什么是高可用

一般是指2台机器启动着完全相同的业务系统，当有一台机器down机了，另外一台服务器就能快速的接管，对于访问的用户是无感知的。

高可用通常使用什么软件？

硬件通常使用 F5软件通常使用 keepalived

keepalived是如何实现高可用的？

keepalived软件是基于VRRP协议实现的，VRRP虚拟路由冗余协议，主要用于解决单点故障问题

Keepalived高可用安装配置 {#p-2}

|------| | 环境准备 |

|--------------| | 安装keepalived |

[root@lb01 ~]# yum install -y keepalived
[root@lb02 ~]# yum install -y keepalived

1-配置master

#找到配置文件
[root@lb02 ~]# rpm -qc keepalived
/etc/keepalived/keepalived.conf
/etc/sysconfig/keepalived

#编辑配置文件
[root@lb01 ~]# cat /etc/keepalived/keepalived.conf
global_defs {                   #全局配置
    router_id lb01              #标识身份->名称
}

vrrp_instance VI_1 {
    state MASTER                #标识角色状态
    interface eth0              #网卡绑定接口
    virtual_router_id 50        #虚拟路由id
    priority 150                #优先级
    advert_int 1                #监测间隔时间
    authentication {            #认证
        auth_type PASS          #认证方式
        auth_pass 1111          #认证密码
    }
    virtual_ipaddress {         
        10.0.0.3                #虚拟的VIP地址
    }
}

209上的配置：

global_defs {
    router_id lb01
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 50
    priority 150
    unicast_src_ip 192.168.1.209 #本机ip
    unicast_peer {
    192.168.1.210 #对端ip
    }
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {         
        192.168.1.200
    }
}

2- 配置 BACKUP

[root@lb02 ~]# cat /etc/keepalived/keepalived.conf


global_defs {
    router_id lb02
}

vrrp_instance VI_1 {
    state BACKUP        
    interface eth0
    virtual_router_id 50
    priority 100
    unicast_src_ip 192.168.1.210 #本机ip
    unicast_peer {
    	192.168.1.209 #对端ip
    }


    advert_int 1
    authentication {    
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.1.200
    }
}

对比master与Backup的keepalived配置区别

| Keepalived配置区别 | Master节点配置 | Backup节点配置 | |-----------------|----------------|----------------| | route_id（唯一标识） | router_id lb01 | router_id lb02 | | state（角色状态） | state MASTER | state BACKUP | | priority(竞选优先级) | priority 150 | priority 100 |

启动Master和Backup节点的keepalived
#Master节点
[root@lb01 ~]# systemctl start keepalived
[root@lb01 ~]# systemctl enable keepalived

#Backup节点
[root@lb02 ~]# systemctl start keepalived
[root@lb02 ~]# systemctl enable keepalived

验证：

ip a 

systemctl status keepalived.service

209：in MASTER adver

210：Entering BACKUP STATE

出现双vip 解决方法

keepalived两台机器同时出现vip问题 - linhaifeng - 博客园 (cnblogs.com)

检查网卡 上的 流量：

tcpdump -i eth0 vrrp -n

210：

{#more-7995}

配置keealived检测nginx脚本

1.脚本内容:

cat check_web.sh

#!/bin/sh
nginxpid=$(ps -C nginx --no-header|wc -l)

#1.判断Nginx是否存活,如果不存活则尝试启动Nginx
if [ $nginxpid -eq 0 ];then
    systemctl start nginx &>/dev/null
    sleep 2
    #2.等待2秒后再次获取一次Nginx状态
    nginxpid=$(ps -C nginx --no-header|wc -l) 
    #3.再次进行判断, 如Nginx还不存活则停止Keepalived,让地址进行漂移,并退出脚本  
    if [ $nginxpid -eq 0 ];then
        systemctl stop keepalived
   fi
fi

给脚本执行权限、

chmod +x check_web.sh

2.脚本集成到keepalived软件

[root@lb01 ~]# cat /etc/keepalived/keepalived.conf

global_defs {
    router_id lb01
}

#定义脚本
vrrp_script check_web {
    script "/root/check_web.sh"
    interval 4
}


vrrp_instance VI_1 {
    state MASTER
   #nopreempt
    interface eth0
    virtual_router_id 50
    priority 150
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {         
        10.0.0.3
    }
    # 调用脚本
    track_script {
       check_web
    }
}