MySQL高可用目前有heartbeat+drbd、MHA、MySQL复制等几种较成熟的方案，heartbeat+drbd的方案可扩展性较差，而且读写都由主服务器负责，从库并不提供读功能，适合于数据增长量不大、一致性要求很高的环境，如银行、金融业等。今天重点讲下MHA的高可用架构。

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  MHA是一款优秀的高可用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0-30秒之内自动完成数据库的故障切换，并且在切换的过程中，大限度的保证数据的一致性，以达到真正意义上的高可用。MHA高可用建立在MySQL主从复制的基础上，先了解下MySQL复制最常见的两种方式：

• 异步复制：主库写入并提交事务之后，把记录写进主库二进制日志即返回客户端，主库和从库的数据存在一定的延迟，这样就存在一定的隐患，当主库提交了一个事务，并且写入了二进制日志，而从库尚未得到主库推送的二进制日志时，此时主库宕机，将造成主从服务器的数据不一致。

• 半同步复制：主库在每次提交事务成功时，并不及时反馈给客户端，而是等待其中一个从库也接收到二进制日志并写入中继日志之后，才返回操作成功给客户端。

  MHA组成：

• MHA Manager：管理节点，可以单独的部署在一台独立的服务器上，管理多个master-slave集群，也可以部署在一台Slave上。

• MHA Node：数据节点，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master，然后将其它所有的slave重新指向新的master。整个故障转移过程对应用程序是完全透明的。

  MHA工作原理：

1）从宕机的master保存二进制日志事件

2）识别含有最新更新的Slave

3) 应用差异的中继日志到其它从服务器

4）应用从master保存的二进制日志事件

5）提升一个新的Slave为master

6）使其它的Slave连接到新的master并复制

示例：MHA高可用架构（如果在内网可以关闭防火墙，否则请开启相应的端口）

Manager:node1：192.168.154.128

Master：node2：192.168.154.156

Slave：node3：192.168.154.130

Slave：node4：192.168.154.154

一 配置主从复制：

1）主节点：

[root@node2 ~]# vim /etc/my.cnf

innodb_file_per_table=1        #开启独立的表空间

skip_name_resolve         #禁止域名解析

log-bin=master-bin

relay-log=relay-bin

server-id=1

[root@node2 ~]# service mysqld restart

查看二进制日志信息

mysql> show master status;

+-------------------+----------+--------------+------------------+

| File        | Position | Binlog_Do_DB | Binlog_Ignore_DB |

+-------------------+----------+--------------+------------------+

| master-bin.000001 |    106 |        |          |

+-------------------+----------+--------------+------------------+

1 row in set (0.00 sec)

建立授权用户：

mysql> grant replication slave,replication client on *.* to 'slave'@'192.168.154.%' identified by 'slave';

Query OK, 0 rows affected (0.06 sec)

mysql> flush privileges;

Query OK, 0 rows affected (0.00 sec)

2）从节点：

[root@node3 ~]# vim /etc/my.cnf

innodb_file_per_table=1

skip_name_resolve

log-bin=slave-bin

relay-log=relay-bin

server_id=2

read_only=1

relay_log_purge=0

[root@node3 ~]# service mysqld restart

[root@node4 ~]# vim /etc/my.cnf

innodb_file_per_table=1

skip_name_resolve

log-bin=slave-bin

relay-log=relay-bin

server_id=3

read_only=1                    #开启只读模式

relay_log_purge=0             #关闭自动清理中继日志

[root@node4 ~]# service mysqld restart

设置同步：

mysql> change master to master_host='192.168.154.156',master_user='slave',master_password='slave',master_log_file='master-bin.000001',master_log_pos=106;

Query OK, 0 rows affected (0.03 sec)

mysql> start slave;

Query OK, 0 rows affected (0.01 sec)

mysql> show slave status\G

*************************** 1. row ***************************

        Slave_IO_State: Waiting for master to send event

         Master_Host: 192.168.154.156

         Master_User: slave

         Master_Port: 3306

        Connect_Retry: 60

       Master_Log_File: master-bin.000001

     Read_Master_Log_Pos: 354

        Relay_Log_File: relay-bin.000002

        Relay_Log_Pos: 500

    Relay_Master_Log_File: master-bin.000001

       Slave_IO_Running: Yes

      Slave_SQL_Running: Yes

       Replicate_Do_DB:

     Replicate_Ignore_DB:

      Replicate_Do_Table:

    Replicate_Ignore_Table:

   Replicate_Wild_Do_Table:

