一：MHA介绍
什么是mha，有什么特性 ？
- 主服务器的自动监控和故障转移
MHA监控复制架构的主服务器，一旦检测到主服务器故障，就会自动进行故障转移。即使有些从服务器没有收到最新的relay log，MHA自动从最新的从服务器上识别差异的relay log并把这些日志应用到其他从服务器上，因此所有的从服务器保持一致性了。MHA通常在几秒内完成故障转移，9-12秒可以检测出主服务器故障，7-10秒内关闭故障的主服务器以避免脑裂，几秒中内应用差异的relay log到新的主服务器上，整个过程可以在10-30s内完成。还可以设置优先级指定其中的一台slave作为master的候选人。由于MHA在slaves之间修复一致性，因此可以将任何slave变成新的master，而不会发生一致性的问题，从而导致复制失败。
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。
目前MHA主要支持一主多从的架构，要搭建MHA,要求一个复制集群中必须最少有三台数据库服务器，一主二从，即一台充当master，一台充当备用master，另外一台充当从库，因为至少需要三台服务器，出于机器成本的考虑，淘宝也在该基础上进行了改造，目前淘宝TMHA已经支持一主一从。
- 交互式主服务器故障转移
可以只使用MHA的故障转移，而不用于监控主服务器，当主服务器故障时，人工调用MHA来进行故障故障。
- 非交互式的主故障转移
不监控主服务器，但自动实现故障转移。这种特征适用于已经使用其他软件来监控主服务器状态，比如heartbeat来检测主服务器故障和虚拟IP地址接管，可以使用MHA来实现故障转移和slave服务器晋级为master服务器。
- 在线切换主从服务器
在许多情况下，需要将现有的主服务器迁移到另外一台服务器上。比如主服务器硬件故障，RAID控制卡需要重建，将主服务器移到性能更好的服务器上等等。维护主服务器引起性能下降，导致停机时间至少无法写入数据。另外，阻塞或杀掉当前运行的会话会导致主主之间数据不一致的问题发生。MHA提供快速切换和优雅的阻塞写入，这个切换过程只需要0.5-2s的时间，这段时间内数据是无法写入的。在很多情况下，0.5-2s的阻塞写入是可以接受的。因此切换主服务器不需要计划分配维护时间窗口。
- MHA由两部分组成：MHA Manager（管理节点）和MHA Node（数据节点）
管理节点可以和数据节点在同一台机器，也可以不在同一台机器上。
- MHA比较灵活，可以写脚本，来进行故障转移，或者主从切换等。
- mha出现故障后，配置文件会被修改掉.
缺点：
1、 虽然MHA试图从宕机的主服务器上保存二进制日志，但也会有问题。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最新数据。
2、 当主DB故障，切换到另外的服务器上后，即使恢复了原来的主DB，也不能立即加入整套MHA系统中，得重新部署。而且当发生一次切换后，管理节点的监控进程就会自动退出，需要用脚本来自动启动。
二、实验环境
准备：
- 3台服务器，1台既做管理机，又做数据机
- 另外两台做为数据机
已经搭建好主从配置，共3台服务器（最好是4台，见总结）
192.168.160.153 master （管理manager）
192.168.160.154 slave1
192.168.160.155 slave2大致步骤：
A.首先用ssh-keygen实现四台主机之间相互免密钥登录
B.安装MHAmha4mysql-node，mha4mysql-manager 软件包
C.建立master，slave1，slave2之间主从复制
D.管理机manager上配置MHA文件
E.masterha_check_ssh工具验证ssh信任登录是否成功
F.masterha_check_repl工具验证mysql复制是否成功
G.启动MHA manager,并监控日志文件
H.测试master(156)宕机后，是否会自动切换三、具体搭建MHA
1：修改/etc/hosts
在3台机器上都添加每台服务器的主机名,如：
192.168.160.153 master （管理节点，数据节点）
192.168.160.154 slave1 （数据节点）
192.168.160.155 slave2 （数据节点）2. 配置主机信任关系
#在192.168.160.153生成密码文件，然后将其拷贝到本机，192.168.160.151和192.168.160.152上。
[root@localhost ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
2e:20:f3:cd:2a:81:c5:b9:b6:7c:c3:32:5b:8c:a1:26 root@localhost.localdomain
The key's randomart image is:
+--[ RSA 2048]----+
| |
| |
| . . |
| + |
| o+.. S |
|..+B + . |
|E+.++ + . |
|o *.+. . |
| .*.. |
+-----------------+
依次拷贝到150，151，152 三台服务器上
# ssh-copy-id root@192.168.160.154
....
