mysql主备模式 mysql keepalived主备切换

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mob64ca1414098d 2023-08-12 20:14:49

文章标签 mysql主备模式 mysql SSL 数据 文章分类 MySQL 数据库

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。

环境概述：
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，通过浮动IP实现Mysql双主对外连接的统一接口。即客户端通过浮动IP连接数据库；当其中一台宕机后，浮动IP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。

mysql主备模式 mysql keepalived主备切换_mysql

环境描述：
操作系统：Centos6.5
Mysql版本：5.5.53
Master1：192.168.1.4 安装mysql和keepalived
Master2：192.168.1.5 安装mysql和keepalived
浮动IP：192.168.1.10

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。
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。

一、Mysql主主同步环境部署

---------------master1服务器操作记录---------------

在my.cnf文件的[mysqld]配置区域添加下面内容：

[root@master1 ~]# vim /etc/my.cnf 
[mysqld]
port = 3306
socket = /tmp/mysql.sock
log_slave_updates
log-bin = mysql-bin
server-id = 1
binlog-ignore-db=mysql
#auto_increment_increment = 2
##auto_increment_offset = 2

[root@master1 ~]# /etc/init.d/mysqld restart
Shutting down MySQL. SUCCESS!
Starting MySQL.. SUCCESS!

数据同步授权,授权yhf用户:
mysql> grant replication slave on . to yhf@'%' identified by '123456';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges; 
Query OK, 0 rows affected (0.00 sec)

最好将库锁住，仅仅允许读，以保证数据一致性；待主主同步环境部署后再解锁；
锁住后，就不能往表里写数据，但是重启mysql服务后就会自动解锁！

mysql> flush tables with read lock; //注意该参数设置后，如果自己同步对方数据，同步前一定要记得先解锁！
Query OK, 0 rows affected (0.00 sec)

查看下log bin日志和pos值位置

mysql> show master status;
+------------------+----------+--------------+--------------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+--------------------------+-------------------+
| mysql-bin.000004 | 430 | | mysql,information_schema | |
+------------------+----------+--------------+--------------------------+-------------------+
1 row in set (0.00 sec)

---------------master2服务器操作记录---------------
在my.cnf文件的[mysqld]配置区域添加下面内容：

[root@master2 ~]# vim /etc/my.cnf 
[mysqld]
port = 3306
socket = /home/mysql/tmp/mysql.sock
log_slave_updates
log-bin = mysql-bin
server-id = 2
binlog-ignore-db=mysql
#auto_increment_increment = 2
##auto_increment_offset = 1

[root@master2 ~]# /etc/init.d/mysqld restart
Shutting down MySQL.. SUCCESS!
Starting MySQL.. SUCCESS!

数据同步授权,授权yhf用户:
mysql> grant replication slave on . to yhf@'%' identified by '123456';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges; 
Query OK, 0 rows affected (0.00 sec)

mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)

mysql> show master status;
+------------------+----------+--------------+--------------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+--------------------------+-------------------+
| mysql-bin.000003 | 430 | | mysql,information_schema | |
+------------------+----------+--------------+--------------------------+-------------------+
1 row in set (0.00 sec)

---------------master1服务器做同步操作---------------

mysql> unlock tables; //先解锁，将对方数据同步到自己的数据库中
mysql> slave stop；

mysql> change master to master_host='192.168.1.5',master_user='hyf', master_password='123456',master_log_file='mysql-bin.000003 ',master_log_pos=430;
Query OK, 0 rows affected (0.03 sec)

mysql> slave start;
Query OK, 0 rows affected (0.00 sec)

