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：

image

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