keepalived+mysql雙主原理：
（1）主庫1上的keepalived啟動之后，會檢查mysql服務(wù)是否活著，如果活著，keepalived進(jìn)入master狀態(tài)，獲得VIP；
（2）主庫2上的keepalived啟動之后，也會檢查mysql是否活著，然后檢查keepalived組內(nèi)是否有master狀態(tài)，如果有，則主庫2上的keepalived進(jìn)入backup狀態(tài)，處于隨時接管VIP狀態(tài)；
（3）如果主庫1上的mysql掛了，keepalived進(jìn)入fault狀態(tài)，釋放VIP，主庫2上的keepalived會變成master狀態(tài)，獲得VIP；
實驗環(huán)境：
OS：CentOS release 6.6 (Final)
數(shù)據(jù)庫：mysql 5.7.14
A: master ：192.168.91.23
B: slave ：192.168.91.22
VIP：192.168.91.100
操作系統(tǒng)時間一致更改：
date -s "20170227 16:25"
hwclock --systohc
主從參數(shù)：
A：
server_id = 330623
gtid_mode=ON
log_slave_updates = 0
enforce_gtid_consistency = ON
auto_increment_offset =1
auto_increment_increment =2
B：
server_id = 330622
gtid_mode=ON
log_slave_updates = 0
enforce_gtid_consistency = ON
auto_increment_offset=2
auto_increment_increment=2
配置AB互為主從：
A：
創(chuàng)建復(fù)制賬戶：
create user rep@'192.168.91.%' identified by '147258';
grant replication slave on *.* to rep@'192.168.91.%';
把A做個全備，還原到B上（這里省略不寫）
B：添加A為B的主庫：
change master to master_host='192.168.91.23', master_port=3306, master_user='rep',master_password='147258', master_auto_position=1;
start slave；
A：添加B為A的主庫：
change master to master_host='192.168.91.22', master_port=3306, master_user='rep',master_password='147258', master_auto_position=1;
start slave；
創(chuàng)建一個監(jiān)控賬戶：（后面checkMySQL.py 腳本會用到，用于檢測mysql數(shù)據(jù)庫狀態(tài)，這個用戶只要有usage權(quán)限即可）
GRANT REPLICATION CLIENT ON *.* TO 'monitor'@'%' IDENTIFIED BY 'm0n1tor';
Ａ和Ｂ都要安裝keepalived軟件：
yum install keepalived -y
yum install MySQL-python -y
A的keepalived配置文件：
[root@Darren1 keepalived]#cat << EOF > keepalived.conf
vrrp_script vs_mysql_23 { #可以根據(jù)實際情況命名
script "/etc/keepalived/checkMySQL.py -h 192.168.91.23 -P 3306"
interval 60 #切換時間
}
vrrp_instance VI_23 { #可以根據(jù)實際情況命名
state BACKUP #剛開始時使其處于backup狀態(tài)
nopreempt #設(shè)置為不搶占，m1掛了，m2接管VIP,m1重啟不會自動搶回VIP
interface eth0 #VIP用的網(wǎng)卡
virtual_router_id 23 #路由id，范圍是0-255，不能和路由器高可用的id一樣，同一集群中該數(shù)值要相同
priority 100 #優(yōu)先級，同一個vrrp_instance的MASTER優(yōu)先級必須比BACKUP高。
advert_int 5
authentication {
auth_type PASS #認(rèn)證加密
auth_pass 1111 # 認(rèn)證密碼，但密碼不要超過 8 位
}
track_script {
vs_mysql_23 #調(diào)用這個腳本，返回0就持有VIP，返回1就釋放VIP
}
virtual_ipaddress {
192.168.11.100 #VIP地址
}
}
EOF
B配置文件：
[root@Darren2 keepalived]# cat << EOF > keepalived.conf
vrrp_script vs_mysql_22 {
script "/etc/keepalived/checkMySQL.py -h 192.168.91.22 -P 3306" #此處和A不同，其他都相同
interval 60
}
vrrp_instance VI_22 {
state BACKUP
nopreempt
interface eth0
virtual_router_id 23
priority 90
advert_int 5
authentication {
auth_type PASS
auth_pass 1111
}
track_script {
vs_mysql_22
}
virtual_ipaddress {
192.168.91.100
}
}
EOF
checkMySQL.py腳本作用（這里省略不寫）：
腳本的作用是判斷mysql進(jìn)程是否存在，如果存在返回0，如果不存在返回1；
A和B啟用keepalived
/etc/init.d/keepalived start （開始開的時候，A和B誰先啟動，VIP就先在誰上）
chkconfig –level 2345 keepalived on
keepalived啟動過程：
此時A開啟keepalived服務(wù)：
[root@Darren1 ~]# /etc/init.d/keepalived start
[root@Darren1 ~]# tail -f /var/log/messages
May 9 14:41:05 Darren1 Keepalived[28172]: Starting Keepalived v1.2.13 (03/19,2015)
May 9 14:41:05 Darren1 Keepalived[28173]: Starting Healthcheck child process, pid=28175
