MHA分管理节点和数据库节点，数据库节点由mysql主从或者主主从构成，当主库挂掉后，管理节点会自动将从节点提升为主节点；管理节点的角色类似于oracle数据库中的
MHA分管理节点和数据库节点，香港空间，数据库节点由mysql主从或者主主从构成，当主库挂掉后，管理节点会自动将从节点提升为主节点；管理节点的角色类似于oracle数据库中的fast start failover中的observer，但mha上层可以通过keepalive部署VIP，程序连接数据库使用VIP，从而实现后台数据库的故障切换透明化
MHA节点包含三个脚本，依赖perl模块；
save_binary_logs:保存和复制当掉的主服务器二进制日志；
apply_diff_relay_logs:识别差异的relay log事件，并应用于其他salve服务器；
purge_relay_logs:清除relay log文件；
需要在所有mysql服务器上安装MHA节点，网站空间，MHA管理服务器也需要安装。MHA管理节点模块内部依赖MHA节点模块；
MHA管理节点通过ssh连接管理mysql服务器和执行MHA节点脚本。MHA节点依赖perl的DBD::mysql模块;
本文环境介绍，香港服务器，操作系统均为rhel5.4
主库：192.168.123.13/dg53.yang.com
备库：192.168.123.14/dg54.yang.com
管理节点：192.168.123.15/dg55.yang.com
在开始之前，请先配置好服务器间的时间同步和名称解析
一:在数据库节点安装mha node
二：管理节点
1：按照步骤一安装mha node
2:安装mha manager
3:编辑配置文件
4:配置manager节点和node节点以及node节点间的ssh公钥信任
5：测试ssh连接
6：测试主从复制情况，默认使用root用户连接
7：启动管理节点进程
三：测试failover过程
1：当前主库为192.168.123.13，关闭主库
2：在管理节点上观察日志输出
[root@dg55 ~]# tail -f /masterha/app1/manager.log
Wed Jun 6 14:50:48 2012 - [info]
192.168.123.13 (current master)
+--192.168.123.14
Wed Jun 6 14:50:48 2012 - [warning] master_ip_failover_script is not defined.
Wed Jun 6 14:50:48 2012 - [warning] shutdown_script is not defined.
Wed Jun 6 14:50:48 2012 - [info] Set master ping interval 1 seconds.
Wed Jun 6 14:50:48 2012 - [warning] secondary_check_script is not defined. It is highly recommended setting it to check master reachability from two or more routes.
Wed Jun 6 14:50:48 2012 - [info] Starting ping health check on 192.168.123.13(192.168.123.13:3306)..
Wed Jun 6 14:50:48 2012 - [info] Ping succeeded, sleeping until it doesn't respond..
Wed Jun 6 14:51:32 2012 - [warning] Got error on MySQL ping: 2006 (MySQL server has gone away)
Wed Jun 6 14:51:32 2012 - [info] HealthCheck: SSH to 192.168.123.13 is reachable.
Wed Jun 6 14:51:33 2012 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)
Wed Jun 6 14:51:33 2012 - [warning] Connection failed 1 time(s)..
Wed Jun 6 14:51:34 2012 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)
Wed Jun 6 14:51:34 2012 - [warning] Connection failed 2 time(s)..
Wed Jun 6 14:51:35 2012 - [warning] Got error on MySQL connect: 2013 (Lost connection to MySQL server at 'reading initial communication packet', system error: 111)
Wed Jun 6 14:51:35 2012 - [warning] Connection failed 3 time(s)..
Wed Jun 6 14:51:35 2012 - [warning] Master is not reachable from health checker!
Wed Jun 6 14:51:35 2012 - [warning] Master 192.168.123.13(192.168.123.13:3306) is not reachable!
Wed Jun 6 14:51:35 2012 - [warning] SSH is reachable.
Wed Jun 6 14:51:35 2012 - [info] Connecting to a master server failed. Reading configuration file /etc/masterha_default.cnf and /etc/masterha/app1.cnf again, and trying to connect to all servers to check server status..
Wed Jun 6 14:51:35 2012 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Wed Jun 6 14:51:35 2012 - [info] Reading application default configurations from /etc/masterha/app1.cnf..
Wed Jun 6 14:51:35 2012 - [info] Reading server configurations from /etc/masterha/app1.cnf..
Wed Jun 6 14:51:35 2012 - [info] Dead Servers:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Alive Servers:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306)
Wed Jun 6 14:51:35 2012 - [info] Alive Slaves:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Wed Jun 6 14:51:35 2012 - [info] Replicating from 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Jun 6 14:51:35 2012 - [info] Checking slave configurations..
Wed Jun 6 14:51:35 2012 - [warning] read_only=1 is not set on slave 192.168.123.14(192.168.123.14:3306).
Wed Jun 6 14:51:35 2012 - [warning] relay_log_purge=0 is not set on slave 192.168.123.14(192.168.123.14:3306).
Wed Jun 6 14:51:35 2012 - [info] Checking replication filtering settings..
Wed Jun 6 14:51:35 2012 - [info] Replication filtering check ok.
Wed Jun 6 14:51:35 2012 - [info] Master is down!
