10.5. Keepalived实现基于Nginx的高可用

Keepalived是通过VRRP协议来实现高可用的，VRRP协议会将多台功能相同的路由器组成一个小组，这样小组里有1个master角色和N（N>=1）个backup角色。

master会通过组播的形式向各个backup发送VRRP协议的数据包，当backup收不到master发来的VRRP数据包时，就会认为master宕机了。此时就需要根据各个backup的优先级来决定谁成为新的master。

Keepalived有三个模块，分别是core、check和vrrp。其中，core模块是Keepalived的核心，负责主进程的启动、维护，以及全局配置文件的加载和解析；check模块负责健康检查；vrrp模块用来实现VRRP协议。

10.5.1. Nginx的master主机

master_keepalived.conf

global_defs {
   notification_email {
     aming@aminglinux.com
   }
   notification_email_from root@aminglinux.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}

vrrp_script chk_nginx {
    script "/usr/local/sbin/check_ng.sh"
    interval 3
}

vrrp_instance VI_1 {
    state MASTER
    interface ens33
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass aminglinux>com
    }
    virtual_ipaddress {
        192.168.188.100
    }

    track_script {
        chk_nginx
    }

}

master上检测脚本

check_ng.sh

#!/bin/bash
#时间变量，用于记录日志
d=`date --date today +%Y%m%d_%H:%M:%S`
#计算nginx进程数量
n=`ps -C nginx --no-heading|wc -l`
#如果进程为0，则启动nginx，并且再次检测nginx进程数量，
#如果还为0，说明nginx无法启动，此时需要关闭keepalived
if [ $n -eq "0" ]; then
        /etc/init.d/nginx start
        n2=`ps -C nginx --no-heading|wc -l`
        if [ $n2 -eq "0"  ]; then
                echo "$d nginx down,keepalived will stop" >> /var/log/check_ng.log
                systemctl stop keepalived
        fi
fi

10.5.2. Nginx的backup备机

backup_keepalived.conf

global_defs {
   notification_email {
     aming@aminglinux.com
   }
   notification_email_from root@aminglinux.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}

vrrp_script chk_nginx {
    script "/usr/local/sbin/check_ng.sh"
    interval 3
}

vrrp_instance VI_1 {
    state BACKUP
    interface ens33
    virtual_router_id 51
    priority 90
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass aminglinux>com
    }
    virtual_ipaddress {
        192.168.188.100
    }

    track_script {
        chk_nginx
    }

}

backup上的检测脚本

check_ng.sh

#时间变量，用于记录日志
d=`date --date today +%Y%m%d_%H:%M:%S`
#计算nginx进程数量
n=`ps -C nginx --no-heading|wc -l`
#如果进程为0，则启动nginx，并且再次检测nginx进程数量，
#如果还为0，说明nginx无法启动，此时需要关闭keepalived
if [ $n -eq "0" ]; then
        systemctl start nginx
        n2=`ps -C nginx --no-heading|wc -l`
        if [ $n2 -eq "0"  ]; then
                echo "$d nginx down,keepalived will stop" >> /var/log/check_ng.log
                systemctl stop keepalived
        fi
fi