MHA是一种方便简单可靠的MySQL高可用架构，具体的介绍我在这里就不多说了，下面是我在网上找的一个教程，我在此基础上进行了一些修改：

大致步骤

（一）、环境介绍
（二）、用ssh-keygen实现四台主机之间相互免密钥登录
（三）、安装MHAmha4mysql-node，mha4mysql-manager和perl环境包
（四）、建立master，slave1，slave2之间主从复制
（五）、管理机manager上配置MHA文件
（六）、masterha_check_ssh工具验证ssh信任登录是否成功
（七）、masterha_check_repl工具验证mysql复制是否成功
（八）、启动MHA manager,并监控日志文件
（九）、测试master宕机后，是否会自动切换 

（一）环境介绍

1.主机部署

CentOS 7改主机名

hostnamectl set-hostname master

192.168.56.121    master
192.168.56.122    slave1    #备用master
192.168.56.123    slave2    
192.168.56.124    manager 

将ip和域名配置到/etc/hosts文件中

尝试在各主机上的防火墙上加上端口的允许

iptables -I INPUT -s 0/0 -p tcp --dport 3306 -j ACCEPT 

这条规则的意思是，想要在输入数据INPUT中，protocol为tcp/IP的方式，访问端口3306，都会被允许的

iptables -L -n|grep 3306
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:3306 

（二）用ssh-keygen实现四台主机之间相互免密钥登录

1.生成密钥

[master，slave1，slave2，manager]

ssh-keygen -t rsa 

[slave1,slave2,manager]

scp .ssh/id_rsa.pub master:/root/.ssh/slave1.pub 
scp .ssh/id_rsa.pub master:/root/.ssh/slave2.pub
scp .ssh/id_rsa.pub master:/root/.ssh/manager.pub 

2.在主机上用cat xxx >> authorized_keys导入公钥到/root/.ssh/authorized_keys文件中

[master]

cat ~/.ssh/*.pub>>~/.ssh/authorized_keys
scp ~/.ssh/authorized_keys slave1:/root/.ssh/authorized_keys 
scp ~/.ssh/authorized_keys slave2:/root/.ssh/authorized_keys 
scp ~/.ssh/authorized_keys manager:/root/.ssh/authorized_keys 

（三）安装MHAmha4mysql-node，mha4mysql-manager 软件包

1.安装MHAmha4mysql-node

[manager,master,slave1,slave2]

yum -y install perl-DBD-MySQL
yum -y install perl-Config-Tiny    
yum -y install perl-Log-Dispatch    
yum -y install perl-Parallel-ForkManager
mha4mysql-node-0.55-0.el6.noarch.rpm 

2.安装mha4mysql-manager

[manager]

 yum -y install perl
 yum -y install cpan
 rpm -ivh mha4mysql-manager-0.55-0.el6.noarch.rpm 

缺啥，yum install xxx 啥就行。

（四）、建立master，slave1，slave2之间主从复制

略 

（五）、管理机manager上配置MHA文件

[manager] 

1.创建目录

mkdir -p /masterha/app1
mkdir /etc/masterha
vi /etc/masterha/app1.cnf

[server default]
user=root
password=root
manager_workdir=/masterha/app1
manager_log=/masterha/app1/manager.log
remote_workdir=/masterha/app1
ssh_user=root
repl_user=rep
repl_password=repl
ping_interval=1
[server1]
hostname=192.168.56.122
master_binlog_dir=/var/lib/mysql
candidate_master=1
#relay_log_purge=0
[server2]
hostname=192.168.56.121
master_binlog_dir=/var/lib/mysql
candidate_master=1
[server3]
hostname=192.168.56.123
master_binlog_dir=/var/lib/mysql
no_master=1
#relay_log_purge=0 

