MHA 在线切换是MHA除了自动监控切换换提供的另外一种方式，多用于诸如硬件升级，MySQL数据库迁移等等。该方式提供快速切换和优雅的阻塞写入，无关关闭原有服务器，整个切换过程在0.5-2s 的时间左右，大大减少了停机时间。Online master switch开始只有当所有下列条件得到满足：

 1. IO threads on all slaves are running   // 在所有slave上IO线程运行。

 2. SQL threads on all slaves are running  //SQL线程在所有的slave上正常运行。

 3. Seconds_Behind_Master on all slaves are less or equal than --running_updates_limit seconds  // 在所有的slaves上 Seconds_Behind_Master 要小于等于  running_updates_limit seconds

 4. On master, none of update queries take more than --running_updates_limit seconds in the show processlist output  // 在主上，没有更新查询操作多于running_updates_limit seconds 在show processlist输出结果上。

这些限制的原因是出于安全原因,并尽快切换到新主库。

1.校验当前是否启用masterha_manager（建议停掉）

[root@DBproxy app2]# masterha_check_status --conf=/data/masterha/app1/app1.cnf

app1 (pid:6769) is running(0:PING_OK), master:192.168.0.50

[root@DBproxy app2]#

2.校验slave的IO_threads、SQL_threads、Seconds_Behind_Master

[mysql@MyDB02 masterha]$ mysql -uroot -p123456 -h192.168.0.60 -e 'show slave status \G'|grep -E "Slave_IO_Running|Slave_SQL_Running|Seconds_Behind_Master"

Warning: Using a password on the command line interface can be insecure.

             Slave_IO_Running: Yes

            Slave_SQL_Running: Yes

        Seconds_Behind_Master: 0

      Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it

[mysql@MyDB02 masterha]$

3.实施在线切换

[root@DBproxy masterha]# masterha_master_switch --conf=/data/masterha/app1/app1.cnf --master_state=alive --new_master_host=192.168.0.60 --orig_master_is_new_slave --running_updates_limit=10000 --interactive=0

Sat Jul 16 09:11:00 2016 - [info] MHA::MasterRotate version 0.56.

Sat Jul 16 09:11:00 2016 - [info] Starting online master switch..

Sat Jul 16 09:11:00 2016 - [info]

Sat Jul 16 09:11:00 2016 - [info] * Phase 1: Configuration Check Phase..

Sat Jul 16 09:11:00 2016 - [info]

Sat Jul 16 09:11:00 2016 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.

Sat Jul 16 09:11:00 2016 - [info] Reading application default configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 09:11:00 2016 - [info] Reading server configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 09:11:00 2016 - [info] GTID failover mode = 0

Sat Jul 16 09:11:00 2016 - [info] Current Alive Master: 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 09:11:00 2016 - [info] Alive Slaves:

Sat Jul 16 09:11:00 2016 - [info]   192.168.0.60(192.168.0.60:3306)  Version=5.6.29-log (oldest major version between slaves) log-bin:enabled

Sat Jul 16 09:11:00 2016 - [info]     Replicating from 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 09:11:00 2016 - [info]     Primary candidate for the new Master (candidate_master is set)

Sat Jul 16 09:11:00 2016 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..

Sat Jul 16 09:11:00 2016 - [info]  ok.

Sat Jul 16 09:11:00 2016 - [info] Checking MHA is not monitoring or doing failover..

Sat Jul 16 09:11:00 2016 - [error][/usr/share/perl5/vendor_perl/MHA/MasterRotate.pm, ln142] Getting advisory lock failed on the current master. MHA Monitor runs on the current master. Stop MHA Manager/Monitor and try again.

Sat Jul 16 09:11:00 2016 - [error][/usr/share/perl5/vendor_perl/MHA/ManagerUtil.pm, ln177] Got ERROR:  at /usr/bin/masterha_master_switch line 53

[root@DBproxy masterha]#

将MHA停掉再进行测试

[root@DBproxy masterha]# masterha_stop  --conf=/data/masterha/app1/app1.cnf

Stopped app1 successfully.

[2]-  Exit 1                  nohup masterha_manager --conf=/data/masterha/app1/app1.cnf 2>&1  (wd: /data/masterha/app2)

(wd now: /data/masterha)

[root@DBproxy masterha]#

4.再次实施在线切换

[root@DBproxy masterha]# masterha_master_switch --conf=/data/masterha/app1/app1.cnf --master_state=alive --new_master_host=192.168.0.60 --orig_master_is_new_slave --running_updates_limit=10000 --interactive=0

Sat Jul 16 09:15:03 2016 - [info] MHA::MasterRotate version 0.56.

