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MHA（MySQL|Master High Availability）是一种基于主从模型的相当成熟的一种解决方案，我们对于master做一个高可用，使得哪怕在master数据库云服务器宕机时，我们的slave可以及时顶上，直接变成master主机，保证服务可靠的运行；
由于mha4mysql不存在于镜像仓库和epel中，所以需要下载rpm包，我下载的是
mha4mysql-manager-0.56-0.el6.noarch.rpm
mha4mysql-node-0.56-0.el6.noarch.rpm
建议mha服务器和master服务器分开；否则master物理宕机的话，mha也会宕机；
Master和slave上安装mha4mysql-node节点；
mha服务器两个rpm包都需要安装；
MHA： CentOS 7.5B 172.16.75.2
Master： CentOS 7.5D 172.16.75.4
Slave： CentOS 7.5C 172.16.75.3
三台主机都需要进行SSH免密通信；
因为如果master宕机，slave需要顶上，所以slave和master都需要开启二进制日志和中继日志；
Master配置文件：
[mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 # Settings user and group are ignored when systemd is used. # If you need to run mysqld under a different user or group, # customize your systemd unit file for mariadb according to the # instructions in http://fedoraproject.org/wiki/Systemd innodb_file_per_table=ON skip_name_resolve=ON server_id=401 log_bin=/var/lib/mysql/binlog sync_binlog=1 innodb_flush_log_at_trx_commit=1 relay_log_purge=0 relay_log=relay_log [mysqld_safe] log-error=/var/log/mariadb/mariadb.log pid-file=/var/run/mariadb/mariadb.pid # # include all files from the config directory # !includedir /etc/my.cnf.dSlave配置文件：
[mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 # Settings user and group are ignored when systemd is used. # If you need to run mysqld under a different user or group, # customize your systemd unit file for mariadb according to the # instructions in http://fedoraproject.org/wiki/Systemd innodb_file_per_table=ON skip_name_resolve=ON server_id=301 read_only=ON relay_log=slavelog relay_log_purge=0 log_bin=binlog [mysqld_safe] log-error=/var/log/mariadb/mariadb.log pid-file=/var/run/mariadb/mariadb.pid # # include all files from the config directory # !includedir /etc/my.cnf.d然后其他配置不变，搭建主从模型；
1.下载完mha的rpm包后，分别在对应的节点安装对应的安装包，通过查看mha4mysql-manager配置文件，全是二进制执行脚本。所以mha的配置文件需要自己写；
[root@slave1 ~]# rpm -ql mha4mysql-manager /usr/bin/masterha_check_repl /usr/bin/masterha_check_ssh /usr/bin/masterha_check_status /usr/bin/masterha_conf_host /usr/bin/masterha_manager /usr/bin/masterha_master_monitor /usr/bin/masterha_master_switch /usr/bin/masterha_secondary_check /usr/bin/masterha_stop /usr/share/man/man1/masterha_check_repl.1.gz /usr/share/man/man1/masterha_check_ssh.1.gz /usr/share/man/man1/masterha_check_status.1.gz /usr/share/man/man1/masterha_conf_host.1.gz /usr/share/man/man1/masterha_manager.1.gz /usr/share/man/man1/masterha_master_monitor.1.gz /usr/share/man/man1/masterha_master_switch.1.gz /usr/share/man/man1/masterha_secondary_check.1.gz /usr/share/man/man1/masterha_stop.1.gz /usr/share/perl5/vendor_perl/MHA/Config.pm /usr/share/perl5/vendor_perl/MHA/DBHelper.pm /usr/share/perl5/vendor_perl/MHA/FileStatus.pm /usr/share/perl5/vendor_perl/MHA/HealthCheck.pm /usr/share/perl5/vendor_perl/MHA/ManagerAdmin.pm /usr/share/perl5/vendor_perl/MHA/ManagerAdminWrapper.pm /usr/share/perl5/vendor_perl/MHA/ManagerConst.pm /usr/share/perl5/vendor_perl/MHA/ManagerUtil.pm /usr/share/perl5/vendor_perl/MHA/MasterFailover.pm /usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm /usr/share/perl5/vendor_perl/MHA/MasterRotate.pm /usr/share/perl5/vendor_perl/MHA/SSHCheck.pm /usr/share/perl5/vendor_perl/MHA/Server.pm /usr/share/perl5/vendor_perl/MHA/ServerManager.pm2.创建mha相对应的配置文件；
[root@slave1 ~]# mkdir /etc/mha [root@slave1 ~]# vim /etc/mha/app1.cnf [root@slave1 ~]# [root@slave1 ~]# cat /etc/mha/app1.cnf [server default] user=mha #登录用户 password=mhapass manager_workdir=/data/masterha/app1 manager_log=/data/masterha/app1/manager.log remote_workdir=/data/masterha/app1 ssh_user=root repl_user=repuser #master做replication slave授权的用户 repl_password=123456 ping_interval=1 [server1] hostname=172.16.75.4 candidate_master=1 [server2] hostname=172.16.75.3 candidate_master=1 [root@slave1 ~]# [root@slave1 ~]# mkdir -pv /data/masterha/app1 mkdir: 已创建目录 "/data" mkdir: 已创建目录 "/data/masterha" mkdir: 已创建目录 "/data/masterha/app1"3.根据配置文件内容，master还需要对mha做一个授权用户。