mysql> show slave status\G
1. row 
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.5
Master_User: hyf
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000003
Read_Master_Log_Pos: 168522635
Relay_Log_File: master-relay-bin.000036
Relay_Log_Pos: 430
Relay_Master_Log_File: mysql-bin.000003
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB: 
Replicate_Ignore_DB: 
Replicate_Do_Table: 
Replicate_Ignore_Table: 
Replicate_Wild_Do_Table: 
Replicate_Wild_Ignore_Table: 
Last_Errno: 0
Last_Error: 
Skip_Counter: 0
Exec_Master_Log_Pos: 168522635
Relay_Log_Space: 168550131
Until_Condition: None
Until_Log_File: 
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File: 
Master_SSL_CA_Path: 
Master_SSL_Cert: 
Master_SSL_Cipher: 
Master_SSL_Key: 
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error: 
Last_SQL_Errno: 0
Last_SQL_Error: 
Replicate_Ignore_Server_Ids: 
Master_Server_Id: 1
1 row in set (0.00 sec)

这样，master1就和master2实现了主从同步，即master1同步master2的数据。

---------------master2服务器做同步操作---------------

mysql> unlock tables; //先解锁，将对方数据同步到自己的数据库中
mysql> slave stop；
mysql> change master to master_host='192.168.1.4',master_user='hyf', master_password='123456',master_log_file='mysql-bin.000004 ',master_log_pos=430;
Query OK, 0 rows affected (0.03 sec)

mysql> slave start;
Query OK, 0 rows affected (0.00 sec)

mysql> show slave status\G
1. row 
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.4
Master_User: hyf
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000004
Read_Master_Log_Pos: 165416799
Relay_Log_File: master1-relay-bin.000034
Relay_Log_Pos: 459
Relay_Master_Log_File: mysql-bin.000004
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB: 
Replicate_Ignore_DB: 
Replicate_Do_Table: 
Replicate_Ignore_Table: 
Replicate_Wild_Do_Table: 
Replicate_Wild_Ignore_Table: 
Last_Errno: 0
Last_Error: 
Skip_Counter: 0
Exec_Master_Log_Pos: 165416799
Relay_Log_Space: 614
Until_Condition: None
Until_Log_File: 
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File: 
Master_SSL_CA_Path: 
Master_SSL_Cert: 
Master_SSL_Cipher: 
Master_SSL_Key: 
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error: 
Last_SQL_Errno: 0
Last_SQL_Error: 
Replicate_Ignore_Server_Ids: 
Master_Server_Id: 2
1 row in set (0.00 sec)

这样，master2就和master1实现了主从同步，即master2也同步master1的数据。

以上表明双方已经实现了mysql主主同步。
当运行一段时间后，要是发现同步有问题，比如只能单向同步，双向同步失效。可以重新执行下上面的change master同步操作，只不过这样同步后，只能同步在此之后的更新数据。下面开始进行数据验证：

-----------------主主同步效果验证---------------------

mysql> create database zsz;
mysql> use zsz;

mysql> create table tb4(id smallint unsigned auto_increment primary key,username varchar(20) not null); 
Query OK, 0 rows affected (0.01 sec)

mysql> select * from tb4;
Empty set (0.00 sec)

mysql> insert tb4 (id,username) values (4,'jona'); 
Query OK, 1 row affected (0.00 sec)

mysql> select id,username from tb4;
+----+----------+
| id | username |
+----+----------+
| 4 | jona |
+----+----------+
1 row in set (0.00 sec)

然后在master2数据库上查看，发现数据已经同步过来了!

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
| zsz |
+--------------------+
5 rows in set (0.00 sec)

mysql> use zsz;
Database changed
mysql> show tables;
+---------------+
| Tables_in_zsz |
+---------------+
| tb4 |
+---------------+
1 rows in set (0.00 sec)
mysql> select id,username from tb4;
+----+----------+
| id | username |
+----+----------+
| 4 | jona |
+----+----------+
1 row in set (0.00 sec)

2）在master2数据库上写入新数据

mysql> insert tb4 (id,username) values (1,'jona'); 
Query OK, 1 row affected (0.01 sec)

mysql> select id,username from tb4;
+----+----------+
| id | username |
+----+----------+
| 1 | jona |
| 4 | jona |
+----+----------+
2 rows in set (0.00 sec)

然后在master1数据库上查看，发现数据也已经同步过来了!