 Replicate_Wild_Ignore_Table:

          Last_Errno: 0

          Last_Error:

         Skip_Counter: 0

     Exec_Master_Log_Pos: 354

       Relay_Log_Space: 649

       Until_Condition: None

        Until_Log_File:

        Until_Log_Pos: 0

      Master_SSL_Allowed: No

      Master_SSL_CA_File:

      Master_SSL_CA_Path:

       Master_SSL_Cert:

      Master_SSL_Cipher:

        Master_SSL_Key:

    Seconds_Behind_Master: 0

Master_SSL_Verify_Server_Cert: No

        Last_IO_Errno: 0

        Last_IO_Error:

        Last_SQL_Errno: 0

        Last_SQL_Error:

1 row in set (0.00 sec)

3）在master节点上创建具有管理权限的账号

mysql> grant all on *.* to 'zwj'@'192.168.154.%' identified by 'zwj';

Query OK, 0 rows affected (0.00 sec)

二 配置集群间的密钥登陆

在node1上：

[root@node1 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.156

[root@node1 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.130

[root@node1 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.154

[root@node1 ~]# ssh 192.168.154.154 'ifconfig'            #验证

eth0    Link encap:Ethernet  HWaddr 00:0C:29:67:65:ED

     inet addr:192.168.154.154  Bcast:192.168.154.255  Mask:255.255.255.0

     inet6 addr: fe80::20c:29ff:fe67:65ed/64 Scope:Link

     UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

     RX packets:26253 errors:0 dropped:0 overruns:0 frame:0

     TX packets:42416 errors:0 dropped:0 overruns:0 carrier:0

     collisions:0 txqueuelen:1000

     RX bytes:23453164 (22.3 MiB)  TX bytes:2514457 (2.3 MiB)

     Interrupt:19 Base address:0x2024

在node2上：

[root@node2 ~]# ssh-keygen -t rsa

[root@node2 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.128

[root@node2 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.130

[root@node2 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.154

在node3上：

[root@node3 log]# ssh-keygen -t rsa

[root@node3 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.128

[root@node3 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.156

[root@node3 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.154

在node4上：

[root@node4 ~]# ssh-keygen -t rsa

[root@node4 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.128

[root@node4 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.156

[root@node4 ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.154.130

三 安装MHA Manager，在node1上：

[root@node1 ~]# yum install perl-DBD-MySQL -y

[root@node1 ~]# tar -zxf mha4mysql-node-0.56.tar.gz

[root@node1 ~]# cd mha4mysql-node-0.56

[root@node1 mha4mysql-node-0.56]# perl Makefile.PL

[root@node1 mha4mysql-node-0.56]# make

[root@node1 mha4mysql-node-0.56]# make install

[root@node1 mha4mysql-manager-0.56]# yum install perl-DBD-MySQL perl-Config-Tiny perl-Log-Dispatch perl-Parallel-ForkManager perl-Time-HiRes -y        #安装MHA Manger依赖的perl模块

[root@node1 ~]# tar -zxf mha4mysql-manager-0.56.tar.gz

[root@node1 ~]# cd mha4mysql-manager-0.56

[root@node1 mha4mysql-manager-0.56]# perl Makefile.PL

[root@node1 mha4mysql-manager-0.56]# make

[root@node1 mha4mysql-manager-0.56]# make install

四 安装MySQL node（在所有MySQL服务器上）

[root@node2 ~]#yum install perl-DBD-MySQL -y

[root@node2 ~]# cd mha4mysql-node-0.56/

[root@node2 mha4mysql-node-0.56]# perl Makefile.PL

[root@node2 mha4mysql-node-0.56]# make

[root@node2 mha4mysql-node-0.56]# make install

五 创建工作目录，配置MHA:

[root@node1 ~]# mkdir -pv /etc/masterha

[root@node1 ~]# vim /etc/masterha/appl.cnf

[server default]

user=zwj

password=zwj

manager_workdir=/etc/masterha/appl

manager_log=/etc/masterha/appl/manager.log

remote_workdir=/etc/masterha/appl

ssh_user=root

repl_user=slave

repl_password=slave

ping_interval=1

[server1]

hostname=192.168.154.156

[server2]

hostname=192.168.154.130

candidate_master=1                        #设置为备选的master

[server3]

hostname=192.168.154.154

六 检查SSH连接状态：

[root@node1 ~]# masterha_check_ssh --conf=/etc/masterha/appl.cnf

Wed May 10 00:12:58 2017 - [warning] Global configuration file /etc/masterha_default.cnf not found. Skipping.