Master mysql：
MariaDB [(none)]> grant all on *.* to 'mha'@'%' identified by 'mhapass'; Query OK, 0 rows affected (0.08 sec)4.在mha服务器上进行ssh测试和repl测试（最后显示 OK即可）；
[root@slave1 ~]# masterha_check_ssh --conf=/etc/mha/app1.cnf Wed Nov 7 20:46:17 2018 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping. Wed Nov 7 20:46:17 2018 - [info] Reading application default configuration from /etc/mastermha/app1.cnf.. Wed Nov 7 20:46:17 2018 - [info] Reading server configuration from /etc/mastermha/app1.cnf.. Wed Nov 7 20:46:17 2018 - [info] Starting SSH connection tests.. Wed Nov 7 20:46:18 2018 - [debug] Wed Nov 7 20:46:17 2018 - [debug] Connecting via SSH from root@172.16.75.4(172.16.75.4:22) to root@172.16.75.3(172.16.75.3:22).. Wed Nov 7 20:46:17 2018 - [debug] ok. Wed Nov 7 20:46:18 2018 - [debug] Wed Nov 7 20:46:17 2018 - [debug] Connecting via SSH from root@172.16.75.3(172.16.75.3:22) to root@172.16.75.4(172.16.75.4:22).. Wed Nov 7 20:46:18 2018 - [debug] ok. Wed Nov 7 20:46:18 2018 - [info] All SSH connection tests passed successfully.[root@slave1 ~]# masterha_check_repl --conf=/etc/mha/app.cnf … 172.16.75.4(172.16.75.4:3306) (current master) +--172.16.75.3(172.16.75.3:3306) Thu Nov 8 09:37:35 2018 - [info] Checking replication health on 172.16.75.3.. Thu Nov 8 09:37:35 2018 - [info] ok. Thu Nov 8 09:37:35 2018 - [warning] master_ip_failover_script is not defined. Thu Nov 8 09:37:35 2018 - [warning] shutdown_script is not defined. Thu Nov 8 09:37:35 2018 - [info] Got exit code 0 (Not master dead). MySQL Replication Health is OK.5.启动mha4mysql进程；
[root@slave1 ~]# nohup masterha_manager --conf=/etc/mha/app.cnf > /data/masterha/app1/manager.log 2>&1 & [1] 851546.检测mha的状态；
[root@slave1 ~]# masterha_check_status --conf=/etc/mha/app.cnf app (pid:85154) is running(0:PING_OK), master:172.16.75.47.测试：
把master的mysql进程关掉；然后查看manager上的mha日志：
Master：
[root@slave2 ~]# systemctl stop mariadbManager：
[root@slave1 ~]# masterha_check_status --conf=/etc/mha/app.cnf app master is down and failover is running(50:FAILOVER_RUNNING). master:172.16.75.4 [root@slave1 ~]# cat /data/masterha/app1/manager.log … … ----- Failover Report ----- app: MySQL Master failover 172.16.75.4(172.16.75.4:3306) to 172.16.75.3(172.16.75.3:3306) succeeded Master 172.16.75.4(172.16.75.4:3306) is down! Check MHA Manager logs at slave1.ljy.com:/data/masterha/app1/manager.log for details. Started automated(non-interactive) failover. The latest slave 172.16.75.3(172.16.75.3:3306) has all relay logs for recovery. Selected 172.16.75.3(172.16.75.3:3306) as a new master. 172.16.75.3(172.16.75.3:3306): OK: Applying all logs succeeded. Generating relay diff files from the latest slave succeeded. 172.16.75.3(172.16.75.3:3306): Resetting slave info succeeded. Master failover to 172.16.75.3(172.16.75.3:3306) completed successfully.最后，当出现Master failover to 172.16.75.3(172.16.75.3:3306) completed successfully.
就意味着我们的master已经转到slave上了，虽然之前的Master数据库服务器down掉，但是我们通过mha及时的切换到slave主机上，保证数据库服务器的可靠性。
遇到的大坑：Checking if super_read_only is defined and turned on..DBD::mysql::st execute failed: Unknown system variable 'super_read_only' at /usr/share/perl5/vendor_perl/MHA/SlaveUtil.pm line 245.
一开始用的0.58版本的mha，结果在进行repl检测的时候，出现了“super read only”的错误，这是因为我们的mysql版本和mha版本有不兼容的情况，换用0.56的版本就可以，因为0.58版本的mha兼容的是mariadb-10以后版本有”super_read_only”选项，我们正常CentOS-7系列主机上安装的MariaDB-5.56没有”super_read_only”选项，所以检测repl权限时，会说我们没有设置此选项；
总之，mha在生产环境中有很高的必要性，我们需要Proxysql做读写分离提升服务器性能的同时，又需要mha对master做高可用来保证服务器的可靠性，保障我们的数据库不间断的运行；
MySQL高可用MHA讲析就先给大家讲到这里，对于其它相关问题大家想要了解的可以持续关注我们的行业资讯。我们的板块内容每天都会捕捉一些行业新闻及专业知识分享给大家的。
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