Sat Jul 16 09:15:03 2016 - [info] Starting online master switch..

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [info] * Phase 1: Configuration Check Phase..

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.

Sat Jul 16 09:15:03 2016 - [info] Reading application default configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 09:15:03 2016 - [info] Reading server configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 09:15:03 2016 - [info] GTID failover mode = 0

Sat Jul 16 09:15:03 2016 - [info] Current Alive Master: 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 09:15:03 2016 - [info] Alive Slaves:

Sat Jul 16 09:15:03 2016 - [info]   192.168.0.60(192.168.0.60:3306)  Version=5.6.29-log (oldest major version between slaves) log-bin:enabled

Sat Jul 16 09:15:03 2016 - [info]     Replicating from 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 09:15:03 2016 - [info]     Primary candidate for the new Master (candidate_master is set)

Sat Jul 16 09:15:03 2016 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..

Sat Jul 16 09:15:03 2016 - [info]  ok.

Sat Jul 16 09:15:03 2016 - [info] Checking MHA is not monitoring or doing failover..

Sat Jul 16 09:15:03 2016 - [info] Checking replication health on 192.168.0.60..

Sat Jul 16 09:15:03 2016 - [info]  ok.

Sat Jul 16 09:15:03 2016 - [info] 192.168.0.60 can be new master.

Sat Jul 16 09:15:03 2016 - [info]

From:

192.168.0.50(192.168.0.50:3306) (current master)

 +--192.168.0.60(192.168.0.60:3306)

To:

192.168.0.60(192.168.0.60:3306) (new master)

 +--192.168.0.50(192.168.0.50:3306)

Sat Jul 16 09:15:03 2016 - [info] Checking whether 192.168.0.60(192.168.0.60:3306) is ok for the new master..

Sat Jul 16 09:15:03 2016 - [info]  ok.

Sat Jul 16 09:15:03 2016 - [info] 192.168.0.50(192.168.0.50:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host.

Sat Jul 16 09:15:03 2016 - [info] 192.168.0.50(192.168.0.50:3306): Resetting slave pointing to the dummy host.

Sat Jul 16 09:15:03 2016 - [info] ** Phase 1: Configuration Check Phase completed.

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [info] * Phase 2: Rejecting updates Phase..

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [warning] master_ip_online_change_script is not defined. Skipping disabling writes on the current master.

Sat Jul 16 09:15:03 2016 - [info] Locking all tables on the orig master to reject updates from everybody (including root):

Sat Jul 16 09:15:03 2016 - [info] Executing FLUSH TABLES WITH READ LOCK..

Sat Jul 16 09:15:03 2016 - [info]  ok.

Sat Jul 16 09:15:03 2016 - [info] Orig master binlog:pos is mysql-bin.000009:40355591.

Sat Jul 16 09:15:03 2016 - [info]  Waiting to execute all relay logs on 192.168.0.60(192.168.0.60:3306)..

Sat Jul 16 09:15:03 2016 - [info]  master_pos_wait(mysql-bin.000009:40355591) completed on 192.168.0.60(192.168.0.60:3306). Executed 0 events.

Sat Jul 16 09:15:03 2016 - [info]   done.

Sat Jul 16 09:15:03 2016 - [info] Getting new master's binlog name and position..

Sat Jul 16 09:15:03 2016 - [info]  mysql-bin.000006:120

Sat Jul 16 09:15:03 2016 - [info]  All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.0.60', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000006', MASTER_LOG_POS=120, MASTER_USER='repl', MASTER_PASSWORD='xxx';

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [info] * Switching slaves in parallel..

Sat Jul 16 09:15:03 2016 - [info]

Sat Jul 16 09:15:03 2016 - [info] Unlocking all tables on the orig master:

Sat Jul 16 09:15:03 2016 - [info] Executing UNLOCK TABLES..

Sat Jul 16 09:15:03 2016 - [info]  ok.

Sat Jul 16 09:15:03 2016 - [info] Starting orig master as a new slave..