May 9 14:41:05 Darren1 Keepalived[28173]: Starting VRRP child process, pid=28176
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Netlink reflector reports IP 192.168.91.23 added
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Netlink reflector reports IP 192.168.91.23 added
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Netlink reflector reports IP fe80::20c:29ff:fe56:5380 added
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Registering Kernel netlink reflector
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Registering Kernel netlink command channel
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Registering gratuitous ARP shared channel
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Opening file '/etc/keepalived/keepalived.conf'.
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Netlink reflector reports IP fe80::20c:29ff:fe56:5380 added
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Registering Kernel netlink reflector
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Registering Kernel netlink command channel
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Opening file '/etc/keepalived/keepalived.conf'.
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Configuration is using : 62873 Bytes
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: Using LinkWatch kernel netlink reflector...
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Entering BACKUP STATE
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Configuration is using : 5173 Bytes
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: VRRP sockpool: [ifindex(2), proto(112), unicast(0), fd(10,11)]
May 9 14:41:05 Darren1 Keepalived_healthcheckers[28175]: Using LinkWatch kernel netlink reflector...
May 9 14:41:05 Darren1 Keepalived_vrrp[28176]: VRRP_Script(vs_mysql_23) succeeded
May 9 14:41:21 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Transition to MASTER STATE
May 9 14:41:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Entering MASTER STATE
May 9 14:41:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) setting protocol VIPs.
May 9 14:41:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Sending gratuitous ARPs on eth0 for 192.168.91.100
May 9 14:41:26 Darren1 Keepalived_healthcheckers[28175]: Netlink reflector reports IP 192.168.91.100 added
May 9 14:41:31 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Sending gratuitous ARPs on eth0 for 192.168.91.100
總結(jié)啟動過程：
（1）啟動keepalived三個進(jìn)程，分別是主進(jìn)程，健康檢查子進(jìn)程，VRRP協(xié)議子進(jìn)程；
（2）啟動結(jié)束后，VRRP_Instance開始進(jìn)入backup狀態(tài)；
（3）進(jìn)入backup成功后，VRRP_Instance轉(zhuǎn)變狀態(tài)為master，然后進(jìn)入master狀態(tài)；
（4）獲取VIP，并且用ARP廣播告訴其他服務(wù)器；
keepalived切換過程：
停止A的mysql服務(wù)：
[root@Darren1 ~]# /etc/init.d/mysqld stop
Shutting down MySQL............ SUCCESS!
此時A的變化：
[root@Darren1 ~]# tail -f /var/log/messages
May 9 14:43:25 Darren1 Keepalived_vrrp[28176]: VRRP_Script(vs_mysql_23) failed
May 9 14:43:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Entering FAULT STATE
May 9 14:43:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) removing protocol VIPs.
