MySQL主主+Keepalived
MySQL+DRBD+Heartbeat
在企业中，数据库高可用一直是企业的重中之重，中小企业很多都是使用mysql主主方案，一主多从，读写分离等，但是单主存在单点故障，从库切换成主库需要作改动。因此，如果是双主或者多主，就会增加mysql入口，增加高可用。不过多主需要考虑自增长ID问题，这个需要特别设置配置文件，比如双主，可以使用奇偶，总之，主之间设置自增长ID相互不冲突就能完美解决自增长ID冲突问题。
主主方案实现思路
1、 两台mysql都可读写，互为主备。默认只使用一台masterA负责数据的写入，另一台masterB备用处于备用状态；
2、 masterA是masterB的主库，masterB又是masterA的主库，它们互为主从；
3、 两台主库之间做高可用,可以采用keepalived等方案，使用VIP对外提供服务；
4、所有提供服务的从服务器与masterB进行主从同步（双主多从）;
5、建议采用高可用策略的时候，masterA或masterB均不因宕机恢复后而抢占VIP（非抢占模式）；
这样做可以在一定程度上保证主库的高可用,在一台主库down掉之后,可以在极短的时间内切换到另一台主库上，尽可能减少主库宕机对业务造成的影响，减少了主从同步给生产主库带来的压力；
但是也有几个不足的地方:
- masterB可能会一直处于空闲状态（可以用它当从库，负责部分查询）；
- 主库后面提供服务的从库要等masterB先同步完了数据后才能去masterB上去同步数据，这样可能会造成一定程度的同步延时；
第1台机器
[root@localhost ~]# vim /etc/my.cnf
[mysqld]
server-id=1
log-bin=mysql-binlog #打开二进制功能
log-slave-updates=true
max_binlog_size=1024M #binlog单文件最大值
auto_increment_offset = 1
auto_increment_increment = 2 #奇数ID
replicate-ignore-db = information_schema #忽略不同步主从的数据库
replicate-ignore-db = performance_schema
replicate-ignore-db = test
replicate-ignore-db = mysql
max_connections = 3000
max_connect_errors = 30
skip-character-set-client-handshake #忽略应用程序想要设置的其他字符集
init-connect='SET NAMES utf8' #连接时执行的SQL
character-set-server=utf8 #服务端默认字符集
wait_timeout=1800 #请求的最大连接时间
interactive_timeout=1800 #和上一参数同时修改才会生效
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES #sql模式
relay-log=relay-log-bin #开启中继日志
relay-log-index=slave-relay-bin.index
[root@localhost ~]# systemctl restart mariadb
[root@localhost ~]# mysql
MariaDB [(none)]> grant replication slave on *.* to 'repl'@'192.168.200.112' identified by '123456';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show master status;
+---------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+---------------------+----------+--------------+------------------+
| mysql-binlog.000004 | 486 | | |
+---------------------+----------+--------------+------------------+
1 row in set (0.00 sec)
第2台机器
[root@localhost ~]# cat /etc/my.cnf
[mysqld]
server-id = 2
log-bin=mysql-binlog
log-slave-updates=true
max_binlog_size=1024M
auto_increment_offset = 2
auto_increment_increment = 2 #偶数ID
replicate-ignore-db = information_schema
replicate-ignore-db = performance_schema
replicate-ignore-db = test
replicate-ignore-db = mysql
max_connections = 3000
max_connect_errors = 30
skip-character-set-client-handshake
init-connect='SET NAMES utf8'
character-set-server=utf8
wait_timeout=1800
interactive_timeout=1800
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
relay-log=relay-log-bin
relay-log-index=slave-relay-bin.index
[root@localhost ~]# systemctl restart mariadb
[root@localhost ~]# mysql
MariaDB [(none)]> grant replication slave on *.* to 'repl'@'192.168.200.111' identified by '123456';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> flush privileges;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show master status;
+---------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+---------------------+----------+--------------+------------------+
| mysql-binlog.000001 | 889 | | |
+---------------------+----------+--------------+------------------+
1 row in set (0.00 sec)
特别参数说明
log-slave-updates = true #将复制事件写入binlog,一台服务器既做主库又做从库此选项必须要开启
masterA自增长ID
auto_increment_offset = 1
auto_increment_increment = 2 #奇数ID
masterB自增加ID
auto_increment_offset = 2
auto_increment_increment = 2 #偶数ID
测试环境，可以保证没数据写入。否则需要的步骤是：先masterA锁表-->masterA备份数据-->masterA解锁表 -->masterB导入数据-->masterB设置主从-->查看主从
第1台机器
MariaDB [(none)]> stop slave;
Query OK, 0 rows affected, 1 warning (0.00 sec)
MariaDB [(none)]> change master to master_host='192.168.200.112',master_port=3306,master_user='repl',master_password='123456',master_log_file='mysql-binlog.000001',master_log_pos=889;
Query OK, 0 rows affected (0.04 sec)
MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> show slave statusG;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.200.112
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-binlog.000001
Read_Master_Log_Pos: 889
Relay_Log_File: relay-log-bin.000002
Relay_Log_Pos: 532
Relay_Master_Log_File: mysql-binlog.000001
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
第2台机器
MariaDB [(none)]> stop slave;
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> change master to master_host='192.168.200.111',master_port=3306,master_user='repl',master_password='123456',master_log_file='mysql-binlog.000004',master_log_pos=486;
Query OK, 0 rows affected (0.13 sec)
MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> show slave statusG;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.200.111
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-binlog.000004
Read_Master_Log_Pos: 486
Relay_Log_File: relay-log-bin.000002
Relay_Log_Pos: 532
Relay_Master_Log_File: mysql-binlog.000004
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
第1台机器
MariaDB [(none)]> create database test01;
Query OK, 1 row affected (0.01 sec)
第2台机器
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
| test01 |
+--------------------+
5 rows in set (0.00 sec)
MariaDB [(none)]> create database test02;
Query OK, 1 row affected (0.00 sec)
第1台机器
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
| test01 |
| test02 |
+--------------------+
6 rows in set (0.00 sec)