# ssh-copy-id root@192.168.160.155
[root@localhost ~]# ssh-copy-id root@192.168.160.153
The authenticity of host '192.168.160.152 (192.168.160.152)' can't be established.
RSA key fingerprint is 4c:c2:d9:5a:fd:5b:ec:c2:b0:51:89:74:79:c0:8d:77.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.160.152' (RSA) to the list of known hosts.
root@192.168.160.152's password:
Now try logging into the machine, with "ssh 'root@192.168.160.152'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.重复上面的步骤，依次在151和152上也生成密码文件，然后拷贝到本机与其他机器上
配置完成后，用ssh ip测试，看是否能免密码登陆，各个机子之间依次测试能否免密登录。
[root@localhost ~]# ssh 192.168.160.153
Last login: Wed Jul 25 14:22:12 2018 from 192.168.160.1
#上述说明已经登录成功3. 安装MHA
1.下载MHA rpm源在个人github上
#数据节点需要的rpm包
wget https://github.com/demored/data/raw/master/mha4mysql-node-0.56-0.el6.noarch.rpm
#管理节点需要的rpm包
wget https://github.com/demored/data/raw/master/mha4mysql-manager-0.56-0.el6.noarch.rpm2. 在所有数据节点上安装：
本次实验的数据节点为：154和155，153即为数据节点也为管理节点
yum install perl-DBD-MySQL -y
rpm -ivh mha4mysql-node-0.56-0.el6.noarch.rpm #数据节点包安装安装完成后会在/usr/bin目录下生成以下脚本文件(这些工具通常由MHA Manager的脚本触发，无需人为操作)：
save_binary_logs //保存和复制master的二进制日志
apply_diff_relay_logs //识别差异的中继日志事件并将其差异的事件应用于其他的slave
filter_mysqlbinlog //去除不必要的ROLLBACK事件（MHA已不再使用这个工具）
purge_relay_logs //清除中继日志（不会阻塞SQL线程）3. 在管理节点上安装：
本次实验的管理节点为153
yum install perl-DBD-MySQL -y
yum install perl-Config-Tiny -y
yum install epel-release -y
yum install perl-Log-Dispatch -y
yum install perl-Parallel-ForkManager -y
yum install perl-Time-HiRes
# 必须要安装这个插件，否则会报
perl(Time::HiRes) is needed by mha4mysql-manager-0.56-0.el6.noarch
rpm -ivh mha4mysql-manager-0.56-0.el6.noarch.rpm安装完成后会在/usr/bin目录下生成以下脚本文件:
-rwxr-xr-x. 1 root root 1995 Apr 1 2014 masterha_check_repl
-rwxr-xr-x. 1 root root 1779 Apr 1 2014 masterha_check_ssh
-rwxr-xr-x. 1 root root 1865 Apr 1 2014 masterha_check_status
-rwxr-xr-x. 1 root root 3201 Apr 1 2014 masterha_conf_host
-rwxr-xr-x. 1 root root 2517 Apr 1 2014 masterha_manager
-rwxr-xr-x. 1 root root 2165 Apr 1 2014 masterha_master_monitor
-rwxr-xr-x. 1 root root 2373 Apr 1 2014 masterha_master_switch
-rwxr-xr-x. 1 root root 5171 Apr 1 2014 masterha_secondary_check
-rwxr-xr-x. 1 root root 1739 Apr 1 2014 masterha_stop
-rwxr-xr-x. 1 root root 4807 Apr 1 2014 filter_mysqlbinlog
-rwxr-xr-x. 1 root root 7525 Apr 1 2014 save_binary_logs
-rwxr-xr-x. 1 root root 8261 Apr 1 2014 purge_relay_logs
-rwxr-xr-x. 1 root root 16367 Apr 1 2014 apply_diff_relay_logs配置主从复制
master : 153
slave1 : 154
slave2 : 155
步骤：略
4. 从服务器配置
