Nginx+keepalive 負載均衡

1 規划和准備

兩台相同配置的web
用途	IP
MASTER	192.168.1.100
BACKUP	192.1681.101

2 安裝

兩台接入服務器分別安裝NginX和keepalived:

准備依賴包：

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

下載

wget http://nginx.org/download/nginx-1.2.4.tar.gz 
wget http://www.keepalived.org/software/keepalived-1.2.7.tar.gz

安裝NginX

安裝keepalive

tar zxvf keepalived-1.2.7.tar.gz
cd keepalived-1.2.7
./configure
make 
make install

cp /usr/local/etc/rc.d/init.d/keepalived /etc/rc.d/init.d/
cp /usr/local/etc/sysconfig/keepalived /etc/sysconfig/
mkdir /etc/keepalived
cp /usr/local/etc/keepalived/keepalived.conf /etc/keepalived/
cp /usr/local/sbin/keepalived /usr/sbin/

加入啟動服務

echo "/usr/local/nginx/sbin/nginx" >> /etc/rc.local
echo "/etc/init.d/keepalived start" >> /etc/rc.local

3  配置

3.1 配置NginX

　　兩台接入服務器的NginX的配置完全一樣,主要是配置/usr/local/nginx/conf/nginx.conf的http。其中多域名指向是通過虛擬主機（配置http下面的server）實現；同一域名的不同虛擬目錄通過每個server下面的不同location實現；到后端的服務器在http下面配置upstream,然后在server或location中通過proxypass引用。要實現前面規划的接入方式，http的配置如下：

http {
    include       mime.types;
    default_type  application/octet-stream;

    sendfile        on;

    upstream dev.hysec.com {
        server 50.1.1.21:80;
    }


    upstream opslinux.com {
      ip_hash;
      server 192.168.1.102:80
      server 192.168.1.103:80
      server 192.168.1.104:80
    }
    server {
        listen       80;
        server_name  opslinux.com;
        location / {
            proxy_pass http://opslinux.com;
        }
}

驗證方法：

首先用IP訪問前表中各個應用服務器的url

再用域名和路徑訪問前表中各個應用系統的域名/虛擬路徑

3.2 配置keepalived

按照上面的安裝方法，keepalived的配置文件在/etc/keepalived/keepalived.conf。主、從服務器的配置相關聯但有所不同。如下：

Master:

! Configuration File for keepalived

global_defs {
  router_id NGINX_DEVEL
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 101
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
       192.168.1.100
    }
}

Backup:

! Configuration File for keepalived

global_defs {
  router_id NGINX_DEVEL
}

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 {
       192.168.1.100
    }
}

驗證：

先后在主、從服務器上啟動keepalived: /etc/init.d/keepalived start

在主服務器上查看是否已經綁定了虛擬IP： ip addr

停止主服務器上的keepalived: /etc/init.d/keepalived stop 然后在從服務器上查看是否已經綁定了虛擬IP：

啟動主服務器上的keepalived，看看主服務器能否重新接管虛擬IP

3.3 讓keepalived監控NginX的狀態

經過前面的配置，如果主服務器的keepalived停止服務，從服務器會自動接管VIP對外服務；一旦主服務器的keepalived恢復，會重新接管VIP。 但這並不是我們需要的，我們需要的是當NginX停止服務的時候能夠自動切換。

keepalived支持配置監控腳本，我們可以通過腳本監控NginX的狀態，如果狀態不正常則進行一系列的操作，最終仍不能恢復NginX則殺掉keepalived，使得從服務器能夠接管服務。

如何監控NginX的狀態

最簡單的做法是監控NginX進程，更靠譜的做法是檢查NginX端口，最靠譜的做法是檢查多個url能否獲取到頁面。

如何嘗試恢復服務

如果發現NginX不正常，重啟之。等待3秒再次校驗，仍然失敗則不再嘗試。

根據上述策略很容易寫出監控腳本。這里使用nmap檢查nginx端口來判斷nginx的狀態，記得要首先安裝nmap。監控腳本如下:

#!/bin/bash
# check nginx server status
NGINX=/usr/local/nginx/sbin/nginx
PORT=8080

nmap localhost -p $PORT | grep "$PORT/tcp open"
#echo $?
if [ $? -ne 0 ];then
    $NGINX -s stop
    $NGINX
    sleep 3
    nmap localhost -p $PORT | grep "$PORT/tcp open"
    [ $? -ne 0 ] && /etc/init.d/keepalived stop
fi

不要忘了設置腳本的執行權限，否則不起作用。

假設上述腳本放在/opt/chk_nginx.sh，則keepalived.conf中增加如下配置：

主keepalived
vrrp_script chk_http_port {
    script "/opt/chk_nginx.sh"
    interval 1
    weight -2
}

track_script {
    chk_http_port
}


例子：
! Configuration File for keepalived

global_defs {
   router_id NGINX_UPSTEAM
}

vrrp_script chk_http_port {
    script "/opt/chk_nginx.sh"
    interval 1
    weight -2
}

vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 51
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    virtual_ipaddress {
        192.168.1.100
    }

    track_script {
    chk_http_port
    }

}

更進一步，為了避免啟動keepalived之前沒有啟動nginx , 可以在/etc/init.d/keepalived的start中首先啟動nginx:

start() {
    /usr/local/nginx/sbin/nginx
    sleep 3
    echo -n $"Starting $prog: "
    daemon keepalived ${KEEPALIVED_OPTIONS}
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && touch /var/lock/subsys/$prog
}