前言
构建一个Mysql分布式集群需要对数据库的原理有较深的认识，而深奥复杂的数据库原理往往让很多读者中途放弃。本系列尝试用最简单的语言介绍Mysql分布式集群涉及到的原理，并结合实践的方式给读者介绍如何构建一个Mysql分布式集群。
目录
1.Mysql分布式集群（一）主从复制
2.Mysql分布式集群（二）主主复制和高可用
主从复制
主从复制是为了完成一个和主数据库一致的数据库，当主数据数据改变的时候，从数据库自动保持和主数据库一致的改变。主从复制主要应用于读写分离，数据库备份。
实验环境：
Master ip :192.168.178.128
Slave ip :192.168.179.129
操作系统：Ubuntu14.04
mysql版本：5.7.20
主从复制原理
主从复制既能在程序端完成也能在Mysql端完成，本系列主要介绍通过配置Mysql 完成主从复制。具体原理如下图所示：
主从复制原理
1.Master对数据改变之后，会将记录改变的事件（如：delete,update等）在Master中的Binary log（以下称：bin log）；
2.Slave会按照一定的频率使用I/Othread读取Master上的bin log，并将该日志中的最近改变事件，写到Relay log（中继日志）中；
3.Salve通过SQL Thread 读取Relay log ,将改变事件同步到自己的Mysql中；
Master端配置
根据以上的原理可以，Slave端需要读取Master端的bin log日志，因此需要再Master端完成以下工作：
1.对远程访问Master数据库的用户授权。
默认情况下root只能在本地登录，只有授权了，Slave端才能读取Master端bin log日志。
mysql> select host,user from mysql.user;
+-----------+---------------+
| host | user |
+-----------+---------------+
| localhost | mysql.session |
| localhost | mysql.sys |
| localhost | root |
+-----------+---------------+
mysql> grant all on *.* to 'slave'@'192.168.179.129' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.02 sec)
mysql> select user,host from mysql.user;
+---------------+-----------------+
| user | host |
+---------------+-----------------+
| slave | 192.168.179.129 |
| mysql.session | localhost |
| mysql.sys | localhost |
| root | localhost |
+---------------+-----------------+
mysql> show grants for 'salve'@192.168.179.129;
+----------------------------------------------------------+
| Grants for [email protected] |
+----------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'salve'@'192.168.179.129' |
+----------------------------------------------------------+
1 row in set (0.00 sec)
以上我们授予slave用户所有库所有表的权限.
然后可以在Slave端使用用户slave远程登录一下Master端的数据库，检查是否能远程登录：
root@ubuntu:~# mysql -uslave -p -h192.168.179.128;
Enter password:
ERROR 2003 (HY000): Can't connect to MySQL server on '192.168.179.128' (111)
如果遇到以上的问题，在能ping通Master的情况下，请检查两个方面：
1.Master端的防火墙是否关闭
root@ubuntu:~# ufw status;
Status: inactive
2.如果Master端的防火墙已关，则查看Mysql的bind_address变量
mysql> show variables like '%bind_address%';
+---------------+-----------+
| Variable_name | Value |
+---------------+-----------+
| bind_address | 127.0.0.1 |
+---------------+-----------+
1 row in set (0.02 sec)
可以发现bind_address 地址只允许本地访问，因此需要修改它，可以讲mysqld.cnf中注释掉bind-address，重启Mysql之后，在Slave端就可以正常连接了。
root@ubuntu:~# vim /etc/mysql/mysql.conf.d/mysqld.cnf
[mysqld]
# By default we only accept connections from localhost
#bind-address = 127.0.0.1
root@ubuntu:~# /etc/init.d/mysql restart
* Stopping MySQL Community Server 5.7.20
....
* MySQL Community Server 5.7.20 is stopped
* Re-starting MySQL Community Server 5.7.20
.........
* MySQL Community Server 5.7.20 is started
2.打开bin log日志
默认情况下Mysql是不开启这个日志的，如下：
mysql> show global variables like '%log_bin%';
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| log_bin | OFF |
| log_bin_basename | |
| log_bin_index | |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
+---------------------------------+-------+
打开bin log 可以通过在mysqld.cnf中指定log-bin路径完成，需要注意的是如果打开bin log 一定要指定server-id，否则重启Mysql会报错。
root@ubuntu:~# vim /etc/mysql/mysql.conf.d/mysqld.cnf
[mysqld]
......
#bind-address = 127.0.0.1
server-id=1
log-bin =/var/log/mysql/mysql-bin.log
......
重启Mysql之后，查看bin log日志状态
mysql> show global variables like '%log_bin%';
+---------------------------------+--------------------------------+
| Variable_name | Value |
+---------------------------------+--------------------------------+
| log_bin | ON |
| log_bin_basename | /var/log/mysql/mysql-bin |
| log_bin_index | /var/log/mysql/mysql-bin.index |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
+---------------------------------+--------------------------------+
5 rows in set (0.03 sec)
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 | 154 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.02 sec)
mysql> show master logs;
+------------------+-----------+
| Log_name | File_size |
+------------------+-----------+
| mysql-bin.000001 | 154 |
+------------------+-----------+
1 row in set (0.01 sec)
此时可以看到log_bin已经开启了。
我们可以使用mysqlbinlog命令对bin log日志进行操作，这里就不展开讲了。
Slave端配置
更改Slave的配置文件
root@ubuntu:~# vim /etc/mysql/mysql.conf.d/mysqld.cnf
[mysqld]
.......
server-id=2
relay_log = mysql-relay-bin
.......