Wed Jun 6 14:51:35 2012 - [info] Terminating monitoring script.
Wed Jun 6 14:51:35 2012 - [info] Got exit code 20 (Master dead).
Wed Jun 6 14:51:35 2012 - [info] MHA::MasterFailover version 0.52.
Wed Jun 6 14:51:35 2012 - [info] Starting master failover.
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] * Phase 1: Configuration Check Phase..
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] Dead Servers:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Checking master reachability via mysql(double check)..
Wed Jun 6 14:51:35 2012 - [info] ok.
Wed Jun 6 14:51:35 2012 - [info] Alive Servers:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306)
Wed Jun 6 14:51:35 2012 - [info] Alive Slaves:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Wed Jun 6 14:51:35 2012 - [info] Replicating from 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Jun 6 14:51:35 2012 - [info] ** Phase 1: Configuration Check Phase completed.
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] * Phase 2: Dead Master Shutdown Phase..
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] Forcing shutdown so that applications never connect to the current master..
Wed Jun 6 14:51:35 2012 - [warning] master_ip_failover_script is not set. Skipping invalidating dead master ip address.
Wed Jun 6 14:51:35 2012 - [warning] shutdown_script is not set. Skipping explicit shutting down of the dead master.
Wed Jun 6 14:51:35 2012 - [info] * Phase 2: Dead Master Shutdown Phase completed.
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] * Phase 3: Master Recovery Phase..
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] * Phase 3.1: Getting Latest Slaves Phase..
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] The latest binary log file/position on all slaves is mysql-bin.000021:107
Wed Jun 6 14:51:35 2012 - [info] Latest slaves (Slaves that received relay log files to the latest):
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Wed Jun 6 14:51:35 2012 - [info] Replicating from 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Jun 6 14:51:35 2012 - [info] The oldest binary log file/position on all slaves is mysql-bin.000021:107
Wed Jun 6 14:51:35 2012 - [info] Oldest slaves:
Wed Jun 6 14:51:35 2012 - [info] 192.168.123.14(192.168.123.14:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Wed Jun 6 14:51:35 2012 - [info] Replicating from 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:35 2012 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] * Phase 3.2: Saving Dead Master's Binlog Phase..
Wed Jun 6 14:51:35 2012 - [info]
Wed Jun 6 14:51:35 2012 - [info] Fetching dead master's binary logs..
Wed Jun 6 14:51:35 2012 - [info] Executing command on the dead master 192.168.123.13(192.168.123.13:3306): save_binary_logs --command=save --start_file=mysql-bin.000021 --start_pos=107 --binlog_dir=/mydata --output_file=/var/tmp/saved_master_binlog_from_192.168.123.13_3306_20120606145135.binlog --handle_raw_binlog=1 --disable_log_bin=0 --manager_version=0.52
Creating /var/tmp if not exists.. ok.
Concat binary/relay logs from mysql-bin.000021 pos 107 to mysql-bin.000021 EOF into /var/tmp/saved_master_binlog_from_192.168.123.13_3306_20120606145135.binlog ..
Dumping binlog format description event, from position 0 to 107.. ok.
Dumping effective binlog data from /mydata/mysql-bin.000021 position 107 to tail(126).. ok.
Concat succeeded.
Wed Jun 6 14:51:36 2012 - [info] scp from root@192.168.123.13:/var/tmp/saved_master_binlog_from_192.168.123.13_3306_20120606145135.binlog to local:/masterha/app1/saved_master_binlog_from_192.168.123.13_3306_20120606145135.binlog succeeded.
Wed Jun 6 14:51:36 2012 - [info] HealthCheck: SSH to 192.168.123.14 is reachable.
Wed Jun 6 14:51:37 2012 - [info]
Wed Jun 6 14:51:37 2012 - [info] * Phase 3.3: Determining New Master Phase..
Wed Jun 6 14:51:37 2012 - [info]
Wed Jun 6 14:51:37 2012 - [info] Finding the latest slave that has all relay logs for recovering other slaves..
Wed Jun 6 14:51:37 2012 - [info] All slaves received relay logs to the same position. No need to resync each other.
Wed Jun 6 14:51:37 2012 - [info] Searching new master from slaves..
Wed Jun 6 14:51:37 2012 - [info] Candidate masters from the configuration file:
Wed Jun 6 14:51:37 2012 - [info] 192.168.123.14(192.168.123.14:3306) Version=5.5.25-log (oldest major version between slaves) log-bin:enabled
Wed Jun 6 14:51:37 2012 - [info] Replicating from 192.168.123.13(192.168.123.13:3306)
Wed Jun 6 14:51:37 2012 - [info] Primary candidate for the new Master (candidate_master is set)
Wed Jun 6 14:51:37 2012 - [info] Non-candidate masters:
Wed Jun 6 14:51:37 2012 - [info] Searching from candidate_master slaves which have received the latest relay log events..
Wed Jun 6 14:51:37 2012 - [info] New master is 192.168.123.14(192.168.123.14:3306)
Wed Jun 6 14:51:37 2012 - [info] Starting master failover..
Wed Jun 6 14:51:37 2012 - [info]
From:
192.168.123.13 (current master)
+--192.168.123.14