Wed May 10 00:12:58 2017 - [info] Reading application default configuration from /etc/masterha/appl.cnf..

Wed May 10 00:12:58 2017 - [info] Reading server configuration from /etc/masterha/appl.cnf..

Wed May 10 00:12:58 2017 - [info] Starting SSH connection tests..

Wed May 10 00:13:15 2017 - [debug]

Wed May 10 00:12:59 2017 - [debug]  Connecting via SSH from root@192.168.154.154(192.168.154.154:22) to root@192.168.154.156(192.168.154.156:22)..

Wed May 10 00:13:05 2017 - [debug]  ok.

Wed May 10 00:13:05 2017 - [debug]  Connecting via SSH from root@192.168.154.154(192.168.154.154:22) to root@192.168.154.130(192.168.154.130:22)..

Wed May 10 00:13:15 2017 - [debug]  ok.

Wed May 10 00:13:20 2017 - [debug]

Wed May 10 00:12:58 2017 - [debug]  Connecting via SSH from root@192.168.154.130(192.168.154.130:22) to root@192.168.154.156(192.168.154.156:22)..

Wed May 10 00:13:11 2017 - [debug]  ok.

Wed May 10 00:13:11 2017 - [debug]  Connecting via SSH from root@192.168.154.130(192.168.154.130:22) to root@192.168.154.154(192.168.154.154:22)..

Wed May 10 00:13:20 2017 - [debug]  ok.

Wed May 10 00:13:35 2017 - [debug]

Wed May 10 00:12:58 2017 - [debug]  Connecting via SSH from root@192.168.154.156(192.168.154.156:22) to root@192.168.154.130(192.168.154.130:22)..

Wed May 10 00:13:15 2017 - [debug]  ok.

Wed May 10 00:13:15 2017 - [debug]  Connecting via SSH from root@192.168.154.156(192.168.154.156:22) to root@192.168.154.154(192.168.154.154:22)..

Wed May 10 00:13:35 2017 - [debug]  ok.

Wed May 10 00:13:35 2017 - [info] All SSH connection tests passed successfully.

七 检查整个复制环境：

[root@node1 ~]# masterha_check_repl --conf=/etc/masterha/appl.cnf

...

192.168.154.156(192.168.154.156:3306) (current master)

 +--192.168.154.130(192.168.154.130:3306)

 +--192.168.154.154(192.168.154.154:3306)

Wed May 10 00:33:36 2017 - [info] Checking replication health on 192.168.154.130..

Wed May 10 00:33:36 2017 - [info]  ok.

Wed May 10 00:33:36 2017 - [info] Checking replication health on 192.168.154.154..

Wed May 10 00:33:36 2017 - [info]  ok.

Wed May 10 00:33:36 2017 - [warning] master_ip_failover_script is not defined.

Wed May 10 00:33:36 2017 - [warning] shutdown_script is not defined.

Wed May 10 00:33:36 2017 - [info] Got exit code 0 (Not master dead).

MySQL Replication Health is OK.

八 开启MHA Manager监控：

[root@node1 ~]# nohup masterha_manager --conf=/etc/masterha/appl.cnf > /etc/masterha/appl/manager.log 2>&1 &

[1] 8300

查看MHA Manager监控：

[root@node1 ~]# masterha_check_status --conf=/etc/masterha/appl.cnf

appl (pid:8300) is running(0:PING_OK), master:192.168.154.156

关闭MHA Manager监控：

[root@node1 ~]# masterha_stop --conf=/etc/masterha/appl.cnf

Stopped appl successfully.

[1]+  Exit 1          nohup masterha_manager --conf=/etc/masterha/appl.cnf > /etc/masterha/appl/manager.log 2>&1

九 模拟主库宕机：

[root@node2 ~]# service mysqld stop

Stopping mysqld:                      [  OK  ]

查看slave（node4），可见master已发生变化，

...

mysql> show slave status\G

*************************** 1. row ***************************

        Slave_IO_State: Waiting for master to send event

         Master_Host: 192.168.154.130

         Master_User: slave

         Master_Port: 3306

        Connect_Retry: 60

       Master_Log_File: slave-bin.000003

     Read_Master_Log_Pos: 106

        Relay_Log_File: relay-bin.000002

        Relay_Log_Pos: 251

    Relay_Master_Log_File: slave-bin.000003

       Slave_IO_Running: Yes

      Slave_SQL_Running: Yes

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