Sat Jul 16 09:15:03 2016 - [info]  Resetting slave 192.168.0.50(192.168.0.50:3306) and starting replication from the new master 192.168.0.60(192.168.0.60:3306)..

Sat Jul 16 09:15:03 2016 - [info]  Executed CHANGE MASTER.

Sat Jul 16 09:15:14 2016 - [error][/usr/share/perl5/vendor_perl/MHA/Server.pm, ln784] Slave could not be started on 192.168.0.50(192.168.0.50:3306)! Check slave status.

Sat Jul 16 09:15:14 2016 - [error][/usr/share/perl5/vendor_perl/MHA/Server.pm, ln862] Starting slave IO/SQL thread on 192.168.0.50(192.168.0.50:3306) failed!

Sat Jul 16 09:15:14 2016 - [error][/usr/share/perl5/vendor_perl/MHA/MasterRotate.pm, ln573]  Failed!

Sat Jul 16 09:15:14 2016 - [error][/usr/share/perl5/vendor_perl/MHA/MasterRotate.pm, ln602] Switching master to 192.168.0.60(192.168.0.60:3306) done, but switching slaves partially failed.

[root@DBproxy masterha]#

通过主从机本身的日志判断 可能是主从机中ip和主机名的未做映射导致的。修改hosts

主机的/etc/hosts

127.0.0.1 MyDB01

从机的/etc/hosts

127.0.0.1 MyDB02

修改后主从机器的/etc/hosts

[root@MyDB02 ~]# more /etc/hosts

192.168.0.60  MyDB02

192.168.0.50  MyDB01

因之前的操作为完全成功，导致两台机器为双主架构。手动切换后调整为最初架构一主一从。在线切换前做一次检查：

[root@DBproxy app1]# masterha_check_repl --conf=/data/masterha/app1/app1.cnf

Sat Jul 16 10:24:49 2016 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.

Sat Jul 16 10:24:49 2016 - [info] Reading application default configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 10:24:49 2016 - [info] Reading server configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 10:24:49 2016 - [info] MHA::MasterMonitor version 0.56.

Sat Jul 16 10:24:49 2016 - [info] GTID failover mode = 0

Sat Jul 16 10:24:49 2016 - [info] Dead Servers:

Sat Jul 16 10:24:49 2016 - [info] Alive Servers:

Sat Jul 16 10:24:49 2016 - [info]   192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:24:49 2016 - [info]   192.168.0.60(192.168.0.60:3306)

Sat Jul 16 10:24:49 2016 - [info] Alive Slaves:

Sat Jul 16 10:24:49 2016 - [info]   192.168.0.60(192.168.0.60:3306)  Version=5.6.29-log (oldest major version between slaves) log-bin:enabled

Sat Jul 16 10:24:49 2016 - [info]     Replicating from 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:24:49 2016 - [info]     Primary candidate for the new Master (candidate_master is set)

Sat Jul 16 10:24:49 2016 - [info] Current Alive Master: 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:24:49 2016 - [info] Checking slave configurations..

Sat Jul 16 10:24:49 2016 - [info]  read_only=1 is not set on slave 192.168.0.60(192.168.0.60:3306).

Sat Jul 16 10:24:49 2016 - [info] Checking replication filtering settings..

Sat Jul 16 10:24:49 2016 - [info]  binlog_do_db= , binlog_ignore_db=

Sat Jul 16 10:24:49 2016 - [info]  Replication filtering check ok.

Sat Jul 16 10:24:49 2016 - [info] GTID (with auto-pos) is not supported

Sat Jul 16 10:24:49 2016 - [info] Starting SSH connection tests..

Sat Jul 16 10:24:50 2016 - [info] All SSH connection tests passed successfully.

Sat Jul 16 10:24:50 2016 - [info] Checking MHA Node version..

Sat Jul 16 10:24:51 2016 - [info]  Version check ok.

Sat Jul 16 10:24:51 2016 - [info] Checking SSH publickey authentication settings on the current master..

Sat Jul 16 10:24:51 2016 - [info] HealthCheck: SSH to 192.168.0.50 is reachable.

Sat Jul 16 10:24:51 2016 - [info] Master MHA Node version is 0.56.

Sat Jul 16 10:24:51 2016 - [info] Checking recovery script configurations on 192.168.0.50(192.168.0.50:3306)..

