这里我们仅仅只利用Keepalived做双机热备，也就是保证服务器的高可用性，其他的不用管。
一、Keepalived双机热备的应用场景
二、Keepalived双机热备的特性以及优缺点
特性：
1，至少需要两台服务器，其中一台为master始终提供服务，另外一台作为backup始终处于空闲状态，只有在主服务器挂掉的时候他就来帮忙了，这是典型的双机热备
2，能根据需求判断服务是否可用，在不可用的时候要即使切换 优缺点：
优点：数据同步非常简单，不像负载均衡对数据一致性要求非常高，实现起来相对复杂维护也颇为不便，双机热备用rsync就可以实现了操作和维护非常简单
缺点：服务器有点浪费，始终有一台处于空闲状态
三、Keepalived双机热备的配置
首先画个双机热备拓扑图吧：
Keepalived安装
操作系统：Linux6.3 2.6.32
下载软件
keepalived官方地址：http://www.keepalived.org/download.html
大家可以到这里下载最新版本的keepalived（如果已经提供用提供的安装包keepalived-1.2.15.tar.gz）
创建目录、压缩文件上传、解压（主备机进行相同操作）
mkdir -p /usr/local/HAsoft
cd /usr/local/HAsoft
tar -zxvf keepalived-1.2.15.tar.gz
cd keepalived-1.2.15
预编译
./configure --prefix=/usr/local/keepalived --with-kernel-dir=/usr/src/kernels/2.6.32-279.el6.x86_64/
（kernels后面的版本“2.6.32-279.el6.x86_64”以实际安装linux版本为准，不要复制直接按Tab键自动补全即可） 结果如下：（出现如下类似结果就行）
Keepalived configuration
------------------------
Keepalived version : 1.2.15
Compiler : gcc
Compiler flags : -g -O2 -DETHERTYPE_IPV6=0x86dd
Extra Lib : -lssl -lcrypto -lcryptUse IPVS Framework : Yes
IPVS sync daemon support : Yes
IPVS use libnl : No
Use VRRP Framework : Yes
Use Debug flags : No
编译
make && make install
整理管理文件：
cp /usr/local/keepalived/sbin/keepalived /usr/sbin/
cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
cp /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/
建立配置文件目录
mkdir -p /etc/keepalived/
注意：keepalived的配置文件默认在/etc/keepalived/目录 两台服务器(两个节点)都这样安装即可
配置 打开配置文件：（该文件不存在，需手动创建）
vim /etc/keepalived/keepalived.conf
按i键将下面主机配置的内容复制粘贴到keepalived.conf中，并按时间环境修改标红的配置项。
主机配置
global_defs
{
}
vrrp_instance N1 { //定义一个vrrp组
state MASTER //指定哪个为master（主机），哪个为backup（备机）。
mcast_src_ip 192.166.66.80 //此处ip填写本机ip即可（非必要设置）
interface eth2 //设置实例绑定的网卡
virtual_router_id 51 // VPID标记 (主机备机要一致)
priority 100 //定义优先级，数字越大，优先级越高
authentication { //验证类型和密码
auth_type PASS
auth_pass 123456
}
virtual_ipaddress { //虚拟IP
192.166.66.85
}
}
备机配置
vim /etc/keepalived/keepalived.conf
将下面内容复制到keepalived.cong中，并按实际环境修改标红配置项。
global_defs
{
}
vrrp_instance N1 {
state BACKUP
interface eth2
mcast_src_ip 192.166.66.81
virtual_router_id 51
priority 88
authentication {
auth_type PASS
auth_pass 123456
}
virtual_ipaddress {
192.166.66.85
}
}
四、启动调试
在节点A即主机上启动keepalive
/etc/init.d/keepalived start
启动日志：（/var/log/message）
tail -f /var/log/messages
Sep 8 18:26:02 centosaKeepalived_vrrp: Registering Kernel netlink reflector
Sep 8 18:26:02 centosaKeepalived_vrrp: Registering Kernel netlink command channel
Sep 8 18:26:02 centosaKeepalived_vrrp: Registering gratutious ARP shared channel
Sep 8 18:26:02 centosaKeepalived_vrrp: Opening file '/etc/keepalived/keepalived.conf'.