（六）、masterha_check_ssh工具验证ssh信任登录是否成功

[manager]

masterha_check_ssh --conf=/etc/masterha/app1.cnf
[root@manager ~]# masterha_check_ssh --conf=/etc/masterha/app1.cnf
Thu Feb 23 12:00:24 2017 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Thu Feb 23 12:00:24 2017 - [info] Reading application default configurations from /etc/masterha/app1.cnf..
Thu Feb 23 12:00:24 2017 - [info] Reading server configurations from /etc/masterha/app1.cnf..
Thu Feb 23 12:00:24 2017 - [info] Starting SSH connection tests..
Thu Feb 23 12:00:25 2017 - [debug] 
Thu Feb 23 12:00:24 2017 - [debug]  Connecting via SSH from root@192.168.56.122(192.168.56.122:22) to root@192.168.56.121(192.168.56.121:22)..
Thu Feb 23 12:00:25 2017 - [debug]   ok.
Thu Feb 23 12:00:25 2017 - [debug]  Connecting via SSH from root@192.168.56.122(192.168.56.122:22) to root@192.168.56.123(192.168.56.123:22)..
Thu Feb 23 12:00:25 2017 - [debug]   ok.
Thu Feb 23 12:00:25 2017 - [debug] 
Thu Feb 23 12:00:25 2017 - [debug]  Connecting via SSH from root@192.168.56.121(192.168.56.121:22) to root@192.168.56.122(192.168.56.122:22)..
Warning: Permanently added '192.168.56.121' (ECDSA) to the list of known hosts.
Thu Feb 23 12:00:25 2017 - [debug]   ok.
Thu Feb 23 12:00:25 2017 - [debug]  Connecting via SSH from root@192.168.56.121(192.168.56.121:22) to root@192.168.56.123(192.168.56.123:22)..
Thu Feb 23 12:00:25 2017 - [debug]   ok.
Thu Feb 23 12:00:26 2017 - [debug] 
Thu Feb 23 12:00:25 2017 - [debug]  Connecting via SSH from root@192.168.56.123(192.168.56.123:22) to root@192.168.56.122(192.168.56.122:22)..
Warning: Permanently added '192.168.56.123' (ECDSA) to the list of known hosts.
Thu Feb 23 12:00:26 2017 - [debug]   ok.
Thu Feb 23 12:00:26 2017 - [debug]  Connecting via SSH from root@192.168.56.123(192.168.56.123:22) to root@192.168.56.121(192.168.56.121:22)..
Thu Feb 23 12:00:26 2017 - [debug]   ok.
Thu Feb 23 12:00:26 2017 - [info] All SSH connection tests passed successfully.
[root@manager ~]# 

（七）、masterha_check_repl工具验证mysql复制是否成功

[manager]

masterha_check_repl --conf=/etc/masterha/app1.cnf

[root@manager mysql]# masterha_check_repl --conf=/etc/masterha/app1.cnf
Thu Feb 23 14:37:05 2017 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Thu Feb 23 14:37:05 2017 - [info] Reading application default configurations from /etc/masterha/app1.cnf..
Thu Feb 23 14:37:05 2017 - [info] Reading server configurations from /etc/masterha/app1.cnf..
Thu Feb 23 14:37:05 2017 - [info] MHA::MasterMonitor version 0.55.
Thu Feb 23 14:37:05 2017 - [info] Dead Servers:
Thu Feb 23 14:37:05 2017 - [info] Alive Servers:
Thu Feb 23 14:37:05 2017 - [info]   master(192.168.56.121:3306)
Thu Feb 23 14:37:05 2017 - [info]   slave1(192.168.56.122:3306)
Thu Feb 23 14:37:05 2017 - [info]   slave2(192.168.56.123:3306)
Thu Feb 23 14:37:05 2017 - [info] Alive Slaves:

.......此处省略

Thu Feb 23 14:37:08 2017 - [info]   Connecting to root@192.168.56.123(slave2:22).. 
Creating directory /masterha/app1.. done.
  Checking slave recovery environment settings..
    Opening /var/lib/mysql/relay-log.info ... ok.
    Relay log found at /tmp, up to mysql-relay-bin.000004
    Temporary relay log file is /tmp/mysql-relay-bin.000004
    Testing mysql connection and privileges..Warning: Using a password on the command line interface can be insecure.
 done.
    Testing mysqlbinlog output.. done.
    Cleaning up test file(s).. done.
Thu Feb 23 14:37:08 2017 - [info] Slaves settings check done.
Thu Feb 23 14:37:08 2017 - [info] 
master (current master)
 +--slave1
 +--slave2

Thu Feb 23 14:37:08 2017 - [info] Checking replication health on slave1..
Thu Feb 23 14:37:08 2017 - [info]  ok.
Thu Feb 23 14:37:08 2017 - [info] Checking replication health on slave2..
Thu Feb 23 14:37:08 2017 - [info]  ok.
Thu Feb 23 14:37:08 2017 - [warning] master_ip_failover_script is not defined.
Thu Feb 23 14:37:08 2017 - [warning] shutdown_script is not defined.
Thu Feb 23 14:37:08 2017 - [info] Got exit code 0 (Not master dead).

