memcached 集群单点故障解决方案

magent是一款开源的Memcached代理服务器软件，其项目网址为：

http://code.google.com/p/memagent/

一、安装步骤：
1、编译安装libevent：

wget http://monkey.org/~provos/libevent-1.4.9-stable.tar.gz
tar zxvf libevent-1.4.9-stable.tar.gz
cd libevent-1.4.9-stable/
./configure --prefix=/usr
make && make install
cd ../

2、编译安装Memcached：

wget http://danga.com/memcached/dist/memcached-1.2.6.tar.gz
tar zxvf memcached-1.2.6.tar.gz
cd memcached-1.2.6/
./configure --with-libevent=/usr
make && make install
cd ../

3、编译安装magent：

mkdir magent
cd magent/
wget http://memagent.googlecode.com/files/magent-0.5.tar.gz
tar zxvf magent-0.5.tar.gz
/sbin/ldconfig
sed -i "s#LIBS = -levent#LIBS = -levent -lm#g" Makefile
make
cp magent /usr/bin/magent
cd ../

二、使用实例：

memcached -m 1 -u root -d -l 127.0.0.1 -p 11211
memcached -m 1 -u root -d -l 127.0.0.1 -p 11212
memcached -m 1 -u root -d -l 127.0.0.1 -p 11213
magent -u root -n 51200 -l 127.0.0.1 -p 12000 -s 127.0.0.1:11211 -s 127.0.0.1:11212 -b 127.0.0.1:11213

1、分别在11211、11212、11213端口启动3个Memcached进程，在12000端口开启magent代理程序；
2、11211、11212端口为主Memcached，11213端口为备份Memcached；
3、连接上12000的magent，set key1和set key2，根据哈希算法，key1被写入11212和11213端口的Memcached，key2被写入11212和11213端口的Memcached；
4、当11211、11212端口的Memcached死掉，连接到12000端口的magent取数据，数据会从11213端口的Memcached取出；
5、当11211、11212端口的Memcached重启复活，连接到12000端口，magent会从11211或11212端口的 Memcached取数据，由于这两台Memcached重启后无数据，因此magent取得的将是空值，尽管11213端口的Memcached还有数据（此问题尚待改进）。


三、整个测试流程：

[root@centos52 ~]# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
stats
memcached agent v0.4
matrix 1 -> 127.0.0.1:11211, pool size 0
matrix 2 -> 127.0.0.1:11212, pool size 0
END
set key1 0 0 8
zhangyan
STORED
set key2 0 0 8
zhangyan
STORED
quit
Connection closed by foreign host.


[root@centos52 ~]# telnet 127.0.0.1 11211
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get key1
END
get key2
VALUE key2 0 8
zhangyan
END
quit
Connection closed by foreign host.


[root@centos52 ~]# telnet 127.0.0.1 11212
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get key1
VALUE key1 0 8
zhangyan
END
get key2
END
quit
Connection closed by foreign host.


[root@centos52 ~]# telnet 127.0.0.1 11213
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get key1
VALUE key1 0 8
zhangyan
END
get key2
VALUE key2 0 8
zhangyan
END
quit
Connection closed by foreign host.


模拟11211、11212端口的Memcached死掉
[root@centos52 ~]# ps -ef | grep memcached
root       6589     1   0 01:25 ?         00:00:00 memcached -m 1 -u root -d -l 127.0.0.1 -p 11211
root       6591     1   0 01:25 ?         00:00:00 memcached -m 1 -u root -d -l 127.0.0.1 -p 11212
root       6593     1   0 01:25 ?         00:00:00 memcached -m 1 -u root -d -l 127.0.0.1 -p 11213
root       6609   6509   0 01:44 pts/0     00:00:00 grep memcached
[root@centos52 ~]# kill -9 6589
[root@centos52 ~]# kill -9 6591
[root@centos52 ~]# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get key1
VALUE key1 0 8
zhangyan
END
get key2
VALUE key2 0 8
zhangyan
END
quit
Connection closed by foreign host.


模拟11211、11212端口的Memcached重启复活
[root@centos52 ~]# memcached -m 1 -u root -d -l 127.0.0.1 -p 11211
[root@centos52 ~]# memcached -m 1 -u root -d -l 127.0.0.1 -p 11212
[root@centos52 ~]# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get key1
END
get key2
END
quit
Connection closed by foreign host.