Sep 8 18:26:02 centosaKeepalived_vrrp: Configuration is using : 36076 Bytes
Sep 8 18:26:02 centosaKeepalived_vrrp: Using LinkWatch kernel netlink reflector...
Sep 8 18:26:02 centosa Keepalived: Starting VRRP child process, pid=5606
Sep 8 18:26:07 centosaKeepalived_vrrp: VRRP_Instance(lnmp) Transition to MASTER STATE
Sep 8 18:26:12 centosaKeepalived_vrrp: VRRP_Instance(lnmp) Entering MASTER STATE
Sep 8 18:26:12 centosaavahi-daemon[2528]: Registering new address record for 192.168.17.200 on eth0.
在节点B即备机上上启动
/etc/init.d/keepalived start
启动日志：
tail -f /var/log/messages
Sep 8 18:30:02 centosb Keepalived: Starting Keepalived v1.2.2 (09/08,2011)
Sep 8 18:30:02 centosb Keepalived: Starting Healthcheck child process, pid=5837
Sep 8 18:30:02 centosbKeepalived_vrrp: Registering Kernel netlink reflector
Sep 8 18:30:02 centosbKeepalived_vrrp: Registering Kernel netlink command channel
Sep 8 18:30:02 centosbKeepalived_vrrp: Registering gratutious ARP shared channel
Sep 8 18:30:02 centosb Keepalived: Starting VRRP child process, pid=5839
Sep 8 18:30:02 centosb kernel: IPVS: Registered protocols (TCP, UDP, AH, ESP)
Sep 8 18:30:02 centosb kernel: IPVS: Connection hash table configured (size=4096, memory=32Kbytes)
Sep 8 18:30:02 centosb kernel: IPVS: ipvs loaded.
Sep 8 18:30:02 centosbKeepalived_healthcheckers: Registering Kernel netlink reflector
Sep 8 18:30:02 centosbKeepalived_healthcheckers: Registering Kernel netlink command channel
Sep 8 18:30:02 centosbKeepalived_healthcheckers: Opening file '/etc/keepalived/keepalived.conf'.
Sep 8 18:30:02 centosbKeepalived_vrrp: Opening file '/etc/keepalived/keepalived.conf'.
Sep 8 18:30:02 centosbKeepalived_vrrp: Configuration is using : 36252 Bytes
Sep 8 18:30:02 centosbKeepalived_vrrp: Using LinkWatch kernel netlink reflector...
Sep 8 18:30:02 centosbKeepalived_healthcheckers: Configuration is using : 6271 Bytes
Sep 8 18:30:02 centosbKeepalived_healthcheckers: Using LinkWatch kernel netlink reflector...
Sep 8 18:30:02 centosbKeepalived_vrrp: VRRP_Instance(lnmp) Entering BACKUP STATE
从日志可以看出，启动都没有问题，并且安装我给的优先级完成了竞选，各自成就了各自的状态
在本机运行cmd命令 Ping 192.168.17.200 看能否正常ping通。
关闭节点A主机的服务测试切换是否正常
/etc/init.d/keepalived stop
观察节点B的日志：
Sep 8 18:32:55 centosbKeepalived_vrrp: VRRP_Instance(lnmp) Transition to MASTER STATE
Sep 8 18:33:00 centosbKeepalived_vrrp: VRRP_Instance(lnmp) Entering MASTER STATE
Sep 8 18:33:00 centosbavahi-daemon[2531]: Registering new address record for 192.168.17.200 on eth0.
在本机运行cmd命令 Ping 192.168.17.200 看能否正常ping通。
启动节点A的服务测试切换是否正常
/etc/init.d/keepalived start
观察节点B的日志：
Sep 8 18:33:31 centosbKeepalived_vrrp: VRRP_Instance(lnmp) Received higher prio advert
Sep 8 18:33:31 centosbKeepalived_vrrp: VRRP_Instance(lnmp) Entering BACKUP STATE
Sep 8 18:33:31 centosbavahi-daemon[2531]: Withdrawing address record for 192.168.17.200 on eth0.
在本机运行cmd命令 Ping 192.168.17.200 看能否正常ping通。
注意把keepalived写在开机启动里面 准备机同时设置
vim /etc/rc.local
输入下面内容保存
service keepalived start