实验环境：
后端服务器：vm3 172.25.3.3、vm4172.25.3.4
haproxy主机: vm1 172.25.3.1、vm2 172.25.3.2
vm
首先在vm1、vm2上安装keepalived
注意：需要提前配置好高可用的yum仓库
vm1作为mastar，vm2作为backup

yum install keepalived -y

对vm1上的keepalived进行配置，使用外部脚本/opt/haproxy.sh：

[root@vm1 ~]# cat /opt/check_haproxy.sh 
#!/bin/bash
systemctl status haproxy &> /dev/null || systemctl restart haproxy &> /dev/null
killall -0 haproxy
if [ $? -ne 0 ];then
	systemctl stop keepalived
fi

脚本解释:首先使用 systemctl status haproxy查看haproxy服务的状态，如果服务状态正常（在运行中）不执行任何操作，如果服务没有正常运行，执行systemctl restar haproxy来启动haproxy服务。使用[ $? -ne 0 ]通过对执行结果的判断，如果执行成功，不做操作；如果执行失败，关闭keepalived，此时vip资源会迁移到备机（vm2）。

vm1上的keepalived配置文件：

! Configuration File for keepalived

global_defs {
     notification_email {
     root@localhost
   }
   notification_email_from keepalived
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
#vrrp_strict


   vrrp_garp_interval 0
   vrrp_gna_interval 0
}
##定义外部脚本
vrrp_script check_haproxy {
    script "/opt/check_haproxy.sh"
    interval 2
    weight 0
}

vrrp_instance VI_1 {
    state MASTER
   interface eth0
    virtual_router_id 56
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    track_script {
         check_haproxy
    }
    virtual_ipaddress {
        172.25.3.100
    }
}

vm2上的配置文件（有差异）

! Configuration File for keepalived

global_defs {
     notification_email {
     root@localhost
   }
   notification_email_from keepalived
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
#vrrp_strict


   vrrp_garp_interval 0
   vrrp_gna_interval 0
}
##定义外部脚本
vrrp_script check_haproxy {
    script "/opt/check_haproxy.sh"
    interval 2
    weight 0
}

vrrp_instance VI_1 {
    state BACKUP     //修改状态为backup
   interface eth0
    virtual_router_id 56
    priority 50    advert_int 1    //优先级修改为小于master的优先级
    
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    track_script {
         check_haproxy
    }
    virtual_ipaddress {
        172.25.3.100
    }
}

重启服务，这里我们用keepalived+haproxy实现了一个七层的负载均衡+高可用 。