Keepalived服务 – Tech 学习之路

一、高可用

概念：多台业务系统提供相同的服务，如果其中一套业务系统故障，其他业务系统会自动接管业务；我们将其称为高可用；
目的：通常使用keepalived软件实现高可用，keepalived是借助VRRP(虚拟路由冗余协议)实现高可用功能；
应用场景：主要用于业务系统，保证业务系统的7x24小时运行；

二、VRRP

1.工作原理

2.角色

Master
Slave

通过结点设置的vrrp优先级选举主从关系；

3.模式

抢占式：高优先级结点恢复正常后，自动接管冗余结点业务
非抢占式：高优先级结点恢复正常后，不接管冗余结点业务，直到冗余结点发生故障；

三、Keepalived

1.配置文件

/etc/sysyconfig/keepalived keepalived服务启动参数配置文件
/etc/keepalived/keepalived.conf keepalived服务配置文件

2.工作原理

四、部署流程

step1 安装

yum install -y keepalived

[root@lb01 ~]# yum install -y keepalived
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
......
Dependencies Resolved

========================================================================================================
 Package                       Arch             Version                         Repository         Size
========================================================================================================
......
Installed:
  keepalived.x86_64 0:1.3.5-8.el7_6.5                                                                   

Dependency Installed:
  net-snmp-agent-libs.x86_64 1:5.7.2-38.el7_6.2         net-snmp-libs.x86_64 1:5.7.2-38.el7_6.2        

Complete!

step2 配置

vim/etc/keepalived/keepalived.conf

[抢占式]

Master(MASTER)配置

[root@lb01 /etc/keepalived]# vim keepalived.conf
global_defs {
   router_id LB01
}
vrrp_instance VI_1 {
    state MASTER                   #定义设备角色
    interface eth0                 #定义绑定接口
    virtual_router_id 51           #定义实例组ID
    priority 150                   #定义设备优先级
    advert_int 3                   #定义vrrp组播包宣告时间（3s）
    authentication {               #定义vrrp验证
        auth_type PASS
        auth_pass 1111
    }   
    virtual_ipaddress {            #定义vrrp虚拟IP地址
        10.0.0.13
    }

Slave(BACKUP)配置

[root@lb02 /etc/keepalived]# vim keepalived.conf
global_defs {
   router_id LB02
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 3
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.0.0.13
    }
}

[非抢占式]

官方建议：Keepalived设置为非抢占模式；避免业务频繁切换至不同的主机；
1、两个结点state都必须配置为BACKUP
2、两个结点都在vrrp instance中添加nopreempt参数
3、其中一个结点优先级必须高于另外一个结点

两台服务器都启用nopreempt后，必须修改角色状态统一为BACKUP，唯一的区分就是优先级

Master(BACKUP)配置

[root@lb01 /etc/keepalived]# vim /etc/keepalived/keepalived.conf
global_defs {
   router_id LB01
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    nopreempt             #开启非抢占模式
    priority 150
    advert_int 3
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.0.0.13
    }
}

Slave(BACKUP)配置

[root@lb02 /etc/keepalived]# vim keepalived.conf
global_defs {
   router_id LB02
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    priority 100
    nopreempt
    advert_int 3
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        10.0.0.13
    }
}

step3 启动

systemctl restart keepalived

[root@lb01 /etc/keepalived]# systemctl restart keepalived.service

step4 测试(非抢占式)

[root@lb01 /etc/keepalived]# systemctl restart keepalived.service

四、Keepalived与Nginx服务结合

Nginx负载均衡实现高可用，需要借助Keepalived地址漂移功能;

有Nginx负载均衡，并不一定必须要装Keepalived保证高可用；

1、判断Keepalived故障

故障原理

主备设备无法检测对端心跳，导致双方都判定自己是Master而互相抢占资源；

故障原因

服务器网线松动
服务器硬件故障或发生损坏现象崩溃
主备主机开启防火墙

解决思路

停止其中一台主机的Keepalived服务；

示例脚本

适用于抢占式-备机使用

[root@lb02 /etc/keepalived]# vim /server/scripts/keepalived_status.sh
#!/bin/bash
vip=10.0.0.13
master_ip=10.0.0.15
while true; do
    ping -c 2 -W 3 $master_ip &>/dev/null
    if [ $? -eq 0 -a `ip add|grep "$vip"|wc -l` -eq 1]；then
        echo "keepalived is Breakdown;"
    else
        echo "keepalived is OK!"
    fi
sleep5
done

2、判断Nginx故障

必要性

如果Nginx宕机，会导致用户请求失败，但是Keepalived并不会进行地址漂移