一、Keepalived+MySQL Replication的应用场景
MySQL的高可用方案有cluster，MMM,MHA等，这些高可用方案都要三台服务器以上，成本有点高，今天介绍一个低成本高可用方案：MySQL Replication+keepalive这个方案只需要两台服务器，适合小型企业
二、Keepalived双机热备的优缺点
MySQL Replication 架构为master/master，其中一台设置为只读（read_only），当master1故障时，借助keepalive将vip漂移到master2上。继续提供服务。
优点：数据同步非常简单，实现起来相对复杂维护难度低
缺点：MySQL复制是异步的（虽然后面有了半同步），如果主库压力比较大，从库SQL线程目前MySQL的版本是单线程的，延时会比较大，因为同步延时大，当VIP发生切换时候，这个时候两台服务器的数据数据不一致。不过可以借助脚本，比如等SQL线程应用完中继日志以后再关闭read_only提供写服务。然后sync_binlog,innodb_flush_log_at_trx_commit都设置为1，日常监控复制延时，可以尽量避免这个情况，还有一个就是备机处于闲置状态。
三、配置MySQL双主
1.在maseter1里面配置复制帐号以及开启二进制日志，配置日志刷盘相关参数,并且做个全备
在my.cnf:[mysqld]段加上这几个参数
log_bin=dg6-log-bin
log_slave_updates=1
sync_binlog=1
server_id =11
innodb_flush_log_at_trx_commit=1
grant replication slave,replication client on *.* to repl@'192.168.80.%' identified by 'repl';
mysqldump -uroot -p1qaz2wsx -A -R --triggers --single-transaction --opt --master-data=2 > all.sql
如果是已经在跑的MySQL库，而且库很大，建议用Xtrabackup用流方式备份并传输到备库
2.在master2上配置复制相关参数
log_bin=dg7-log-bin
log_slave_updates=1
sync_binlog=1
server_id =12
innodb_flush_log_at_trx_commit=1
3.在master2上恢复备份，并且设置主从复制，复制信息已经在备份里面已经有了，根据这个信息设置主从复制。
[root@dg7 ~]# cat all.sql | grep ^"--" | grep -i change
-- CHANGE MASTER TO MASTER_LOG_FILE='dg6-logbin.000001', MASTER_LOG_POS=2438;
mysql> CHANGE MASTER TO MASTER_LOG_FILE='dg6-logbin.000001', MASTER_LOG_POS=2438,MASTER_HOST='192.168.80.106',MASTER_USER='repl',MASTER_PASSWORD='repl';
Query OK, 0 rows affected (0.01 sec)
mysql> start slave;
Query OK, 0 rows affected (0.01 sec)
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.80.106
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: dg6-logbin.000001
Read_Master_Log_Pos: 2438
Relay_Log_File: dg7-relay-bin.000002
Relay_Log_Pos: 254
Relay_Master_Log_File: dg6-logbin.000001
Slave_IO_Running: Yes
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: 2438
Relay_Log_Space: 408
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: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
1 row in set (0.00 sec)
mysql>
4.在master1上配置复制master2上面的信息
因为开启log_slave_updates参数，应用中继日志以后，也会写到本地的二进制日志，所以Position会不停的变动，不知道哪个为准，其实用哪个Position都没关系，master1都不会去应用，因为复制的SQL线程不会去应用serverid是自己本身的中继日志，所以只要在master2上show一把就行了。
mysql> show master status\G
*************************** 1. row ***************************
File: dg7-logbin.000001
Position: 542168
Binlog_Do_DB:
Binlog_Ignore_DB:
1 row in set (0.00 sec)
这就是我们需要的信息
mysql> CHANGE MASTER TO MASTER_LOG_FILE=' dg7-logbin.000001', MASTER_LOG_POS=542168,MASTER_HOST='192.168.80.107',MASTER_USER='repl',MASTER_PASSWORD='repl';
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.80.107
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: dg7-logbin.000001
Read_Master_Log_Pos: 542168
Relay_Log_File: dg6-relay-bin.000002
Relay_Log_Pos: 254
Relay_Master_Log_File: dg7-logbin.000001
Slave_IO_Running: Yes
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: 542168
Relay_Log_Space: 408
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: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 11
1 row in set (0.00 sec)
四、 安装配置keepalvie
1.wget http://www.keepalived.org/software/keepalived-1.2.13.tar.gz
[root@dg6 ~]# tar xf keepalived-1.2.13.tar.gz
[root@dg6 ~]# cd keepalived-1.2.13
[root@dg6 keepalived-1.2.13]# ./configure --prefix=/usr/local/keepalive
checking for gcc... gcc checking whether the C compiler works... yes checking for C compiler default output file name... a.out checking for suffix of executables... checking whether we are cross compiling... no checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking for a BSD-compatible install... /usr/bin/install -c checking for strip... strip checking how to run the C preprocessor... gcc -E checking for grep that handles long lines and -e... /bin/grep checking for egrep... /bin/grep -E checking for ANSI C header files... yes checking for sys/wait.h that is POSIX.1 compatible... yes checking for sys/types.h... yes checking for sys/stat.h... yes checking for stdlib.h... yes checking for string.h... yes checking for memory.h... yes checking for strings.h... yes checking for inttypes.h... yes checking for stdint.h... yes checking for unistd.h... yes checking fcntl.h usability... yes checking fcntl.h presence... yes checking for fcntl.h... yes checking syslog.h usability... yes checking syslog.h presence... yes checking for syslog.h... yes checking for unistd.h... (cached) yes checking sys/ioctl.h usability... yes checking sys/ioctl.h presence... yes checking for sys/ioctl.h... yes checking sys/time.h usability... yes checking sys/time.h presence... yes checking for sys/time.h... yes checking openssl/ssl.h usability... no checking openssl/ssl.h presence... no checking for openssl/ssl.h... no configure: error: !!! OpenSSL is not properly installed on your system. !!! !!! Can not include OpenSSL headers files. !!! 缺少openssl-devel包