主从多用于网站架构，因为主从的同步机制是异步的，数据的同步有一定延迟，也就是说有可能会造成数据的丢失，但是性能比较好，因此网站大多数用的是主从架构的数据库，读写分离必须基于主从架构来搭建
1、配置准备
（1）yum源配置
[mariadb] name = MariaDB baseurl = http://mirrors.ustc.edu.cn/mariadb/yum/10.2/centos7-amd64/ gpgkey=http://mirrors.ustc.edu.cn/mariadb/yum/RPM-GPG-KEY-MariaDB gpgcheck=1
（2）服务器1：192.168.11.7（主）
服务器2：192.168.11.8（从）
2、修改配置文件
[root@ren7 ~]# vim /etc/my.cnf.d/server.cnf
[mysqld] server-id=1 <<主从节点必须保证不能一样 log-bin=mysql-bin
3、重启mysql服务
[root@ren7 ~]# systemctl restart mariadb
4、主节点上授权具有复制权限的用户（创建主从连接账号与授权）
MariaDB [(none)]> create user ‘slave01‘@‘%‘ identified by ‘123‘; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> grant replication slave on *.* to ‘slave01‘@‘%‘; Query OK, 0 rows affected (0.00 sec) MariaDB [(none)]> flush privileges; Query OK, 0 rows affected (0.00 sec)
5、查看当前二进制日志文件
MariaDB [(none)]> show master status; +------------------+----------+--------------+------------------+ | File | Position | Binlog_Do_DB | Binlog_Ignore_DB | +------------------+----------+--------------+------------------+ | mysql-bin.000001 | 781 | | | +------------------+----------+--------------+------------------+ 1 row in set (0.00 sec)
1、修改配置文件
[root@ren8 ~]# vim /etc/my.cnf.d/server.cnf ########################### [mysqld] server-id=2 ##########################
2、重启mysql服务
[root@ren8 ~]# service mariadb restart Redirecting to /bin/systemctl restart mariadb.service
3、登录数据库
[root@ren8 ~]# mysql_secure_installation [root@ren8 ~]# mysql -u root -p123 Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 24 Server version: 10.2.26-MariaDB MariaDB Server Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others. Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.
4、建立主从连接
格式：CHANGE MASTER TO 选项 选项： MASTER_HOST = ‘host_name‘ 指定主服务的ip或者主机名 MASTER_USER = ‘user_name‘ 指定主服务器的用户名 MASTER_PASSWORD = ‘password‘ 指定用户名的密码 MASTER_PORT = port_num 指定连接的端口，默认是3306 MASTER_CONNECT_RETRY = interval 指定连接失败的时候的重试间隔时间
MariaDB [(none)]> change master to master_host=‘192.168.11.7‘, master_user=‘slave01‘, master_password=‘123‘, master_log_file=‘mysql-bin.000001‘, master_log_pos=781; Query OK, 0 rows affected (0.03 sec)
5、启动从节点
MariaDB [(none)]> start slave; Query OK, 0 rows affected (0.00 sec)
6、查看从节点连接状态
主要看IO以及SQL线程是否启动
MariaDB [(none)]> show slave status\G; *************************** 1. row *************************** Slave_IO_State: Connecting to master Master_Host: 192.168.11.7 Master_User: slave01 Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000001 Read_Master_Log_Pos: 781 Relay_Log_File: ren8-relay-bin.000001 Relay_Log_Pos: 4 Relay_Master_Log_File: mysql-bin.000001 Slave_IO_Running: Connecting <<IO线程正在连接 Slave_SQL_Running: Yes <<SQL线程启动成功 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: 781 Relay_Log_Space: 256 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: NULL Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 2003 Last_IO_Error: error connecting to master ‘slave01@192.168.11.7:3306‘ - retry-time: 60 maximum-retries: 86400 message: Can‘t connect to MySQL server on ‘192.168.11.7‘ (113 "No route to host") Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 0 Master_SSL_Crl: Master_SSL_Crlpath: Using_Gtid: No Gtid_IO_Pos: Replicate_Do_Domain_Ids: Replicate_Ignore_Domain_Ids: Parallel_Mode: conservative SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it 1 row in set (0.00 sec) ERROR: No query specified
问题解决：
slave_IO_Running:Connecting一直处于连接状态
错误原因： 1、网络不通 2、账户密码错误 3、防火墙 4、mysql配置文件问题 5、连接服务器时语法错误 6、主服务器mysql权限
此处是防火墙的原因，在主从服务器上添加防火墙端口即可；
[root@ren7 ~]# firewall-cmd --add-port=3306/tcp success [root@ren7 ~]# firewall-cmd --add-port=3306/tcp --permanent success [root@ren8 ~]# firewall-cmd --add-port=3306/tcp success [root@ren8 ~]# firewall-cmd --add-port=3306/tcp --permanent success
MariaDB [(none)]> stop slave;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show slave status\G; *************************** 1. row *************************** Slave_IO_Running: Yes Slave_SQL_Running: Yes
7、测试
--在主节点创建一个新表 MariaDB [(none)]> create database zhong; Query OK, 1 row affected (0.00 sec) --在从节点查看是否创建成功 MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | zhong | +--------------------+ 4 rows in set (0.00 sec)
--如果出现不同步可以执行以下步骤
stop slave set GLOBAL SQL_SLAVE_SKIP_COUNTER=1; start slave
原文：https://www.cnblogs.com/renyz/p/11484954.html