一、概念

　　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

二、配置主节点

1、配置准备

（1）yum源配置

[mysql57-community]
name=MySQL 5.7 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/7/$basearch/
enabled=1
gpgcheck=0

（2）服务器1：192.168.11.7（主）

　　  服务器2：192.168.11.8（从）

2、下载mysql，修改配置文件（5.7版本与mariadb冲突，需要先删除mariadb）

yum -y install mysql-com*server

[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 <<定义二进制日志文件保存文件和格式
binlog_format=row <<主从节点保持一致，要么都是row，要么都是mixed

3、重启mysql服务

[root@ren7 ~]# systemctl restart mysql

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）

mysql [(none)]> create user 'slave'@'%' identified by 'Slave123/';
Query OK, 0 rows affected (0.00 sec)

mysql [(none)]> grant replication slave on *.* to 'slave'@'%';
Query OK, 0 rows affected (0.00 sec)

mysql [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)

5、查看当前二进制日志文件

mysql [(none)]> show master status;
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 | 781 | | |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

三、配置从节点（修改从节点和主节点时间同步，可以使用NTP服务或者date直接设置）

1、修改配置文件

[root@ren8 ~]# vim /etc/my.cnf.d/server.cnf
###########################
[mysqld]
server-id=2
binlog_format=row
log-bin=mysql-bin
##########################

2、重启mysql服务

[root@ren8 ~]# service mysql restart
Redirecting to /bin/systemctl restart mysql

3、登录数据库

[root@ren8 ~]# mysql_secure_installation
[root@ren8 ~]# mysql -u root -p123
Welcome to the mysql monitor. Commands end with ; or \g.
Your mysql connection id is 24
Server version: 10.2.26-MariaDB mysql Server

Copyright (c) 2000, 2018, Oracle, mysql 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

mysql [(none)]> change master to master_host='192.168.11.7', master_user='slave', master_password='Slave123/', master_log_file='mysql-bin.000001', master_log_pos=781;
Query OK, 0 rows affected (0.03 sec)

5、启动从节点

mysql [(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

mysql [(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 'slave@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

　mysql [(none)]> stop slave;
　Query OK, 0 rows affected (0.00 sec)

　mysql [(none)]> start slave;
　Query OK, 0 rows affected (0.00 sec)

mysql [(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
mysql [(none)]> create database zhong;
Query OK, 1 row affected (0.00 sec)
--在从节点查看是否创建成功
mysql [(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