mysql> select id,username from tb4;
+----+----------+
| id | username |
+----+----------+
| 1 | jona |
| 4 | jona |
+----+----------+
2 rows in set (0.00 sec)

至此，Mysql主主同步环境已经实现。

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：
! Configuration File for keepalived

global_defs {
notification_email {br/>root@localhost
}
notification_email_from root@localhost
smtp_server localhost
smtp_connect_timeout 30
router_id LVS_redis
}

vrrp_script chk_mysql_port { #检测mysql服务是否在运行。有很多方式，比如进程，用脚本检测等等
script "/etc/keepalived/scripts/chk_mysql.sh" #这里通过脚本监测
interval 1 #脚本执行间隔，每2s检测一次
weight -5 #脚本结果导致的优先级变更，检测失败（脚本返回非0）则优先级 -5
fall 2 #检测连续2次失败才算确定是真失败。会用weight减少优先级（1-255之间）
rise 1 #检测1次成功就算成功。但不修改优先级
}

vrrp_instance VI_1 { 
state MASTER 
interface eth0 #指定虚拟ip的网卡接口
mcast_src_ip 192.168.1.4
virtual_router_id 51 #路由器标识，MASTER和BACKUP必须是一致的
priority 101 #定义优先级，数字越大，优先级越高，在同一个vrrp_instance下，MASTER的优先级必须大于BACKUP的优先级。这样MASTER故障恢复后，就可以将VIP资源再次抢回来 
advert_int 1 
authentication { 
auth_type PASS 
auth_pass 1111 
}
virtual_ipaddress { 
192.168.1.10
}

track_script { 
chk_mysql_port 
}
}

编写切换脚本。KeepAlived做心跳检测，如果Master的MySQL服务挂了(3306端口挂了),那么它就会选择自杀。Slave的KeepAlived通过心跳检测发现这个情况，就会将浮动ip的请求接管

[root@master1 ~]# vim /etc/keepalived/scripts/chk_mysql.sh 
#!/bin/bash
counter=$(netstat -na|grep "LISTEN"|grep "3306"|wc -l)
if [ "${counter}" -eq 0 ]; then
/etc/init.d/keepalived stop
fi

[root@master1 ~]# chmod 755 /etc/keepalived/scripts/chk_mysql.sh

启动keepalived服务
[root@master1 ~]# /etc/init.d/keepalived start
正在启动 keepalived： [确定]

4）master2机器上的keepalived配置。master2机器上的keepalived.conf文件只修改priority为90、nopreempt不设置、real_server设置本地IP。

[root@master2 ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
[root@master2 ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalived

global_defs {
notification_email {br/>root@localhost
}
notification_email_from root@localhost
smtp_server localhost
smtp_connect_timeout 30
router_id LVS_redis
}

vrrp_script chk_mysql_port {
script "/etc/keepalived/scripts/chk_mysql.sh"
interval 1
weight -5
fall 2
rise 1
}

vrrp_instance VI_1 {
state BACKUP
interface eth0
mcast_src_ip 192.168.1.5
virtual_router_id 51
priority 99
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.1.10
}

track_script {
chk_mysql_port
}
}

[root@master2 ~]# cat /etc/keepalived/scripts/chk_mysql.sh 
#!/bin/bash
counter=$(netstat -na|grep "LISTEN"|grep "3306"|wc -l)
if [ "${counter}" -eq 0 ]; then
/etc/init.d/keepalived stop
fi

[root@master2 ~]# chmod 755 /etc/keepalived/scripts/chk_mysql.sh

启动keepalived服务
[root@master2 ~]# /etc/init.d/keepalived start
正在启动 keepalived： [确定]

5）master1和master2两台服务器都要授权允许root用户远程登录，用于在客户端登陆测试！

mysql> grant all on . to root@'%' identified by "1234567";
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

三、Mysql＋keepalived故障转移的高可用测试
1）通过Mysql客户端通过浮动ip连接，看是否连接成功。
比如，在远程一台测试机上连接，通过浮动IP可以正常连接（下面的连接权限要是在服务端提前授权的）

