前言:(PS: 前言是后来修改本文时加的)对于这篇文章,有博友提出了一些疑问和见解, 有了博友的关注,也促使我想把这套东西做的更实用、更安全。后来又经过思考, 对脚本中一些条件和行为做了些改变。经过几次修改,现在终于敢说让小伙伴本使用这套东西了。
主要目的:
以双主结构配合keepalived解决MySQL主从结构中主库的单点故障;同时通过具体的查询语句提供更细粒度、更为真实的关于主库可用性的判断。
基本思路:
将DB1和DB2做成主动被动模式的双主结构:DB1主动、DB2被动,通过keepalived的VIP对外,将VIP设置成原DB1的IP,保证改造过程对代码透明
三个前提:
两台MySQL的配置文件里需要加上“log_slave_updates = 1”;
并且“备用机”通过“read_only”参数实现除root用户之外的只读特性;
分别在两个数据库创建test.test表,插入几条数据,供检测脚本使用。
正常时,VIP在DB1,通过keepalived调用脚本定期检查mysql服务可用性(通过一个低权限用户连接mysql服务器并执行一个简单查询,根据返回结果来判定mysql是否可用)
若无法执行查询:
1. 第一次检测失败后,检查服务状态,:
2. 开始执行系列切换动作
3. 管理员修复DB1后,通过脚本“change_to_backup.sh”将主库切换回DB1。脚本思路如下: 注:涉及到切换主备,就会有中断时间,所以推荐此步骤在业务低谷期执行
关于“数据一致性”和“切换时间”: 连续两次失败以后,通过对主MySQL设置read_only属性,同时kill掉用户线程来保证在DB2接管服务之前,DB1上已经没有写操作,避免主从数据不一致。并且切换时间基本上是可确定的: 30s(两次检测间隔)+2s(等待kill命令时间)+约1s(keepalived 切换VIP),总时间不会超过35s。 |
以上是大致思路,具体实现看过下面的脚本,就会一目了然了。
DB1上keepalived 配置
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! Configuration File
for
keepalived
vrrp_script chk_mysql {
script
"/etc/keepalived/check_mysql.sh"
interval 30
#这里我的检查间隔设置的比较长,因为我们数据库前面有redis做缓存,数据库一两分钟级别的中断对整体可用性影响不大。这也是我没有采用成熟的方案而自己搞了这一套方案的“定心丸”
}
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 em2
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 {
192.168.1.5
/24
}
}
|
/etc/keepalived/check_mysql.sh脚本内容如下(主要的判断逻辑都在这里)
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#!/bin/sh
###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
"/bin/sh*"
|
grep
"?"
|
grep
"?"
|
grep
-
v
"grep"
|
wc
-l` -gt 2 ];
then
#理论上这里应该是1,但是实验的结果却是2
exit
0
fi
alias
mysql_con=
'mysql -uxxxx -pxxxx'
###定义一个简单判断mysql是否可用的函数
function
excute_query {
mysql_con -e
"select * from test.test;"
2>>
/etc/keepalived/logs/check_mysql
.err
}
###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-----"
>>
/etc/keepalived/logs/check_mysql
.err
/sbin/service
keepalived stop &>>
/etc/keepalived/logs/check_mysql
.err
echo
-e
"\n@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n"
>>
/etc/keepalived/logs/check_mysql
.err
}
###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-----"
>>
/etc/keepalived/logs/check_mysql
.err
sleep
30
excute_query
if
[ $? -
ne
0 ];
then
echo
-e
"`date "
+%F %H:%M:%S
"` -----still can't execute query-----"
>>
/etc/keepalived/logs/check_mysql
.err
###对DB1设置read_only属性
echo
-e
"`date "
+%F %H:%M:%S
"` -----set read_only = 1 on DB1-----"
>>
/etc/keepalived/logs/check_mysql
.err
mysql_con -e
"set global read_only = 1;"
2>>
/etc/keepalived/logs/check_mysql
.err
###kill掉当前客户端连接
echo
-e
"`date "
+%F %H:%M:%S
"` -----kill current client thread-----"
>>
/etc/keepalived/logs/check_mysql
.err
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-----"
>>
/etc/keepalived/logs/check_mysql
.err
/sbin/service
keepalived stop &>>
/etc/keepalived/logs/check_mysql
.err
echo
-e
"\n@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n"
>>
/etc/keepalived/logs/check_mysql
.err
else
echo
-e
"`date "
+%F %H:%M:%S
"` -----query ok after 30s-----"
>>
/etc/keepalived/logs/check_mysql
.err
echo
-e
"\n@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n"
>>
/etc/keepalived/logs/check_mysql
.err
fi
}
###检查开始: 执行查询
excute_query
if
[ $? -
ne
0 ];
then
/sbin/service
mysql status &>
/dev/null
if
[ $? -
ne
0 ];
then
service_error
else
query_error
fi
fi
|
DB2上keepalived配置:
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! Configuration File
for