从服务器，要加上relay_log_purge=0，不加的话，会报出warning,relay_log_purge=0 is not set on slave
4.1 在线设置
set global relay_log_purge = 0;4.2 修改配置文件
vi /etc/my.cnf
添加：
relay_log_purge = 05. 配置mha manage
5.1 添加管理账号
在数据节点上执行以下操作
grant all privileges on *.* TO mha@'192.168.160.%' IDENTIFIED BY 'test';
flush privileges;5.2：配置/etc/mha/app1.cnf
#只在管理端做，manage这台机器
mkdir /etc/mha
mkdir -p /var/log/mha/app1
vim /etc/mha/app1.cnf
添加：
[server default]
manager_log=/var/log/mha/app1/manager.log
manager_workdir=/var/log/mha/ #目录可以任意指定
master_binlog_dir=/data/mysql/data #mysql数据库目录,这个也可以单独配置在下面的server中
user=mha ##mysql管理用戶名
password=test
ping_interval=2 #ping间隔时间，用来检测master是否正常
repl_password=123456
repl_user=repl #mysql复制帐号，用来在主从机之间同步二进制日志等
ssh_user=root #ssh免密钥登录的帐号名
[server1]
hostname=192.168.160.153
port=3306
[server2]
candidate_master=1 #master机宕掉后,优先启用这台作为新master，前台必须要给这台授权，grant replcation ...
check_repl_delay=0
hostname=192.168.160.154
port=3306
[server3]
hostname=192.168.160.155
port=3306
no_master =1 #设置no_master=1使主机不能成为新master在server default中的配置，是三台机器共同的配置，也可以放到具体的server中进行定制
6 检查mha manage是不是配置成功
6.1 检查ssh登录
[root@ser6-51 .ssh]# masterha_check_ssh --conf=/etc/mha/app1.cnf
Fri Aug 7 15:11:07 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Fri Aug 7 15:11:07 2015 - [info] Reading application default configuration from /etc/mha/app1.cnf..
Fri Aug 7 15:11:07 2015 - [info] Reading server configuration from /etc/mha/app1.cnf..
Fri Aug 7 15:11:07 2015 - [info] Starting SSH connection tests..
Fri Aug 7 15:11:08 2015 - [debug]
Fri Aug 7 15:11:07 2015 - [debug] Connecting via SSH from root@192.168.6.51(192.168.6.51:22) to root@192.168.6.52(192.168.6.52:22)..
Fri Aug 7 15:11:07 2015 - [debug] ok.
Fri Aug 7 15:11:07 2015 - [debug] Connecting via SSH from root@192.168.6.51(192.168.6.51:22) to root@192.168.6.70(192.168.6.70:22)..
Fri Aug 7 15:11:08 2015 - [debug] ok.
Fri Aug 7 15:11:08 2015 - [debug]
Fri Aug 7 15:11:07 2015 - [debug] Connecting via SSH from root@192.168.6.52(192.168.6.52:22) to root@192.168.6.51(192.168.6.51:22)..
Fri Aug 7 15:11:08 2015 - [debug] ok.
Fri Aug 7 15:11:08 2015 - [debug] Connecting via SSH from root@192.168.6.52(192.168.6.52:22) to root@192.168.6.70(192.168.6.70:22)..
Fri Aug 7 15:11:08 2015 - [debug] ok.
Fri Aug 7 15:11:09 2015 - [debug]
Fri Aug 7 15:11:08 2015 - [debug] Connecting via SSH from root@192.168.6.70(192.168.6.70:22) to root@192.168.6.51(192.168.6.51:22)..
Fri Aug 7 15:11:08 2015 - [debug] ok.
Fri Aug 7 15:11:09 2015 - [debug] Connecting via SSH from root@192.168.6.70(192.168.6.70:22) to root@192.168.6.52(192.168.6.52:22)..