Sat Jul 16 10:24:51 2016 - [info]   Executing command: save_binary_logs --command=test --start_pos=4 --binlog_dir=/data/mysql/3306/binlog --output_file=/data/masterha/app1/save_binary_logs_test --manager_version=0.56 --start_file=mysql-bin.000010

Sat Jul 16 10:24:51 2016 - [info]   Connecting to root@192.168.0.50(192.168.0.50:22)..

  Creating /data/masterha/app1 if not exists..    ok.

  Checking output directory is accessible or not..

   ok.

  Binlog found at /data/mysql/3306/binlog, up to mysql-bin.000010

Sat Jul 16 10:24:52 2016 - [info] Binlog setting check done.

Sat Jul 16 10:24:52 2016 - [info] Checking SSH publickey authentication and checking recovery script configurations on all alive slave servers..

Sat Jul 16 10:24:52 2016 - [info]   Executing command : apply_diff_relay_logs --command=test --slave_user='root' --slave_host=192.168.0.60 --slave_ip=192.168.0.60 --slave_port=3306 --workdir=/data/masterha/app1 --target_version=5.6.29-log --manager_version=0.56 --relay_log_info=/data/mysql/3306/data/relay-log.info  --relay_dir=/data/mysql/3306/data/  --slave_pass=xxx

Sat Jul 16 10:24:52 2016 - [info]   Connecting to root@192.168.0.60(192.168.0.60:22)..

  Checking slave recovery environment settings..

    Opening /data/mysql/3306/data/relay-log.info ... ok.

    Relay log found at /data/mysql/3306/binlog, up to relay-bin.000002

    Temporary relay log file is /data/mysql/3306/binlog/relay-bin.000002

    Testing mysql connection and privileges.. done.

    Testing mysqlbinlog output.. done.

    Cleaning up test file(s).. done.

Sat Jul 16 10:24:53 2016 - [info] Slaves settings check done.

Sat Jul 16 10:24:53 2016 - [info]

192.168.0.50(192.168.0.50:3306) (current master)

 +--192.168.0.60(192.168.0.60:3306)

Sat Jul 16 10:24:53 2016 - [info] Checking replication health on 192.168.0.60..

Sat Jul 16 10:24:53 2016 - [info]  ok.

Sat Jul 16 10:24:53 2016 - [warning] master_ip_failover_script is not defined.

Sat Jul 16 10:24:53 2016 - [warning] shutdown_script is not defined.

Sat Jul 16 10:24:53 2016 - [info] Got exit code 0 (Not master dead).

MySQL Replication Health is OK.

5.实施切换

[root@DBproxy app1]# masterha_master_switch --conf=/data/masterha/app1/app1.cnf --master_state=alive --new_master_host=192.168.0.60 --orig_master_is_new_slave --running_updates_limit=10000 --interactive=0

Sat Jul 16 10:26:59 2016 - [info] MHA::MasterRotate version 0.56.

Sat Jul 16 10:26:59 2016 - [info] Starting online master switch..

Sat Jul 16 10:26:59 2016 - [info]

Sat Jul 16 10:26:59 2016 - [info] * Phase 1: Configuration Check Phase..

Sat Jul 16 10:26:59 2016 - [info]

Sat Jul 16 10:26:59 2016 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.

Sat Jul 16 10:26:59 2016 - [info] Reading application default configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 10:26:59 2016 - [info] Reading server configuration from /data/masterha/app1/app1.cnf..

Sat Jul 16 10:26:59 2016 - [info] GTID failover mode = 0

Sat Jul 16 10:26:59 2016 - [info] Current Alive Master: 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:26:59 2016 - [info] Alive Slaves:

Sat Jul 16 10:26:59 2016 - [info]   192.168.0.60(192.168.0.60:3306)  Version=5.6.29-log (oldest major version between slaves) log-bin:enabled

Sat Jul 16 10:26:59 2016 - [info]     Replicating from 192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:26:59 2016 - [info]     Primary candidate for the new Master (candidate_master is set)

Sat Jul 16 10:26:59 2016 - [info] Executing FLUSH NO_WRITE_TO_BINLOG TABLES. This may take long time..

Sat Jul 16 10:26:59 2016 - [info]  ok.

Sat Jul 16 10:26:59 2016 - [info] Checking MHA is not monitoring or doing failover..

Sat Jul 16 10:26:59 2016 - [info] Checking replication health on 192.168.0.60..

Sat Jul 16 10:26:59 2016 - [info]  ok.