keepalived
vrrp_instance VI_1 {
state BACKUP
interface em2
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 {
192.168.1.5
/24
}
}
|
/etc/keepalived/notify_master_mysql.sh脚本内容:
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#!/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
alias
mysql_con=
'mysql -uroot -pxxxx -e "show slave status\G;" 2>/dev/null'
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|
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|
egrep
-w
"Master_Log_File|Read_Master_Log_Pos|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}'
`
Exec_Master_Log_Pos=`
echo
$log_file_pos|
awk
'{print $6}'
`
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"
|
/bin/mailx
-s
"DB2 keepalived change to MASTER"
\
lijiankai@dm.com 2>> $change_log
echo
-e
"@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n"
>> $change_log
}
slave_info slave_status
if
[ $Slave_IO_Running = Yes -a $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
[ $Read_Master_Log_Pos = $Exec_Master_Log_Pos ]
do
if
[ $i -lt 10 ];
then
#将等待exec_pos追上read_pos的时间限制为10s
echo
-e
"`date "
+%F %H:%M:%S"` -----Master_Log_File=$Master_Log_File. Exec_Master_Log_Pos($Exec_Master_Log_Pos) is behind Read_Master_Lo
g_Pos($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=$Read_Master_Log_Pos Exec_Ma
ster_Log_Pos=$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=$Read_Master_Log_Pos Exec_Master_Log_Po
s=$Exec_Master_Log_Pos" >> $change_log
action
fi
|
DB2上手动切换回DB1的脚本change_to_backup.sh:
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#!/bin/sh
###手动执行将主库切换回DB1的操作
alias
mysql_con=
'mysql -uxxxx -pxxxx'
echo
-e
"`date "
+%F %H:%M:%S
"` -----change to BACKUP manually-----"
>>
/etc/keepalived/logs/state_change
.log
echo
-e
"`date "
+%F %H:%M:%S
"` -----set read_only = 1 on DB2-----"
>>
/etc/keepalived/logs/state_change
.log
mysql_con -e
"set global read_only = 1;"
2>>
/etc/keepalived/logs/state_change
.log
###kill掉当前客户端连接
echo
-e
"`date "
+%F %H:%M:%S
"` -----kill current client thread-----"
>>
/etc/keepalived/logs/state_change
.log
rm
-f
/tmp/kill
.sql &>
/dev/null
###这里其实是一个批量kill线程的小技巧
mysql_con -e
'select concat("kill ",id,";") from information_schema.PROCESSLIST where command="Query" or command="Execute" into outfile "/tmp/kill.sql";'
mysql_con -e
"source /tmp/kill.sql"
2>>
/etc/keepalived/logs/state_change
.log
sleep
2
###给kill一个执行和缓冲时间
###确保DB1已经追上了,下面的repl为复制所用的账户,-h后跟DB1的内网IP
pos=`mysql -urepl -pxxxx -h192.168.1.x -e
"show slave status\G;"
|
grep
"Master_Log_Pos"
|
awk
'{printf ("%s",$NF "\t")}'
`
read_pos=`
echo
$pos|
awk
'{print $1}'
`
exec_pos=`
echo
$pos|
awk
'{print $2}'
`
until
[ $read_pos = $exec_pos ]
do
echo
-e
"`date "
+%F %H:%M:%S
"` -----DB1 Exec_Master_Log_Pos($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
192.168.1.x
'mysql -uxxxx -pxxxx -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"
|
/bin/mailx
-s
"DB2 keepalived change to BACKUP"
xxx@xxxx.com 2>>
/etc/keepalived/logs/state_change
.log
echo
-e
"@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@\n"
>>
/etc/keepalived/logs/state_change
.log
|
日志截图:
DB1 mysql服务故障:
DB1 mysql服务正常,查询失败:
DB2 一次切换过程:
DB2 执行脚本手动切回DB1:
总结:此方相比MHA或者MMM之类技术,特点在于简单,降低实施和维护复杂度;同时也安全的解决了主从中master节点的单点问题;在此基础上,亦可以再增加从库实现读写分离等架构;不足之处是双主仍是单活,DB2只是作为热备。
本文转自kai404 51CTO博客,原文链接:http://blog.51cto.com/kaifly/1665729,如需转载请自行联系原作者