Fri Aug 7 15:11:09 2015 - [debug] ok.
Fri Aug 7 15:11:09 2015 - [info] All SSH connection tests passed successfully.备注：
如果看到，All SSH connection tests passed successfully，就说明ssh配置成功了
假如报错：
[error][/usr/share/perl5/vendor_perl/MHA/SSHCheck.pm, ln63]
将.ssh下的内容全部清空，然后重新认证即可
6.2 检查mysql replication是否配置成功
[root@ser6-51 .ssh]# masterha_check_repl --conf=/etc/mha/app1.cnf
Fri Aug 7 15:33:11 2015 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.
Fri Aug 7 15:33:11 2015 - [info] Reading application default configuration from /etc/mha/app1.cnf..
Fri Aug 7 15:33:11 2015 - [info] Reading server configuration from /etc/mha/app1.cnf..
Fri Aug 7 15:33:11 2015 - [info] MHA::MasterMonitor version 0.56.
Fri Aug 7 15:33:11 2015 - [info] GTID failover mode = 0
Fri Aug 7 15:33:11 2015 - [info] Dead Servers:
Fri Aug 7 15:33:11 2015 - [info] Alive Servers:
Fri Aug 7 15:33:11 2015 - [info] 192.168.6.51(192.168.6.51:3306)
Fri Aug 7 15:33:11 2015 - [info] 192.168.6.52(192.168.6.52:3306)
Fri Aug 7 15:33:11 2015 - [info] 192.168.6.70(192.168.6.70:3306)
Fri Aug 7 15:33:11 2015 - [info] Alive Slaves:
Fri Aug 7 15:33:11 2015 - [info] 192.168.6.52(192.168.6.52:3306) Version=5.6.20-r5436-log (oldest major version between slaves) log-bin:enabled
Fri Aug 7 15:33:11 2015 - [info] Replicating from 192.168.6.51(192.168.6.51:3306)
Fri Aug 7 15:33:11 2015 - [info] Primary candidate for the new Master (candidate_master is set)
Fri Aug 7 15:33:11 2015 - [info] 192.168.6.70(192.168.6.70:3306) Version=5.6.20-r5436-log (oldest major version between slaves) log-bin:enabled
Fri Aug 7 15:33:11 2015 - [info] Replicating from 192.168.6.51(192.168.6.51:3306)
Fri Aug 7 15:33:11 2015 - [info] Current Alive Master: 192.168.6.51(192.168.6.51:3306)
Fri Aug 7 15:33:11 2015 - [info] Checking slave configurations..
Fri Aug 7 15:33:11 2015 - [info] Checking replication filtering settings..
Fri Aug 7 15:33:11 2015 - [info] binlog_do_db= , binlog_ignore_db=
Fri Aug 7 15:33:11 2015 - [info] Replication filtering check ok.
Fri Aug 7 15:33:11 2015 - [info] GTID (with auto-pos) is not supported
Fri Aug 7 15:33:11 2015 - [info] Starting SSH connection tests..
Fri Aug 7 15:33:13 2015 - [info] All SSH connection tests passed successfully.
Fri Aug 7 15:33:13 2015 - [info] Checking MHA Node version..
Fri Aug 7 15:33:14 2015 - [info] Version check ok.
Fri Aug 7 15:33:14 2015 - [info] Checking SSH publickey authentication settings on the current master..
Fri Aug 7 15:33:14 2015 - [info] HealthCheck: SSH to 192.168.6.51 is reachable.
Fri Aug 7 15:33:14 2015 - [info] Master MHA Node version is 0.56.
Fri Aug 7 15:33:14 2015 - [info] Checking recovery script configurations on 192.168.6.51(192.168.6.51:3306)..
Fri Aug 7 15:33:14 2015 - [info] Executing command: save_binary_logs --command=test --start_pos=4 --binlog_dir=/data/mysql/data --output_file=/var/tmp/save_binary_logs_test --manager_version=0.56 --start_file=mysql-bin.000032
Fri Aug 7 15:33:14 2015 - [info] Connecting to root@192.168.6.51(192.168.6.51:22)..
Creating /var/tmp if not exists.. ok.
