever
---------------------
查看/var/log/messages日志，可以看到主备切换过程：
Apr 8 15:27:16 hosts systemd: Stopping MySQL Server...
Apr 8 15:27:16 hosts Keepalived_healthcheckers[11048]: TCP connection to [192.168.1.10]:3306 failed.
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: TCP connection to [192.168.1.10]:3306 failed.
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Check on service [192.168.1.10]:3306 failed after 1 retry.
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Removing service [192.168.1.10]:3306 from VS [192.168.1.30]:3306
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: IPVS (cmd 1160, errno 2): No such destination
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Executing [/tmp/mysql.sh] for service [192.168.1.10]:3306 in VS [192.168.1.30]:3306
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Lost quorum 1-0=1 > 0 for VS [192.168.1.30]:3306
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Remote SMTP server [127.0.0.1]:25 connected.
Apr 8 15:27:19 hosts Keepalived_vrrp[11049]: VRRP_Instance(VI_1) sent 0 priority
Apr 8 15:27:19 hosts Keepalived_vrrp[11049]: VRRP_Instance(VI_1) removing protocol VIPs.
Apr 8 15:27:19 hosts Keepalived[11047]: Stopping
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: IPVS (cmd 1156, errno 2): No such file or directory
Apr 8 15:27:19 hosts Keepalived_healthcheckers[11048]: Stopped
Apr 8 15:27:20 hosts Keepalived_vrrp[11049]: Stopped
Apr 8 15:27:20 hosts Keepalived[11047]: Stopped Keepalived v1.3.5 (03/19,2017), git commit v1.3.5-6-g6fa32f2
Apr 8 15:27:27 hosts systemd: Stopped MySQL Server.
---------------------
恢复master服务器故障，看是否主动抢占资源，成为活动服务器。
master上启动mysql服务和keepalived服务：
# systemctl start mysqld
# systemctl start keepalived
# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:0c:29:cf:ab:c4 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.10/24 brd 192.168.1.255 scope global noprefixroute eth0
valid_lft forever preferred_lft forever
inet6 fe80::fe8e:3c2f:4d32:e9fd/64 scope link noprefixroute
valid_lft forever preferred_lft forever
---------------------
可以看到，即使master故障恢复，也没有抢占资源，VIP仍然在backup上，这是因为之前已经配置了master为非抢占模式（nopreempt）。
不过需要注意的是：
nopreempt这个参数只能用于state为BACKUP的情况，所以在配置的时候要把master和backup的state都设置成BACKUP，这样才会实现keepalived的非抢占模式！
也就是说：
* 当state状态一个为MASTER，一个为BACKUP的时候，加不加nopreempt这个参数都是一样的效果。即都是根据priority优先级来决定谁抢占vip资源的，是抢占模式！
* 当state状态都设置成BACKUP，如果不配置nopreempt参数，那么也是看priority优先级决定谁抢占vip资源，即也是抢占模式。