keepalived个人简单理解就是实现一个虚IP在keepalived主从服务器之间切换的功能，当主的keeplived挂掉，从机会无缝接管该虚IP。
keepalived它作为一个辅助实现高可用性工具，一般都会配合某个具体服务工作，例如mysql,drbd，haproxy等，本篇介绍的就是haproxy,在前期做好keepalived配置后，做一个切换脚本，当haproxy挂掉后，脚本会立即执行keepalived关闭操作，从而让从机接管,该虚IP其实会和本机的物理IP做绑定，访问虚IP其实就可以理解为访问本机物理IP，该虚IP会在脚本被触发后切换到从机，而后访问虚IP也就是在访问从机物理IP，从而实现haproxy的高可用性。
这个实验模拟的功能其实就是利用haproxy实现apache服务器间的负载均衡，缓解并发压力，并保证haproxy-master若挂掉,haproxy-backup能无缝接管，实现WEB站点负载均衡+高可用性。保证客户端无缝获取网站资源。
解决方案：
系统环境：centos6.3
apache: httpd-2.4.4
haproxy: haproxy-1.4.8
keepalived：keepalived-1.2.7
haproxy VIP: 192.168.7.70
haproxy-master(haproxy1): 192.168.7.71 ha1.example.com
haproxy-backup(haproxy2): 192.168.7.72 ha2.example.com
apache1: 192.168.7.73 www1.example.com
apache2: 192.168.7.74 www2.example.com
(haproxy1)为仅haproxy1配置
(haproxy2)为仅haproxy2配置
(haproxy1，haproxy2)为haproxy1和haproxy2都得配置
部署环境：
1.关闭iptables和SELINUX
# service iptables stop
# setenforce 0
# vi /etc/sysconfig/selinux
---------------
SELINUX=disabled
---------------
2.apache安装
配置详见传送门：http://showerlee.blog.51cto.com/2047005/1174141
注：haproxy+keepalived其实搭配nginx效果也不错，本人线上因为长期使用apache，所以这篇博文就以apache介绍为主。
安装完毕只需配置客户端浏览器访问根页面显示本机IP地址。
一.haproxy安装配置：(haproxy1，haproxy2)
# wget http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.8.tar.gz
# tar zxvf haproxy-1.4.8.tar.gz
# cd haproxy-1.4.8
# uname -a //查看linux内核版本
# make TARGET=linux26 PREFIX=/usr/local/haproxy
# make install PREFIX=/usr/local/haproxy
# useradd -s /sbin/nologin haproxy
# passwd haproxy
# chown -R haproxy.haproxy /usr/local/haproxy
配置：
# vi /usr/local/haproxy/haproxy.cfg
-----------------
global
log 127.0.0.1 local0
maxconn 5120
chroot /usr/local/haproxy
user haproxy
group haproxy
daemon
quiet
nbproc 1
pidfile /usr/local/haproxy/haproxy.pid
#启动服务后后会滚动日志，生产环境建议注释掉
debug
defaults
log 127.0.0.1 local3
mode http
option httplog
option httpclose
option dontlognull
#option forwardfor
option redispatch
retries 2
maxconn 2000
balance source
contimeout 5000
clitimeout 50000
srvtimeout 50000
listen web_proxy :80
server www1 192.168.7.73:80 weight 5 check inter 2000 rise 2 fall 5
server www2 192.168.7.74:80 weight 5 check inter 2000 rise 2 fall 5
listen stats :8888
mode http
#transparent
stats uri / haproxy-stats
stats realm Haproxy \ statistic
#认证
stats auth haproxy:password
-----------------
启动haproxy
# /usr/local/haproxy/sbin/haproxy -f /usr/local/haproxy/haproxy.cfg &
注：这里加上“&”是为了让haproxy服务后台运行，去掉“&”可实时查看其滚动日志
日志：
------------------------
Available polling systems :
sepoll : pref=400, test result OK
epoll : pref=300, test result OK
poll : pref=200, test result OK
select : pref=150, test result OK
Total: 4 (4 usable), will use sepoll.
Using sepoll() as the polling mechanism.
