在本文中，使用单机上多个实例来搭建一个主从集群。
基于的MySQL版本是5.7.27。
单机多实例的具体安装过程可参考文档单机安装MySQL多实例。
将要搭建的集群实例信息如下：
| 角色 | 端口 |
|---|---|
| 主库 | 3306 |
| 从库1 | 3307 |
| 从库2 | 3308 |
1.创建复制账号
在主库上，创建复制用的账号，并赋予相应权限：
mysql> CREATE USER 'rep'@'%' IDENTIFIED BY 'replication*001';
mysql> GRANT REPLICATION SLAVE ON *.* TO 'rep'@'%';
查看用户:
mysql> select host, user from mysql.user;
+-----------+---------------+
| host | user |
+-----------+---------------+
| % | rep |
| localhost | mysql.session |
| localhost | mysql.sys |
| localhost | root |
+-----------+---------------+
4 rows in set (0.00 sec)
mysql> show grants for 'rep'@'%';
+---------------------------------------------+
| Grants for rep@% |
+---------------------------------------------+
| GRANT REPLICATION SLAVE ON *.* TO 'rep'@'%' |
+---------------------------------------------+
1 row in set (0.00 sec)
2.设置从库指向主库
首先，清空从库1，从库2上的binlog日志位点信息：
reset master
注意，reset master 会清空日志文件及GTID信息，在生产环境谨慎操作！
这里是为了简便快速搭建集群才这样操作的。
接着，设置复制关系：
CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=3306, MASTER_USER='rep', MASTER_PASSWORD='replication*001', MASTER_AUTO_POSITION=1;
指定主从复制参数：主库的地址和端口，复制账号和密码，以及GTID参数。
启动复制:
start slave;
3.查看复制状态
在从库上，查看复制状态
mysql> show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 127.0.0.1
Master_User: rep
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000001
Read_Master_Log_Pos: 853
Relay_Log_File: relay-bin.000003
Relay_Log_Pos: 454
Relay_Master_Log_File: mysql-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: 853
Relay_Log_Space: 1567
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:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID: 43cf1658-41a4-11ea-9f90-080027974966
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: 43cf1658-41a4-11ea-9f90-080027974966:1-3
Executed_Gtid_Set: 43cf1658-41a4-11ea-9f90-080027974966:1-3
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
在主库上查看有哪些从库：
mysql> show slave hosts;
+-----------+------+------+-----------+--------------------------------------+
| Server_id | Host | Port | Master_id | Slave_UUID |
+-----------+------+------+-----------+--------------------------------------+
| 3 | | 3308 | 1 | 2bbf28c5-41a5-11ea-bf30-080027974966 |
| 2 | | 3307 | 1 | 254f18a1-41a5-11ea-be32-080027974966 |
+-----------+------+------+-----------+--------------------------------------+
2 rows in set (0.00 sec)
可以看到，主库有两个从库：从库1，从库2。