下面来学习：1、数据库层面的主从配置实现
2、代码层面的读写分离实现
主从同步工作原理：
先去阿里云买两个云服务器，然后重置密码，重启服务器，接着用Xshell远程连接。
下面介绍阿里云Centos7使用yum安装MySQL5.6（这里也介绍另外一个博客：http://blog.csdn.net/u011627980/article/details/52691799）：
[root@izwz99cwe60vsuzvi7ucuez ~]# rpm -Uvh http://dev.mysql.com/get/mysql-community-release-el7-5.noarch.rpm [root@izwz99cwe60vsuzvi7ucuez ~]# yum repolist enabled | grep "mysql.*-community.*" [root@izwz99cwe60vsuzvi7ucuez ~]# yum -y install mysql-community-server [root@izwz99cwe60vsuzvi7ucuez ~]# systemctl enable mysqld [root@izwz99cwe60vsuzvi7ucuez ~]# systemctl start mysqld [root@izwz99cwe60vsuzvi7ucuez ~]# mysql_secure_installation Enter current password for root (enter for none): OK, successfully used password, moving on... Setting the root password ensures that nobody can log into the MySQL root user without the proper authorisation. Set root password? [Y/n] y New password: Re-enter new password: Password updated successfully! Reloading privilege tables.. ... Success! By default, a MySQL installation has an anonymous user, allowing anyone to log into MySQL without having to have a user account created for them. This is intended only for testing, and to make the installation go a bit smoother. You should remove them before moving into a production environment. Remove anonymous users? [Y/n] y ... Success! Normally, root should only be allowed to connect from 'localhost'. This ensures that someone cannot guess at the root password from the network. Disallow root login remotely? [Y/n] n ... skipping. By default, MySQL comes with a database named 'test' that anyone can access. This is also intended only for testing, and should be removed before moving into a production environment. Remove test database and access to it? [Y/n] y - Dropping test database... ERROR 1008 (HY000) at line 1: Can't drop database 'test'; database doesn't exist ... Failed! Not critical, keep moving... - Removing privileges on test database... ... Success! Reloading the privilege tables will ensure that all changes made so far will take effect immediately. Reload privilege tables now? [Y/n] y ... Success!
OK，下面我已经弄好了两台服务器：120.78.146.32:22（从）和39.108.63.239:22（主）
接下来继续在主服务器中：
[root@izuct94rafpg7bz ~]# mysql -uroot -p mysql> show databases; mysql> exit [root@izuct94rafpg7bz ~]# vim /etc/my.cnf
敲击键盘i，表示输入模式：
加入三行即可：
server-id=1 log-bin=master-bin log-bin-index=master-bin.index
然后ctrl+c退出编辑模式，输入:wq保存退出。
接着重启mysql服务：
[root@izuct94rafpg7bz ~]# service mysqld restart
下面验证看有没有生效：
[root@izuct94rafpg7bz ~]# mysql -uroot -p mysql> show databases; mysql> show master status;
在从服务器中：
加入三行：
server-id=2 relay-log=slave-relay-bin relay-log-index=slave-relay-bin.index
另外一种重启方式（centos）：
[root@izwz99cwe60vsuzvi7ucuez ~]# service mysqld stop [root@izwz99cwe60vsuzvi7ucuez ~]# service mysqld start
[root@izwz99cwe60vsuzvi7ucuez ~]# mysql -uroot -p
先在主库中创建user，授权并刷新：
mysql> create user repl; mysql> grant replication slave on *.* to 'repl'@'120.78.146.32' identified by '你数据库的密码';
mysql> flush privileges;
从库：
mysql> change master to master_host='39.108.63.239',master_port=3306,master_user='repl',master_password='你数据库的密码',master_log_file='master-bin.000001',master_log_pos=0;
（注意这里master_log_file需要在主库中输入mysql> show master status）
mysql> start slave; mysql> show slave statusG
如果发现有问题的话：
mysql> stop slave mysql> exit [root@izwz99cwe60vsuzvi7ucuez ~]# start slave [root@izwz99cwe60vsuzvi7ucuez ~]# mysql -uroot -p show slave statusG
再看看是不是好了,如果还是不行，那就是防火墙端口没有开放的问题，这个问题很坑，不要踩。
以下这种就证明成功了：
下面来试验一下：
在主库中：
mysql> create database o2o; mysql> show databases;
在从库中：
mysql> show databases
这里要注意不要在从库写数据，因为不能同步到主库中，从库是用来读数据的，另外从库的mysql版本要比主库高，因为Mysql向后兼容，也就是说低版本语句的可以在高版本执行。
接下来我们把数据库的sql从本地导出，注意我本地是windows系统：
首先配置环境变量：http://jingyan.baidu.com/article/f7ff0bfc169a2a2e27bb1365.html 这里介绍的很清楚了
然后打开cmd，输入命令mysqldump -uroot -p o2o > o2o.sql，找到对应的目录下的文件o2o.sql
接下来使用Xftp5来传输文件上去。
mysql> show databases; mysql> use o2o mysql> source ~/o2o.sql mysql> show tables;
在主库和从库中分别执行：
mysql> grant select, insert, update,delete on *.* to 'work' identified by '230230' with grant option; mysql> flush privileges;
接下来改动项目的配置文件：
jdbc.driver=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://39.108.63.239:3306/o2o?useUnicode=true&characterEncoding=utf8 jdbc.username=work jdbc.password=230230
再运行测试方法：
成功。