Checking output directory is accessible or not..
ok.
Binlog found at /data/mysql/data, up to mysql-bin.000032
Fri Aug 7 15:33:15 2015 - [info] Binlog setting check done.
Fri Aug 7 15:33:15 2015 - [info] Checking SSH publickey authentication and checking recovery script configurations on all alive slave servers..
Fri Aug 7 15:33:15 2015 - [info] Executing command : apply_diff_relay_logs --command=test --slave_user='mha' --slave_host=192.168.6.52 --slave_ip=192.168.6.52 --slave_port=3306 --workdir=/var/tmp --target_version=5.6.20-r5436-log --manager_version=0.56 --relay_log_info=/data/mysql/data/relay-log.info --relay_dir=/data/mysql/data/ --slave_pass=xxx
Fri Aug 7 15:33:15 2015 - [info] Connecting to root@192.168.6.52(192.168.6.52:22)..
Checking slave recovery environment settings..
Opening /data/mysql/data/relay-log.info ... ok.
Relay log found at /data/mysql/data, up to mysql-relay-bin.000002
Temporary relay log file is /data/mysql/data/mysql-relay-bin.000002
Testing mysql connection and privileges..Warning: Using a password on the command line interface can be insecure.
done.
Testing mysqlbinlog output.. done.
Cleaning up test file(s).. done.
Fri Aug 7 15:33:16 2015 - [info] Executing command : apply_diff_relay_logs --command=test --slave_user='mha' --slave_host=192.168.6.70 --slave_ip=192.168.6.70 --slave_port=3306 --workdir=/var/tmp --target_version=5.6.20-r5436-log --manager_version=0.56 --relay_log_info=/data/mysql/data/relay-log.info --relay_dir=/data/mysql/data/ --slave_pass=xxx
Fri Aug 7 15:33:16 2015 - [info] Connecting to root@192.168.6.70(192.168.6.70:22)..
Checking slave recovery environment settings..
Opening /data/mysql/data/relay-log.info ... ok.
Relay log found at /data/mysql/data, up to mysql-relay-bin.000003
Temporary relay log file is /data/mysql/data/mysql-relay-bin.000003
Testing mysql connection and privileges..Warning: Using a password on the command line interface can be insecure.
done.
Testing mysqlbinlog output.. done.
Cleaning up test file(s).. done.
Fri Aug 7 15:33:17 2015 - [info] Slaves settings check done.
Fri Aug 7 15:33:17 2015 - [info]
192.168.6.51(192.168.6.51:3306) (current master)
+--192.168.6.52(192.168.6.52:3306)
+--192.168.6.70(192.168.6.70:3306)
Fri Aug 7 15:33:17 2015 - [info] Checking replication health on 192.168.6.52..
Fri Aug 7 15:33:17 2015 - [info] ok.
Fri Aug 7 15:33:17 2015 - [info] Checking replication health on 192.168.6.70..
Fri Aug 7 15:33:17 2015 - [info] ok.
Fri Aug 7 15:33:17 2015 - [warning] master_ip_failover_script is not defined.
Fri Aug 7 15:33:17 2015 - [warning] shutdown_script is not defined.
Fri Aug 7 15:33:17 2015 - [info] Got exit code 0 (Not master dead).
MySQL Replication Health is OK.报错1：
Fri Aug 7 15:17:21 2015 - [info] Connecting to root@192.168.6.52(192.168.6.52:22)..
Can't exec "mysqlbinlog": No such file or directory at /usr/share/perl5/vendor_perl/MHA/BinlogManager.pm line 106.
mysqlbinlog version command failed with rc 1:0, please verify PATH, LD_LIBRARY_PATH, and client options
at /usr/bin/apply_diff_relay_logs line 493
Fri Aug 7 15:17:21 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln205] Slaves settings check failed!
Fri Aug 7 15:17:21 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln413] Slave configuration failed.
Fri Aug 7 15:17:21 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln424] Error happened on checking configurations. at /usr/bin/masterha_check_repl line 48
Fri Aug 7 15:17:21 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln523] Error happened on monitoring servers.