00000000:web_proxy.accept(0004)=0007 from [192.168.7.129:5752]
00000000:web_proxy.clireq[0007:ffff]: GET / HTTP/1.1
00000000:web_proxy.clihdr[0007:ffff]: Accept: text/html, application/xhtml+xml, */*
00000000:web_proxy.clihdr[0007:ffff]: Accept-Language: zh-CN
00000000:web_proxy.clihdr[0007:ffff]: User-Agent: Mozilla/5.0 (compatible; MSIE
9.0; Windows NT 6.1; WOW64; Trident/5.0)
00000000:web_proxy.clihdr[0007:ffff]: Accept-Encoding: gzip, deflate
00000000:web_proxy.clihdr[0007:ffff]: Host: 192.168.7.71
00000000:web_proxy.clihdr[0007:ffff]: If-Modified-Since: Tue, 28 May 2013 18:22:10
GMT
00000000:web_proxy.clihdr[0007:ffff]: If-None-Match: "10-4ddcb57ecf1ee"
00000000:web_proxy.clihdr[0007:ffff]: Connection: Keep-Alive
00000000:web_proxy.srvrep[0007:0008]: HTTP/1.1 304 Not Modified
00000000:web_proxy.srvhdr[0007:0008]: Date: Tue, 28 May 2013 19:48:35 GMT
00000000:web_proxy.srvhdr[0007:0008]: Server: Apache/2.4.4 (Unix)
00000000:web_proxy.srvhdr[0007:0008]: Connection: close
00000000:web_proxy.srvhdr[0007:0008]: ETag: "10-4ddcb57ecf1ee"
00000000:web_proxy.srvcls[0007:0008]
00000000:web_proxy.clicls[0007:0008]
00000000:web_proxy.closed[0007:0008]
------------------------
查看是否启动
# ps -ef|grep haproxy
--------------------------
haproxy 2255 1 0 03:33 ? 00:00:00 /usr/local/haproxy/sbin/haproxy -f
/usr/local/haproxy/haproxy.cfg
root 2323 2291 0 03:56 pts/1 00:00:00 grep haproxy
--------------------------
重启haproxy
# pkill haproxy
# /usr/local/haproxy/sbin/haproxy -f /usr/local/haproxy/haproxy.cfg
其中：
haproxy代理：192.168.7.71:80
apache1： 192.168.7.73:80
apache2： 192.168.7.74:80
统计页面监听的端口：8888
访问页面：
http://192.168.7.71:8888/haproxy-stats
认证账号/密码：haproxy/password
总结：
通过日志可以看出，客户端192.168.7.129连接haproxy192.168.7.71的80端口，且客户端无论如何刷新页面，haproxy都只会把访问请求跳转到apache2的192.168.7.74地址，这是因为balance source这个参数会保持会话ID,如果改成balance roundrobin模式，那么客户端会轮流连接两台web服务器，线上还是建议使用balance source,这样会保持某一客户端在长时间内保持他的会话，不会来回跳转。
这里其实已经利用haproxy完成了对两台apache服务器的负载均衡功能，但如何保证负载均衡的高可用性，这里就得利用keepalived的热备功能，保证haproxy1如果挂掉，haproxy2能实时接管，实现网站前端负载均衡高可用，这也是我们目前比较流行的组合haproxy+keepalived。
二.keepalived安装配置：(haproxy1，haproxy2）
# wget http://www.keepalived.org/software/keepalived-1.2.7.tar.gz
# tar zxvf keepalived-1.2.7.tar.gz
# cd keepalived-1.2.7
# ./configure --prefix=/usr/local/keepalived --with-kernel-
dir=/usr/src/kernels/2.6.32-279.el6.x86_64
# make && make install
设置keepalived启动脚本
# cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/rc.d/init.d/
# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
# mkdir /etc/keepalived
# cp /usr/local/keepalived/sbin/keepalived /usr/sbin/
# chkconfig keepalived on
(haproxy1）
# vi /etc/keepalived/keepalived.conf
----------------------
! Configuration File for keepalived
global_defs {
router_id LVS_DEVEL
}
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 51
priority 150
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.7.70
}
}
----------------------
(haproxy2）
# vi /etc/keepalived/keepalived.conf
----------------------
! Configuration File for keepalived
global_defs {
router_id LVS_DEVEL
}
vrrp_instance VI_1 {
state BACKUP
interface eth0
virtual_router_id 51
