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本文主要给大家简单讲讲MySQL高可用MHA讲析，相关专业术语大家可以上网查查或者找一些相关书籍补充一下，这里就不涉猎了，直奔主题，希望可以给大家带来一些实际帮助。
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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.d
Slave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.pm
2.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] 85154
6.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:172.16.75.4
7.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 mariadb
Manager：
[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；
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