MYSQL数据库的主从切换
一、MHA简介
MHA（Master High Availability）目前在MySQL高可用方面是一个相对成熟的解决方案，它由日本DeNA公司的youshimaton（现就职于 Facebook公司）开发，是一套优秀的作为MySQL高可用性环境下故障切换和主从提升的高可用软件。在MySQL故障切换过程中，MHA能做到在 0~30秒之内自动完成数据库的故障切换操作，并且在进行故障切换的过程中，MHA能在最大程度上保证数据的一致性，以达到真正意义上的高可用。
该软件由两部分组成：MHA Manager（管理节点）和MHA Node（数据节点）。MHA Manager可以单独部署在一台独立的机器上管理多个master-slave集群，也可以部署在一台slave节点上。MHA Node运行在每台MySQL服务器上，MHA Manager会定时探测集群中的master节点，当master出现故障时，它可以自动将最新数据的slave提升为新的master，然后将所有其 他的slave重新指向新的master。整个故障转移过程对应用程序完全透明。
在MHA自动故障切换过程中，MHA试图从宕机的主服务器上保存二进制日志，最大程度的保证数据的不丢失，但这并不总是可行的。例如，如果主服务器硬件故 障或无法通过ssh访问，MHA没法保存二进制日志，只进行故障转移而丢失了最新的数据。使用MySQL 5.5的半同步复制，可以大大降低数据丢失的风险。MHA可以与半同步复制结合起来。如果只有一个slave已经收到了最新的二进制日志，MHA可以将最 新的二进制日志应用于其他所有的slave服务器上，因此可以保证所有节点的数据一致性。
MHA框架图
MHA工作原理总结为以下几条：
- 从宕机崩溃的master保存二进制日志事件（binlog events）；
- 识别含有最新更新的slave；
- 应用差异的中继日志（relay log）到其他slave；
- 应用从master保存的二进制日志事件（binlog events）；
- 提升一个slave为新master；
- 使用其他的slave连接新的master进行复制。
二、MHA安装配置
实验环境： 一主两从的主从复制
server1 主库
server2 从库
server3 从库
server4 manager
首先将数据库配置成基于gtid下一主二从且半同步，主意这里半同步不要直接写入配置文件，在登录mysql后可手动添加，mysql的主从复制查看前面的博客，这里不再鳌述。
这里是三个配置文件里写入的内容，不写入半同步，三个库的server_id不同
MHA配置
在server4上安装MHA软件包
分别在三个库安装node软件包
在managr中编辑配置文件
首先建立该目录
配置节点互相ssh免密登陆
在server4，manager节点生成key并分发给所有用户
[root@server4 ~]# cd .ssh/
[root@server4 .ssh]# ls
known_hosts
[root@server4 .ssh]# ssh-keygen
[root@server4 .ssh]# ls
id_rsa id_rsa.pub known_hosts
[root@server4 .ssh]# cd
[root@server4 ~]# scp -r .ssh/ server1:
root@server1's password:
known_hosts 100% 540 0.5KB/s 00:00
id_rsa 100% 1679 1.6KB/s 00:00
id_rsa.pub 100% 394 0.4KB/s 00:00
[root@server4 ~]# scp -r .ssh/ server2:
root@server2's password:
known_hosts 100% 540 0.5KB/s 00:00
id_rsa 100% 1679 1.6KB/s 00:00
id_rsa.pub 100% 394 0.4KB/s 00:00
[root@server4 ~]# scp -r .ssh/ server3:
root@server3's password:
known_hosts 100% 540 0.5KB/s 00:00
id_rsa 100% 1679 1.6KB/s 00:00
id_rsa.pub 100% 394 0.4KB/s 00:00
[root@server4 ~]# ssh-copy-id server1
[root@server4 ~]# ssh-copy-id server2
[root@server4 ~]# ssh-copy-id server3检测：
ssh检测successful，没有错误
重新启动mysql
主库登录，给权限，并刷新授权表
两个从库登录，写入只读
调度器repl检测ok，没有错误
[root@server4 ~]# masterha_check_ssh --conf=/etc/masterha/app1.cnf
Wed Feb 27 11:05:24 2019 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Wed Feb 27 11:05:24 2019 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
Wed Feb 27 11:05:24 2019 - [info] Reading server configuration from /etc/masterha/app1.cnf..
Wed Feb 27 11:05:24 2019 - [info] Starting SSH connection tests..
Wed Feb 27 11:05:24 2019 - [debug]
Wed Feb 27 11:05:24 2019 - [debug] Connecting via SSH from [email protected](172.25.254.1:22) to [email protected](172.25.254.2:22)..
Wed Feb 27 11:05:24 2019 - [debug] ok.
Wed Feb 27 11:05:24 2019 - [debug] Connecting via SSH from [email protected](172.25.254.1:22) to [email protected](172.25.254.3:22)..
Warning: Permanently added '172.25.254.3' (ECDSA) to the list of known hosts.
Wed Feb 27 11:05:24 2019 - [debug] ok.
Wed Feb 27 11:05:25 2019 - [debug]
Wed Feb 27 11:05:24 2019 - [debug] Connecting via SSH from [email protected](172.25.254.2:22) to [email protected](172.25.254.1:22)..
Wed Feb 27 11:05:25 2019 - [debug] ok.
Wed Feb 27 11:05:25 2019 - [debug] Connecting via SSH from [email protected](172.25.254.2:22) to [email protected](172.25.254.3:22)..
Warning: Permanently added '172.25.254.3' (ECDSA) to the list of known hosts.