MySQL Replication Health is OK. 

（八）、启动MHA manager,并监控日志文件

[manager]

masterha_manager --conf=/etc/masterha/app1.cnf 
tail -f /masterha/app1/manager.log 

（九）测试master(宕机后，是否会自动切换

1.停掉master上的mysql服务

[master]

[root@master ~]# service mysql stop
Shutting down MySQL..... SUCCESS! 
[root@master ~]# 
[manager] 

2.宕掉master后，/masterha/app1/manager.log文件显示：

tail -f /masterha/app1/manager.log 

日志文件显示：

----- Failover Report -----

app1: MySQL Master failover master to slave1 succeeded

Master master is down!

Check MHA Manager logs at manager:/masterha/app1/manager.log for details.

Started automated(non-interactive) failover.
The latest slave slave1(192.168.56.122:3306) has all relay logs for recovery.
Selected slave1 as a new master.
slave1: OK: Applying all logs succeeded.
slave2: This host has the latest relay log events.
Generating relay diff files from the latest slave succeeded.
slave2: OK: Applying all logs succeeded. Slave started, replicating from slave1.
slave1: Resetting slave info succeeded.
Master failover to slave1(192.168.56.122:3306) completed successfully. 

上面的结果表明master成功切换。

切换过程中需要关注的几个问题

1.切换过程会自动把read_only关闭

2.切换之后需要删除手工删除/masterha/app1/app1.failover.complete，才能进行第二次测试

3.一旦发生切换管理进程将会退出，无法进行再次测试，需将故障数据库加入到MHA环境中来

4.原主节点重新加入到MHA时只能设置为slave,在

change master to master_host='192.168.56.122',
master_user='repl',
master_password='repl',
master_log_file='mysql-bin.000010',
master_log_pos=120; 

之前需要先 reset slave

5.关于ip地址的接管有几种方式，这里采用的是MHA自动调用IP别名的方式，好处是在能够保证数据库状态与业务IP切换的一致性。启动管理节点 之后 VIP会自动别名到当前主节点上，Keepalived也只能做到对3306的健康检查，但是做不到比如像MySQL复制中的Slave-SQL、 Slave-IO进程的检查，容易出现对切换的误判。

6.注意：二级从服务器需要将log_slave_updates打开

7.手工切换需要先定义好master_ip_online_change_script脚本,不然只会切换mysql,IP地址不会绑定上去，可以根据模板来配置该脚本

8.通过设置no_master=1可以让某一个节点永远不成为新的主节点

恢复集群运行

①在manager上删除app1.failover.complete文件

cd /masterha/app1
rm -f app1.failover.complete 

②原master主节点服务启动

service mysql start 

③ manager管理节点，检查同步报错

masterha_check_repl --conf=/etc/masterha/app1.cnf
Thu Feb 23 15:00:56 2017 - [error][/usr/share/perl5/vendor_perl/MHA/ServerManager.pm, ln604] There are 2 non-slave servers! MHA manages at most one non-slave server. Check configurations. 

⑤查看现在的slave1上的信息

mysql> show master status/G
*************************** 1. row ***************************
             File: mysql-bin.000010
         Position: 120
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 
1 row in set (0.00 sec) 

④配置187节点mysql为新的slave，并启动同步进程

change master to master_host='192.168.56.122',
master_user='repl',
master_password='repl',
master_log_file='mysql-bin.000010',
master_log_pos=120;
mysql> start slave; 

再次在管理节点上检查同步状态成功：

masterha_check_repl --conf=/etc/masterha/app1.cnf 

需注意：按如上步骤操作后，此时121节点作为slaver已加入到集群中，但是宕机这段时间122、123中新产生的数据在121中没有，所以还需要先从主节点备份导入最新的数据再启动同步

⑤启动MHA
nohup masterha_manager –conf=/etc/masterha/app1.cnf > /mha/app1/mha_manager.log &1 &

回切：
同样的道理，以上步骤配置无问题的话停止当前master的MySQL进程，MHA可直接切换master至原节点