[root@dev-new-test ~]# mysql -h192.168.1.10 -uroot -p123456
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 9578
Server version: 5.5.53-log Source distribution

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use zsz;
Database changed
mysql> select id,username from tb4;
+----+----------+
| id | username |
+----+----------+
| 1 | jona |
| 4 | jona |
+----+----------+
2 rows in set (0.00 sec)

mysql>

2）默认情况下，浮动ip是在master1上的。使用"ip addr"命令查看vip切换情况

[root@master1 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65326 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
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 qlen 1000
link/ether 12:54:00:31:22:4q brd ff:ff:ff:ff:ff:ff
inet 192.168.1.4/24 brd 192.168.1.255 scope global eth0
inet 192.168.1.10/32 scope global eth0 //这个32位子网掩码的浮动ip地址表示该资源目前还在master1机器上
inet6 fe80::3224:ff:f33c:2532/64 scope link
valid_lft forever preferred_lft forever

停止master1机器上的mysql服务，根据配置中的脚本，mysql服务停了，keepalived也会停，从而vip资源将会切换到master2机器上。（mysql服务没有起来的时候，keepalived服务也无法顺利启动！）

[root@master1 ~]# /etc/init.d/mysqld stop
Shutting down MySQL.. SUCCESS!
[root@master1 ~]# ps -ef|grep mysql
root 25812 21588 0 17:30 pts/0 00:00:00 grep mysql
[root@master1 ~]# ps -ef|grep keepalived
root 25814 21588 0 17:30 pts/0 00:00:00 grep keepalived
[root@master1 ~]# ip addr 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
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 qlen 1000
link/ether 12:54:30:12:25:4q brd ff:ff:ff:ff:ff:ff
inet 192.168.1.4/24 brd 192.168.1.255 scope global eth0
inet6 fe80::2344:ff:fe5c:3542/64 scope link
valid_lft forever preferred_lft forever

如上结果，发现32位子网掩码的vip没有了，说明此时浮动IP已不在master1机器上了

查看下master1的系统日志，如下，会发现vip资源已经切换走了

[root@master1 ~]# tail -f /var/log/messages

再到master2机器上，发现vip资源的确切换过来了
[root@master2 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
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 qlen 1000
link/ether 12:54:00:31:22:4q brd ff:ff:ff:ff:ff:ff
inet 192.168.1.5/24 brd 192.168.1.255 scope global eth0
inet 192.168.1.10/32 scope global eth0 
inet6 fe80::3224:ff:f33c:2532/64 scope link
valid_lft forever preferred_lft forever

查看master2的系统日志

[root@master2 ~]# tail -f /var/log/messages

3）再次启动master1的mysql和keepalived服务。（注意：如果restart重启mysql，那么还要启动下keepalived，因为mysql重启，根据脚本会造成keepalived关闭）
注意：一定要先启动mysql服务，然后再启动keepalived服务。如果先启动keepalived服务，按照上面的配置，mysql没有起来，就会自动关闭keepalived。

[root@master1 ~]# /etc/init.d/mysqld start
Starting MySQL.. SUCCESS!

[root@master1 ~]# /etc/init.d/keepalived start
正在启动 keepalived： [确定]

启动这两个服务器后，稍微等过一会儿，注意观察会发现vip资源再次从master2机器上切换回来了。

[root@master1 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
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 qlen 1000
link/ether 12:54:00:31:22:4q brd ff:ff:ff:ff:ff:ff
inet 192.168.1.4/24 brd 192.168.1.255 scope global eth0
inet 192.168.1.10/32 scope global eth0 
inet6 fe80::3224:ff:f33c:2532/64 scope link
valid_lft forever preferred_lft forever

再看看master2机器，发现vip资源又被恢复后的master1抢过去了

[root@master2 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
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 qlen 1000
link/ether 12:54:00:31:22:4q brd ff:ff:ff:ff:ff:ff
inet 192.168.1.5/24 brd 192.168.1.255 scope global eth0
inet6 fe80::3224:ff:f33c:2532/64 scope link
valid_lft forever preferred_lft forever