May 9 14:43:26 Darren1 Keepalived_vrrp[28176]: VRRP_Instance(VI_23) Now in FAULT state
May 9 14:43:26 Darren1 Keepalived_healthcheckers[28175]: Netlink reflector reports IP 192.168.91.100 removed
總結(jié)A的變化：VRRP_Instance進(jìn)入fault狀態(tài)，釋放VIP；
此時B的變化：
[root@Darren2 ~]# tail -f /var/log/messages
May 9 14:43:26 Darren2 Keepalived_vrrp[35138]: VRRP_Instance(VI_22) Transition to MASTER STATE
May 9 14:43:31 Darren2 Keepalived_vrrp[35138]: VRRP_Instance(VI_22) Entering MASTER STATE
May 9 14:43:31 Darren2 Keepalived_vrrp[35138]: VRRP_Instance(VI_22) setting protocol VIPs.
May 9 14:43:31 Darren2 Keepalived_vrrp[35138]: VRRP_Instance(VI_22) Sending gratuitous ARPs on eth0 for 192.168.91.100
May 9 14:43:31 Darren2 Keepalived_healthcheckers[35137]: Netlink reflector reports IP 192.168.91.100 added
May 9 14:43:36 Darren2 Keepalived_vrrp[35138]: VRRP_Instance(VI_22) Sending gratuitous ARPs on eth0 for 192.168.91.100
總結(jié)B的變化：VRRP_Instance進(jìn)入master狀態(tài)，獲得VIP，ARP廣播通知；
使用VIP登陸數(shù)據(jù)庫：
創(chuàng)建登陸用戶：
create user 'keepalived'@'%' identified by '147258';
grant all on *.* to 'keepalived'@'%';
此時VIP在B上：
[root@Darren2 ~]# ip addr |grep 192
inet 192.168.91.22/24 brd 192.168.91.255 scope global eth0
inet 192.168.91.100/32 scope global eth0
在A上用'keepalived'@'%'賬戶登陸，是可以登陸成功的，證明此VIP是有效的：
[root@Darren1 ~]# mysql -ukeepalived -p147258 -h292.168.91.100
keepalived@192.168.91.100 [(none)]>select user(),current_user();
+--------------------------+----------------+
| user() | current_user() |
+--------------------------+----------------+
| keepalived@192.168.91.23 | keepalived@% |
+--------------------------+----------------+
總結(jié)：
幾種VIP切換情況：
（1）m1主機(jī)宕機(jī)，VIP會切換到m2;
（2）m1上的mysql掛了，VIP會切換到m2;
（3）m1上的keepalived服務(wù)掛了，又分為兩種情況：
/etc/init.d/keepalived stop：正常切換
kill -9 keepalived_pid：因為keepalived是直接退出，m1和m2都有VIP,但是連接時候只有一個是生效的；
（4）腦裂的情況，m1和m2都各自認(rèn)為自己是master狀態(tài)，搶占VIP，VIP一會在m1上，一會在m2上；
在同一個交換機(jī)下不存在腦裂情況，這個在比較復(fù)雜的網(wǎng)絡(luò)環(huán)境中會發(fā)生。
可以在腳本中防范：ping一下網(wǎng)關(guān)，如果連網(wǎng)關(guān)都ping不通，vrrp_script腳本就放回1，keepalived進(jìn)入fault狀態(tài)；
m1掛了，m2接管VIP，m1修復(fù)好了之后怎么辦？
（1）如果是GTID復(fù)制直接把m1change master to m2上，如果是傳統(tǒng)復(fù)制，需要找到binlog位置；
（2）等待m1同步完成；
（3）啟動keepalived；
keepalived+mysql雙主缺點和對應(yīng)方法：
（1）數(shù)據(jù)庫一致性難保障：
可以使用增強(qiáng)半同步，把主庫等待從庫回應(yīng)的參數(shù)rpl_semi_sync_master_timeout 調(diào)大點，
出現(xiàn)master的日志沒能實時的傳到slave上，需要手工把binlog截取出來補(bǔ)到從庫上；如果系統(tǒng)不存在了，可以通過binlog server 補(bǔ)日志；
（2）需要手動把出現(xiàn)故障的主庫加入到原來的結(jié)構(gòu)中；
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