MySQL主主+Keepalived
MySQL+DRBD+Heartbeat
在企業中，數據庫高可用一直是企業的重中之重，中小企業很多都是使用mysql主主方案，一主多從，讀寫分離等，但是單主存在單點故障，從庫切換成主庫需要作改動。因此，如果是雙主或者多主，就會增加mysql入口，增加高可用。不過多主需要考慮自增長ID問題，這個需要特別設置配置文件，比如雙主，可以使用奇偶，總之，主之間設置自增長ID相互不沖突就能完美解決自增長ID沖突問題。
主主方案實現思路
1、 兩台mysql都可讀寫，互為主備。默認只使用一台masterA負責數據的寫入，另一台masterB備用處於備用狀態；
2、 masterA是masterB的主庫，masterB又是masterA的主庫，它們互為主從；
3、 兩台主庫之間做高可用,可以采用keepalived等方案，使用VIP對外提供服務；
4、所有提供服務的從服務器與masterB進行主從同步（雙主多從）;
5、建議采用高可用策略的時候，masterA或masterB均不因宕機恢復后而搶占VIP（非搶占模式）；
這樣做可以在一定程度上保證主庫的高可用,在一台主庫down掉之后,可以在極短的時間內切換到另一台主庫上，盡可能減少主庫宕機對業務造成的影響，減少了主從同步給生產主庫帶來的壓力；
但是也有幾個不足的地方:
- masterB可能會一直處於空閑狀態（可以用它當從庫，負責部分查詢）；
- 主庫后面提供服務的從庫要等masterB先同步完了數據后才能去masterB上去同步數據，這樣可能會造成一定程度的同步延時；
第1台機器
[root@localhost ~]# vim /etc/my.cnf
[mysqld]
server-id=1
log-bin=mysql-binlog #打開二進制功能
log-slave-updates=true
max_binlog_size=1024M #binlog單文件最大值
auto_increment_offset = 1
auto_increment_increment = 2 #奇數ID
replicate-ignore-db = information_schema #忽略不同步主從的數據庫
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 #忽略應用程序想要設置的其他字符集
init-connect='SET NAMES utf8' #連接時執行的SQL
character-set-server=utf8 #服務端默認字符集
wait_timeout=1800 #請求的最大連接時間
interactive_timeout=1800 #和上一參數同時修改才會生效
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES #sql模式
relay-log=relay-log-bin #開啟中繼日志
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台機器
[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 #偶數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)
特別參數說明
log-slave-updates = true #將復制事件寫入binlog,一台服務器既做主庫又做從庫此選項必須要開啟
masterA自增長ID
auto_increment_offset = 1
auto_increment_increment = 2 #奇數ID
masterB自增加ID
auto_increment_offset = 2
auto_increment_increment = 2 #偶數ID
測試環境，可以保證沒數據寫入。否則需要的步驟是：先masterA鎖表-->masterA備份數據-->masterA解鎖表 -->masterB導入數據-->masterB設置主從-->查看主從
第1台機器
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 status\G;
*************************** 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台機器
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 status\G;
*************************** 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台機器
MariaDB [(none)]> create database test01;
Query OK, 1 row affected (0.01 sec)
第2台機器
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台機器
MariaDB [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
| test01 |
| test02 |
+--------------------+
6 rows in set (0.00 sec)