實際工作中ngnix肯定要做成高可用模式，防止一個ngnix掛了，所有請求都無法訪問成功，我們可以利用keepalived實現高可靠來動態管理ngnix,cong從而讓ngnix也具備高可用性。

1 ，keepalived實現高可靠（HA）

HA(High Available), 高可用性叢集，是保證業務連續性的有效解決方案，一般有兩個或兩個以上的節點，且分為活動節點及備用節點，keepalive是一款可以實現高可靠的軟體，通常部署在2臺伺服器上，分為一主一備。Keepalived可以對本機上的程序進行檢測，一旦Master檢測出某個程序出現問題，將自己切換成Backup狀態，然後通知另外一個節點切換成Master狀態。

2，keepalived安裝

下載keepalived官網:http://keepalived.org

將keepalived解壓到/usr/app目錄下

tar -zxvf  keepalived-1.2.19.tar.gz -C /usr/app/

進入到/usr/app/keepalived-1.2.19目錄

cd /usr/app/keepalived-1.2.19

開始configure

./configure --prefix=/usr/app/keepalived                             #指定keepalived的目錄為 /usr/app/keepalived  

如果安裝報錯，是因為少一些依賴，執行如下命令安裝依賴大全，，，

yum -y install gcc pcre-devel openssl openssl-devel

#編譯並安裝

make && make install

3，將keepalived新增到系統服務中

拷貝執行檔案

cp /usr/app/keepalived/sbin/keepalived /usr/sbin/

將init.d檔案拷貝到etc下,加入開機啟動項

cp /usr/app/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/keepalived

將keepalived檔案拷貝到etc下

cp /usr/app/keepalived/etc/sysconfig/keepalived /etc/sysconfig/

建立keepalived資料夾

mkdir -p /etc/keepalived

將keepalived配置檔案拷貝到etc下

cp /usr/app/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf

新增可執行許可權

chmod +x /etc/init.d/keepalived

新增keepalived到開機啟動

chkconfig --add keepalived     

chkconfig keepalived on

4, 配置keepalived虛擬IP

修改配置檔案： /etc/keepalived/keepalived.conf

#MASTER節點

global_defs {
}
vrrp_instance VI_1 {
    state MASTER   #指定A節點為主節點 備用節點上設定為BACKUP即可
    interface eth0    #繫結虛擬IP的網路介面
    virtual_router_id 51   #VRRP組名，兩個節點的設定必須一樣，以指明各個節點屬於同一VRRP組
    priority 100   #主節點的優先順序（1-254之間），備用節點必須比主節點優先順序低
    advert_int 1  #組播資訊傳送間隔，兩個節點設定必須一樣
    authentication {    #設定驗證資訊，兩個節點必須一致
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {    #指定虛擬IP, 兩個節點設定必須一樣
        192.168.33.60/24    #如果兩個nginx的ip分別是192.168.33.61,,...62，則此處的虛擬ip跟它倆同一個網段即可
    }
}

#BACKUP節點

global_defs {
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    priority 99
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.33.60/24
    }
}

#分別啟動兩臺機器上的keepalived

service keepalived start

測試：

殺掉master上的keepalived程序，你會發現，在slave機器上的eth0網絡卡多了一個ip地址

檢視ip地址的命令：  ip addr

其實他的原理就是根據兩臺keepalived伺服器繫結的共同的網段的ip地址（192.168.33.60），利用這個ip實現主備跳轉切換，訪問該ip預設等於訪問主機的實際ip，當主機掛了，備機自動切換為主機，這是使用該ip訪問依然成功，不過就相當於訪問了備機ip。

5，配置keepalived心跳檢查

要想實現ngnix主備自動切換，需要讓使用者自定義一個shell指令碼並利用keepalived去檢測使用者自己的程式，返回狀態給keepalived就可以了, 當指令碼檢測到 test1 伺服器上的 ngnix掛了，那麼keepalived會自動切換為test2伺服器上的keepalived, 同時test1上的keepalived會根據自定義編寫的指令碼對test1上的ngnix進行重啟或關閉等操作。

修改配置檔案： /etc/keepalived/keepalived.conf

#MASTER節點

global_defs {
}

vrrp_script chk_health {
    script "[[ `ps -ef | grep nginx | grep -v grep | wc -l` -ge 2 ]] && exit 0 || exit 1"
    interval 1    #每隔1秒執行上述的指令碼，去檢查使用者的程式ngnix
    weight -2
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 1
    priority 100
    advert_int 2
    authentication {
        auth_type PASS
        auth_pass 1111
    }

    track_script {
        chk_health
    }

    virtual_ipaddress {
        10.0.0.10/24
    }

    notify_master "/usr/local/keepalived/sbin/notify.sh master"
    notify_backup "/usr/local/keepalived/sbin/notify.sh backup"
    notify_fault "/usr/local/keepalived/sbin/notify.sh fault"
}

#BACKUP節點

global_defs {
}

vrrp_script chk_health {
    script "[[ `ps -ef | grep nginx | grep -v grep | wc -l` -ge 2 ]] && exit 0 || exit 1"
    interval 1
    weight -2
}

vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 1
    priority 99
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }

    track_script {
        chk_health
    }

    virtual_ipaddress {
        10.0.0.10/24
    }
	
    notify_master "/usr/local/keepalived/sbin/notify.sh master"
    notify_backup "/usr/local/keepalived/sbin/notify.sh backup"
    notify_fault "/usr/local/keepalived/sbin/notify.sh fault"
}

#新增切換通知指令碼

vi /usr/app/keepalived/sbin/notify.sh

#!/bin/bash

case "$1" in
    master)
        /usr/local/nginx/sbin/nginx
        exit 0
    ;;
backup)
        /usr/local/nginx/sbin/nginx -s stop
        /usr/local/nginx/sbin/nginx
        exit 0
    ;;
    fault)
        /usr/local/nginx/sbin/nginx -s stop
        exit 0
    ;;
    *)
        echo 'Usage: notify.sh {master|backup|fault}'
        exit 1
    ;;
esac

#在第二臺機器上新增notify.sh指令碼

#分別在兩臺機器上啟動keepalived

service keepalived start

chkconfig keepalived on

接下來自行測試即可，手動殺死ngnix程序，檢視主備變化，自己看不解釋了。