4）同样，关闭master1机器的keepalived服务，vip资源会自动切换到master2机器上。当master1的keepalived服务恢复后，会将vip资源再次切回来。
以上在vip资源切换过程中，对于客户端连接mysql（使用vip连接）来说几乎是没有任何影响的。

------------------------------------温馨提示（Keepalived的抢占和非抢占模式）---------------------------------------
keepalive是基于vrrp协议在linux主机上以守护进程方式，根据配置文件实现健康检查。
VRRP是一种选择协议，它可以把一个虚拟路由器的责任动态分配到局域网上的VRRP路由器中的一台。
控制虚拟路由器IP地址的VRRP路由器称为主路由器，它负责转发数据包到这些虚拟IP地址。
一旦主路由器不可用，这种选择过程就提供了动态的故障转移机制，这就允许虚拟路由器的IP地址可以作为终端主机的默认第一跳路由器。

keepalive通过组播，单播等方式（自定义），实现keepalive主备推选。工作模式分为抢占和非抢占（通过参数nopreempt来控制）。
1）抢占模式：
主服务正常工作时，虚拟IP会在主上，备不提供服务，当主服务优先级低于备的时候，备会自动抢占虚拟IP，这时，主不提供服务，备提供服务。
也就是说，工作在抢占模式下，不分主备，只管优先级。

如上配置，不管keepalived.conf里的state配置成master还是backup，只看谁的priority优先级高（一般而言，state为MASTER的优先级要高于BACKUP）。
priority优先级高的那一个在故障恢复后，会自动将VIP资源再次抢占回来！！

2）非抢占模式：
这种方式通过参数nopreempt（一般设置在advert_int的那一行下面）来控制。不管priority优先级，只要MASTER机器发生故障，VIP资源就会被切换到BACKUP上。
并且当MASTER机器恢复后，也不会去将VIP资源抢占回来，直至BACKUP机器发生故障时，才能自动切换回来。

千万注意：
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：
a）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！
b）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。
c）当state状态都设置成backup，如果配置nopreempt参数，那么就不会去考虑priority优先级了，是非抢占模式！即只有vip当前所在机器发生故障，另一台机器才能接管vip。即使优先级高的那一台机器恢复后也不会主动抢回vip，只能等到对方发生故障，才会将vip切回来。

---------------------------------mysql状态检测脚本优化---------------------------------
上面的mysql监测脚本有点过于简单且粗暴，即脚本一旦监测到Master的mysql服务关闭，就立刻把keepalived服务关闭，从而实现vip转移！

下面对该脚本进行优化，优化后，当监测到Master的mysql服务关闭后，就会将vip切换到Backup上（但此时Master的keepalived服务不会被暴力kill）
当Master的mysql服务恢复后，就会再次将VIP资源切回来！

[root@master ~]# cat /etc/keepalived/scripts/chk_mysql.sh
#!/bin/bash
MYSQL=/usr/local/mysql/bin/mysql
MYSQL_HOST=localhost
MYSQL_USER=root
MYSQL_PASSWORD=123456
CHECK_TIME=3

#mysql is working MYSQL_OK is 1 , mysql down MYSQL_OK is 0

MYSQL_OK=1

function check_mysql_helth (){
$MYSQL -h $MYSQL_HOST -u $MYSQL_USER -p${MYSQL_PASSWORD} -e "show status;" >/dev/null 2>&1
if [ $? = 0 ] ;then
MYSQL_OK=1
else
MYSQL_OK=0
fi
return $MYSQL_OK
}
while [ $CHECK_TIME -ne 0 ]
do
let "CHECK_TIME -= 1"
check_mysql_helth
if [ $MYSQL_OK = 1 ] ; then
CHECK_TIME=0
exit 0
fi
if [ $MYSQL_OK -eq 0 ] && [ $CHECK_TIME -eq 0 ]
then
#pkill keepalived
exit 1

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