Fri Aug 7 15:17:21 2015 - [info] Got exit code 1 (Not master dead).
MySQL Replication Health is NOT OK!在所有数据节点上都创建一下软连接：
ln -s /usr/local/mysql/bin/mysqlbinlog /usr/bin/mysqlbinlog再次运行：
masterha_check_repl --conf=/etc/mha/app1.cnf错误2：
Testing mysql connection and privileges..sh: mysql: command not found
mysql command failed with rc 127:0!
at /usr/bin/apply_diff_relay_logs line 375
main::check() called at /usr/bin/apply_diff_relay_logs line 497
eval {...} called at /usr/bin/apply_diff_relay_logs line 475
main::main() called at /usr/bin/apply_diff_relay_logs line 120
Fri Aug 7 15:28:08 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln205] Slaves settings check failed!
Fri Aug 7 15:28:08 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln413] Slave configuration failed.
Fri Aug 7 15:28:08 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln424] Error happened on checking configurations. at /usr/bin/masterha_check_repl line 48
Fri Aug 7 15:28:08 2015 - [error][/usr/share/perl5/vendor_perl/MHA/MasterMonitor.pm, ln523] Error happened on monitoring servers.
Fri Aug 7 15:28:08 2015 - [info] Got exit code 1 (Not master dead).在所有数据节点上建立软连接：
ln -s /usr/local/mysql/bin/mysql /usr/bin/mysql7. 在管理端启动监控
root@ser6-51 .ssh]# nohup masterha_manager --conf=/etc/mha/app1.cnf --remove_dead_master_conf --ignore_last_failover < /dev/null > /var/log/mha/app1/manager.log 2>&1 &
[1] 14694
[root@ser6-51 .ssh]# masterha_check_status --conf=/etc/mha/app1.cnf //查看状态
app1 (pid:14694) is running(0:PING_OK), master:192.168.6.51
# masterha_stop --conf=/etc/mha/app1.cnf //关闭监控8：测试
在53上关闭Mysql实例：
[root@ser6-51 ~]# service mysql stop
Shutting down MySQL... [ OK ]在管理节点上查看日志：
[root@ser6-51 ~]# tail -f /var/log/mha/app1/manager.log
----- Failover Report -----
app1: MySQL Master failover 192.168.6.51(192.168.6.51:3306) to 192.168.6.52(192.168.6.52:3306) succeeded
Master 192.168.6.51(192.168.6.51:3306) is down!
Check MHA Manager logs at ser6-51:/var/log/mha/app1/manager.log for details.
Started automated(non-interactive) failover.
The latest slave 192.168.6.52(192.168.6.52:3306) has all relay logs for recovery.
Selected 192.168.6.52(192.168.6.52:3306) as a new master.
192.168.6.52(192.168.6.52:3306): OK: Applying all logs succeeded.
192.168.6.70(192.168.6.70:3306): This host has the latest relay log events.
Generating relay diff files from the latest slave succeeded.
192.168.6.70(192.168.6.70:3306): OK: Applying all logs succeeded. Slave started, replicating from 192.168.6.52(192.168.6.52:3306)
192.168.6.52(192.168.6.52:3306): Resetting slave info succeeded.
Master failover to 192.168.6.52(192.168.6.52:3306) completed successfully.可以看到master自动切换到6.54上了。
在55上查看：
mysql> show slave status \G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.6.52
Master_User: rep_user
Master_Port: 3306可以看到master_host变成了192.168.168.54
在现在的master上查看变量read_only,发现被自动关闭了，说明之前的slave现在可写了：
mysql> show variables like 'read_only';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| read_only | OFF |
+---------------+-------+
1 row in set (0.01 sec)我发现再次启动6.51的mysql后，并没有自动加入集群。需要自己连接到现在的master上。
总结
- 在一台新的主机宕机之后，mha选用一台新的slave作为主机，那么预先要在这台主机上授权 GRANT REPLICATION SLAVE, REPLICATION CLIENT ON …
- 正式环境需要4台主机，才能更好的看出效果
一台管理机、一台主、两台从。因为当主挂掉之后，从slave中选出一台切换成master
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