priority 120
advert_int 1
authentication {
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.7.70
}
}
----------------------
启动keepalived
# service keepalived start
# ps -ef |grep keepalived
----------------------
root 1726 1722 0 10:57 ? 00:00:00 sh /etc/keepalived/check_haproxy.sh
root 2678 1 0 11:15 ? 00:00:00 keepalived -D
root 2680 2678 0 11:15 ? 00:00:00 keepalived -D
root 2681 2678 0 11:15 ? 00:00:00 keepalived -D
root 2691 2178 0 11:15 pts/1 00:00:00 grep keepalived
-----------------------
创建haproxy+keepalived脚本：
实现当haproxy挂掉后，能再次启动haproxy,若无法再次启动则彻底关闭keepalived将VIP交给
从机处理。
(haproxy1，haproxy2）
# vi /etc/keepalived/check_haproxy.sh
---------------------
#!/bin/bash
while :
do
hapid=`ps -C haproxy --no-header |wc -l`
if [ $hapid -eq 0 ];then
/usr/local/haproxy/sbin/haproxy -f /usr/local/haproxy/haproxy.cfg
sleep 5
if [ $hapid -eq 0 ];then
/etc/init.d/keepalived stop
fi
fi
sleep 5
done
--------------------
改执行权限
# chmod 755 /etc/keepalived/check_haproxy.sh
强制后台执行（关闭客户端连接也会继续运行）
# nohup sh /etc/keepalived/check_haproxy.sh
注；该脚本参考酒哥的"构建高可用LINUX服务器"一书，需在keepalived开机正常启动后，方可在主从机执行。
本人实测，不能将该脚本做开机启动，会导致开机将keepalived服务关闭，如想实现开机自动执行该脚本，估计要做脚本语句优化，这里有兴趣的朋友可以帮忙修改一下。
三.测试：
1.在两台机器上分别执行ip add，目前显示VIP在haproxy1上与本机网卡绑定
(haproxy1）
# ip add
-----------------------
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen
1000
link/ether 00:0c:29:d2:c6:75 brd ff:ff:ff:ff:ff:ff
inet 192.168.7.71/24 brd 192.168.7.255 scope global eth0
inet 192.168.7.70/32 scope global eth0
inet6 fe80::20c:29ff:fed2:c675/64 scope link
valid_lft forever preferred_lft forever
-----------------------
(haproxy2）
# ip add
-----------------------
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen
1000
link/ether 00:0c:29:ff:21:19 brd ff:ff:ff:ff:ff:ff
inet 192.168.7.72/24 brd 192.168.7.255 scope global eth0
inet6 fe80::20c:29ff:feff:2119/64 scope link
valid_lft forever preferred_lft forever
-----------------------
在浏览器访问该虚IP:
http://192.168.7.70
返回如图：
证明，keepalived让haproxy1接管负载均衡，将页面跳转到apache2上
2.停掉haproxy1上的haproxy服务，5秒后keepalived会自动将其再次启动
（haproxy1）
# pkill haproxy
等5秒
# ps -ef |grep haproxy
--------------
root 1712 1708 0 01:17 ? 00:00:00 sh /etc/keepalived/check_haproxy.sh
haproxy 2440 1 0 01:29 ? 00:00:00 /usr/local/haproxy/sbin/haproxy -f
/usr/local/haproxy/haproxy.cfg
root 2443 1807 0 01:29 pts/1 00:00:00 grep haproxy
--------------
3.停掉主的keepalived，备机马上接管服务
（haproxy1）
# service keepalived stop
# uname -a
---------------
Linux ha1.example.com 2.6.32-279.el6.x86_64 #1 SMP Fri Jun 22 12:19:21 UTC 2012
x86_64 x86_64 x86_64 GNU/Linux
---------------
（haproxy2）
# ip add
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen
1000
link/ether 00:0c:29:ff:21:19 brd ff:ff:ff:ff:ff:ff
inet 192.168.7.72/24 brd 192.168.7.255 scope global eth0
inet 192.168.7.70/32 scope global eth0
inet6 fe80::20c:29ff:feff:2119/64 scope link
valid_lft forever preferred_lft forever
# uname -a
---------------
Linux ha2.example.com 2.6.32-279.el6.x86_64 #1 SMP Fri Jun 22 12:19:21 UTC 2012
x86_64 x86_64 x86_64 GNU/Linux
---------------
现已跳转到haproxy2,在浏览器再次访问该虚IP:
http://192.168.7.70
返回如图：
---------大功告成----------