需要注意的是server-id一定不要和Master中的server-id一样
mysql> change master to master_host='192.168.179.128',
-> master_user='slave',
-> master_password='123456',
-> master_log_file='mysql-bin.000001', master_log_pos=154;
Query OK, 0 rows affected, 2 warnings (0.34 sec)
通过以上的方式指定Master，这种方式的好处是不用重启服务器，也可以动态改变指向的Master。接下来启动Slave端
mysql> start slave;
Query OK, 0 rows affected (0.08 sec)
mysql> SHOW SLAVE STATUS\G
*************************** 1. row ***************************
Slave_IO_State:
Master_Host: 192.168.179.128
Master_User: slave
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000001
Read_Master_Log_Pos: 154
Relay_Log_File: mysql-relay-bin.000001
Relay_Log_Pos: 4
Relay_Master_Log_File: mysql-bin.000001
Slave_IO_Running: No
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: 154
Relay_Log_Space: 154
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: 1593
Last_IO_Error: Fatal error: The slave I/O thread stops because master and slave have equal MySQL server UUIDs; these UUIDs must be different for replication to work.
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID:
Master_Info_File: /var/lib/mysql/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: 171028 03:44:54
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
启动Slave的时候发现，Slave_IO_Running:No，在上文的原理中已经介绍了，Slave需要Slave_IO和Slave_SQL线程，但是此时IO线程没有开启。检查Slave状态发现了错误：
Last_IO_Error: Fatal error: The slave I/O thread stops because master and slave have equal MySQL server UUIDs; these UUIDs must be different for replication to work.
原来是Slave 和Master使用了一样的UUID
Master端UUID
mysql> show variables like '%UUID%';
+---------------+--------------------------------------+
| Variable_name | Value |
+---------------+--------------------------------------+
| server_uuid | d7c00798-b94e-11e7-8656-000c29f0d4cf |
+---------------+--------------------------------------+
1 row in set (0.02 sec)
Slave端UUID
mysql> show variables like '%UUID%';
+---------------+--------------------------------------+
| Variable_name | Value |
+---------------+--------------------------------------+
| server_uuid | d7c00798-b94e-11e7-8656-000c29f0d4cf |
+---------------+--------------------------------------+
1 row in set (0.02 sec)
可以发现，二者的UUID确实一样，此时可以更改其中一个的UUID，本文中选择修改Slave的UUID，如下：
root@ubuntu:~# vim /var/lib/mysql/auto.cnf
[auto]
server-uuid=d7c00798-b94e-11e7-8656-000c29f0d4ce
重启Slave端的Mysql后，发现Slave的IO线程也开启了。其中Id:1为SQL线程，Id:2位IO线程
mysql> show processlist\G
*************************** 1. row ***************************
Id: 1
User: system user
Host:
db: NULL
Command: Connect
Time: 3706
State: Slave has read all relay log; waiting for more updates
Info: NULL
*************************** 2. row ***************************
Id: 2
User: system user
Host:
db: NULL
Command: Connect
Time: 3706
State: Waiting for master to send event
Info: NULL
*************************** 3. row ***************************
Id: 6
User: root
Host: localhost
db: NULL
Command: Query
Time: 0
State: starting
Info: show processlist
3 rows in set (0.00 sec)
以上完成了Slave端的配置
验证主从是否成功
1.创建数据库
Master端创建数据库
mysql> create database test;
Query OK, 1 row affected (0.28 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
5 rows in set (0.02 sec)
Slave 端查询数据库是否同步
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
5 rows in set (0.01 sec)
可以发现Slave端也创建了test库
2.创建表并插入数据
Master端
mysql> use test;
Database changed
mysql> create table user(id int(3),name varchar(10));
Query OK, 0 rows affected (1.84 sec)
mysql> insert into user values(001,'kevin');
Query OK, 1 row affected (0.02 sec)
mysql> select * from user;
+------+-------+
| id | name |
+------+-------+
| 1 | kevin |
+------+-------+
1 row in set (0.04 sec)
Salve端
mysql> use test;
Database changed
mysql> create table user(id int(3),name varchar(10));
Query OK, 0 rows affected (1.84 sec)
mysql> insert into user values(001,'kevin');
Query OK, 1 row affected (0.02 sec)
mysql> select * from user;
+------+-------+
| id | name |
+------+-------+
| 1 | kevin |
+------+-------+
1 row in set (0.04 sec)
以上可以发现Slave已经自动完成了同步。此时已经完成了Mysql 主从复制。
补充：
如果在同步的过程中发现Slave节点不同步的话，可以通过以下操作完成同步
在Master端查看日志的状态，例如
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 | 1026 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
此时Master的Position指向1026，我们需要在Slave节点中重新指向该位置
mysql> stop slave;
Query OK, 0 rows affected (0.07 sec)
mysql> change master to master_host='192.168.179.128',
-> master_user='slave',
-> master_password='123456',
-> master_log_file='mysql-bin.000001', master_log_pos=1026;
Query OK, 0 rows affected, 2 warnings (0.34 sec)
mysql> start slave;
Query OK, 0 rows affected (0.03 sec)
通过以上的重新指定，则可以重新同步。