Wed Feb 27 11:05:25 2019 - [debug] ok.
Wed Feb 27 11:05:25 2019 - [debug]
Wed Feb 27 11:05:25 2019 - [debug] Connecting via SSH from [email protected](172.25.254.3:22) to [email protected](172.25.254.1:22)..
Wed Feb 27 11:05:25 2019 - [debug] ok.
Wed Feb 27 11:05:25 2019 - [debug] Connecting via SSH from [email protected](172.25.254.3:22) to [email protected](172.25.254.2:22)..
Wed Feb 27 11:05:25 2019 - [debug] ok.
Wed Feb 27 11:05:25 2019 - [info] All SSH connection tests passed successfully.
[root@server4 ~]# masterha_check_repl --conf=/etc/masterha/app1.cnf
Wed Feb 27 11:13:44 2019 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Wed Feb 27 11:13:44 2019 - [info] Reading application default configuration from /etc/masterha/app1.cnf..
Wed Feb 27 11:13:44 2019 - [info] Reading server configuration from /etc/masterha/app1.cnf..
Wed Feb 27 11:13:44 2019 - [info] MHA::MasterMonitor version 0.58.
Wed Feb 27 11:13:45 2019 - [info] GTID failover mode = 1
Wed Feb 27 11:13:45 2019 - [info] Dead Servers:
Wed Feb 27 11:13:45 2019 - [info] Alive Servers:
Wed Feb 27 11:13:45 2019 - [info] 172.25.254.1(172.25.254.1:3306)
Wed Feb 27 11:13:45 2019 - [info] 172.25.254.2(172.25.254.2:3306)
Wed Feb 27 11:13:45 2019 - [info] 172.25.254.3(172.25.254.3:3306)
Wed Feb 27 11:13:45 2019 - [info] Alive Slaves:
Wed Feb 27 11:13:45 2019 - [info] 172.25.254.2(172.25.254.2:3306) Version=5.7.24-log (oldest major version between slaves) log-bin:enabled
Wed Feb 27 11:13:45 2019 - [info] GTID ON
Wed Feb 27 11:13:45 2019 - [info] Replicating from 172.25.254.1(172.25.254.1:3306)
Wed Feb 27 11:13:45 2019 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Feb 27 11:13:45 2019 - [info] 172.25.254.3(172.25.254.3:3306) Version=5.7.24-log (oldest major version between slaves) log-bin:enabled
Wed Feb 27 11:13:45 2019 - [info] GTID ON
Wed Feb 27 11:13:45 2019 - [info] Replicating from 172.25.254.1(172.25.254.1:3306)
Wed Feb 27 11:13:45 2019 - [info] Not candidate for the new Master (no_master is set)
Wed Feb 27 11:13:45 2019 - [info] Current Alive Master: 172.25.254.1(172.25.254.1:3306)
Wed Feb 27 11:13:45 2019 - [info] Checking slave configurations..
Wed Feb 27 11:13:45 2019 - [info] Checking replication filtering settings..
Wed Feb 27 11:13:45 2019 - [info] binlog_do_db= , binlog_ignore_db=
Wed Feb 27 11:13:45 2019 - [info] Replication filtering check ok.
Wed Feb 27 11:13:45 2019 - [info] GTID (with auto-pos) is supported. Skipping all SSH and Node package checking.
Wed Feb 27 11:13:45 2019 - [info] Checking SSH publickey authentication settings on the current master..
Wed Feb 27 11:13:45 2019 - [info] HealthCheck: SSH to 172.25.254.1 is reachable.
Wed Feb 27 11:13:45 2019 - [info]
172.25.254.1(172.25.254.1:3306) (current master)
+--172.25.254.2(172.25.254.2:3306)
+--172.25.254.3(172.25.254.3:3306)
Wed Feb 27 11:13:45 2019 - [info] Checking replication health on 172.25.254.2..
Wed Feb 27 11:13:45 2019 - [info] ok.
Wed Feb 27 11:13:45 2019 - [info] Checking replication health on 172.25.254.3..
Wed Feb 27 11:13:45 2019 - [info] ok.
Wed Feb 27 11:13:45 2019 - [warning] master_ip_failover_script is not defined.
Wed Feb 27 11:13:45 2019 - [warning] shutdown_script is not defined.
Wed Feb 27 11:13:45 2019 - [info] Got exit code 0 (Not master dead).
MySQL Replication Health is OK.
测试：
手动测试：当主库server1宕机，在server4进行手动切换
server4手动切换，down掉的主机是172.25.254.1，新的master是172.25.254.2
在server3从库查看，新的master是172.25.254.2
重新启动server1将其加入到数据库的备库
二、在主机不宕机时，进行切换
首先查看masterha，看是否生成文件app1.failover.complete，生成的话，要将其删除掉
在server4进行手动不宕机切换
在server2查看新的主库是server1
在server3查看主库server1
飘逸pid主从切换
编辑配置文件打开pid注释
在/usr/local/bin/目录下拷贝老师的脚本
编辑两个脚本进行修改
给脚本执行权限
在主库建立虚拟ip（目前主库在server1）
调度器手动执行切换
主库从172.25.254.1 切换到172.25.254.2
在172.25.254.1和172.25.254.2查看飘逸的ip
server1的虚拟ip不见了
server2上出现新的虚拟ip
server3查看目前的主库为172.25.254.2
自动切换
在server4上执行自动切换
目前主库在server2
当停止主库会切换到新的server1主库
在server1查看新的飘逸来的ip
在server2查看ip，虚拟ip不见了，发生主从切换
恢复server2为从库
