Net分散式系統之三：Keepalived+LVS+Nginx負載均衡之高可用

上一篇寫了nginx負載均衡，此篇實現高可用（HA）。系統整體設計是採用Nginx做負載均衡，若出現Nginx單機故障，則導致整個系統無法正常執行。針對系統架構設計的高可用要求，我們需要解決Nginx負載均衡出現單機故障時，系統正常執行的需求。所以系統架構引入Keepalived元件，實現系統高可用。

一、Keepalived介紹

Keepalived是分散式部署系統解決系統高可用的軟體，結合LVS（Linux Virtual Server）使用，其功能類似於heartbeat，解決單機當機的問題。

二、Keepalived技術原理

keepalived是以VRRP協議為實現基礎的，VRRP全稱Virtual Router Redundancy Protocol，即虛擬路由冗餘協議。通過VRRP協議結合LVS，對組群伺服器監控情況，若master出現當機情況，則將VIP漂移到backup機上。實現了分散式系統高可用。可以理解為：keepalived是LVS的管理軟體，根據監控情況，將當機伺服器從ipvsadm移除掉。

三、Keepalived+LVS+Nginx實現系統高可用

伺服器	IP地址	說明
虛擬IP	192.168.1.120:80
主機	192.168.1.104:80
備機	192.168.1.103:80
Web站點A	192.168.1.101:8081	不同埠
Web站點B	192.168.1.101:8082	不同埠

1、安裝ipvsadm，CentOS7自帶安裝包，通過yum進行安裝。實現系統支援LVS

yum install ipvsadm

1	yum install ipvsadm

2、安裝Keepalived軟體，並將keepalived設定開機啟動

yum install Keepalived

1	yum install Keepalived

systemctl enable keepalived

1	systemctl enable keepalived

3、進行Keepalived.conf配置，如果是MASTER機，將state BACKUP改為state MASTER。

vim /etc/keepalived/keepalived.conf
#配置的內容
! Configuration File for keepalived

global_defs {
   notification_email {
     xxx@126.com #收到通知的郵件地址
   }
   notification_email_from XX@126.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}

vrrp_script monitor_nginx{
   script "/usr/local/etc/keepalived/script/monitor_nginx.sh"
   interval 1
   weight -15
}

vrrp_instance VI_1 {
    state BACKUP 
    interface eno16777736 
    virtual_router_id 51
    priority 80
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.1.120
    }
    track_script {
        monitor_nginx
    }
}

virtual_server 192.168.1.120 80 {
    delay_loop 6
    lb_algo wrr 
    lb_kind DR
    persistence_timeout 50
    protocol TCP

    real_server 192.168.1.103 80 {
        weight 1
        TCP_CHECK {
            connect_timeout 10
            nb_get_retry 3
            delay_before_retry 3
            connect_port 80
        }
    }

    real_server 192.168.1.104 80 {
        weight 5
        TCP_CHECK {
            connect_timeout 10
            nb_get_retry 3
            delay_before_retry 3
            connect_port 80
        }
    }
}

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vim /etc/keepalived/keepalived.conf

#配置的內容

! Configuration File for keepalived

global_defs {

notification_email {

xxx@126.com #收到通知的郵件地址

}

notification_email_from XX@126.com

smtp_server 127.0.0.1

smtp_connect_timeout 30

router_id LVS_DEVEL

}

vrrp_script monitor_nginx{

script "/usr/local/etc/keepalived/script/monitor_nginx.sh"

interval 1

weight -15

}

vrrp_instance VI_1 {

state BACKUP

interface eno16777736

virtual_router_id 51

priority 80

advert_int 1

authentication {

auth_type PASS

auth_pass 1111

}

virtual_ipaddress {

192.168.1.120

}

track_script {

monitor_nginx

}

virtual_server 192.168.1.120 80 {

delay_loop 6

lb_algo wrr

lb_kind DR

persistence_timeout 50

protocol TCP

real_server 192.168.1.103 80 {

weight 1

TCP_CHECK {

connect_timeout 10

nb_get_retry 3

delay_before_retry 3

connect_port 80

}

real_server 192.168.1.104 80 {

weight 5

TCP_CHECK {

connect_timeout 10

nb_get_retry 3

delay_before_retry 3

connect_port 80

}

4、配置監控shell指令碼

（1）建立：vim /usr/local/etc/keepalived/script/monitor_nginx.sh（2）SHELL檔案內容#!/bin/bash  
if [ "$(ps -ef | grep "nginx: master process"| grep -v grep )" == "" ]
then  
    systemclt start nginx.service
    sleep 5    
  if [ "$(ps -ef | grep "nginx: master process"| grep -v grep )" == "" ]  
  then   
    killall keepalived  
  fi  
fi

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