Sat Jul 16 10:26:59 2016 - [info] 192.168.0.60 can be new master.

Sat Jul 16 10:26:59 2016 - [info]

From:

192.168.0.50(192.168.0.50:3306) (current master)

 +--192.168.0.60(192.168.0.60:3306)

To:

192.168.0.60(192.168.0.60:3306) (new master)

 +--192.168.0.50(192.168.0.50:3306)

Sat Jul 16 10:26:59 2016 - [info] Checking whether 192.168.0.60(192.168.0.60:3306) is ok for the new master..

Sat Jul 16 10:26:59 2016 - [info]  ok.

Sat Jul 16 10:26:59 2016 - [info] 192.168.0.50(192.168.0.50:3306): SHOW SLAVE STATUS returned empty result. To check replication filtering rules, temporarily executing CHANGE MASTER to a dummy host.

Sat Jul 16 10:26:59 2016 - [info] 192.168.0.50(192.168.0.50:3306): Resetting slave pointing to the dummy host.

Sat Jul 16 10:26:59 2016 - [info] ** Phase 1: Configuration Check Phase completed.

Sat Jul 16 10:26:59 2016 - [info]

Sat Jul 16 10:26:59 2016 - [info] * Phase 2: Rejecting updates Phase..

Sat Jul 16 10:26:59 2016 - [info]

Sat Jul 16 10:26:59 2016 - [warning] master_ip_online_change_script is not defined. Skipping disabling writes on the current master.

Sat Jul 16 10:26:59 2016 - [info] Locking all tables on the orig master to reject updates from everybody (including root):

Sat Jul 16 10:26:59 2016 - [info] Executing FLUSH TABLES WITH READ LOCK..

Sat Jul 16 10:26:59 2016 - [info]  ok.

Sat Jul 16 10:26:59 2016 - [info] Orig master binlog:pos is mysql-bin.000010:120.

Sat Jul 16 10:26:59 2016 - [info]  Waiting to execute all relay logs on 192.168.0.60(192.168.0.60:3306)..

Sat Jul 16 10:27:00 2016 - [info]  master_pos_wait(mysql-bin.000010:120) completed on 192.168.0.60(192.168.0.60:3306). Executed 0 events.

Sat Jul 16 10:27:00 2016 - [info]   done.

Sat Jul 16 10:27:00 2016 - [info] Getting new master's binlog name and position..

Sat Jul 16 10:27:00 2016 - [info]  mysql-bin.000008:239

Sat Jul 16 10:27:00 2016 - [info]  All other slaves should start replication from here. Statement should be: CHANGE MASTER TO MASTER_HOST='192.168.0.60', MASTER_PORT=3306, MASTER_LOG_FILE='mysql-bin.000008', MASTER_LOG_POS=239, MASTER_USER='repl', MASTER_PASSWORD='xxx';

Sat Jul 16 10:27:00 2016 - [info]

Sat Jul 16 10:27:00 2016 - [info] * Switching slaves in parallel..

Sat Jul 16 10:27:00 2016 - [info]

Sat Jul 16 10:27:00 2016 - [info] Unlocking all tables on the orig master:

Sat Jul 16 10:27:00 2016 - [info] Executing UNLOCK TABLES..

Sat Jul 16 10:27:00 2016 - [info]  ok.

Sat Jul 16 10:27:00 2016 - [info] Starting orig master as a new slave..

Sat Jul 16 10:27:00 2016 - [info]  Resetting slave 192.168.0.50(192.168.0.50:3306) and starting replication from the new master 192.168.0.60(192.168.0.60:3306)..

Sat Jul 16 10:27:00 2016 - [info]  Executed CHANGE MASTER.

Sat Jul 16 10:27:00 2016 - [info]  Slave started.

Sat Jul 16 10:27:00 2016 - [info] All new slave servers switched successfully.

Sat Jul 16 10:27:00 2016 - [info]

Sat Jul 16 10:27:00 2016 - [info] * Phase 5: New master cleanup phase..

Sat Jul 16 10:27:00 2016 - [info]

Sat Jul 16 10:27:00 2016 - [info]  192.168.0.60: Resetting slave info succeeded.

Sat Jul 16 10:27:00 2016 - [info] Switching master to 192.168.0.60(192.168.0.60:3306) completed successfully.

[root@DBproxy app1]#

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