这篇文章简单介绍利用keepalived软件，实现对nginx服务器的高可用，即实现故障自动切换。假设你已经安装好nginx，下面介绍keepalived的安装和使用。

keepalived安装

yum install openssl-devel
cd /tmp
wget http://www.keepalived.org/software/keepalived-1.2.2.tar.gz
tar xzf keepalived-1.2.2.tar.gz
cd keepalived-1.2.2
./configure
make && make install
cp /usr/local/etc/rc.d/init.d/keepalived /etc/init.d/
cp /usr/local/etc/sysconfig/keepalived /etc/sysconfig/
chmod +x /etc/init.d/keepalived
chkconfig --add keepalived
chkconfig keepalived on
mkdir /etc/keepalived
ln -s /usr/local/sbin/keepalived /usr/sbin/

keepalived的配置

更详细的keepalived配置文件说明可以执行man keepalived.conf查看。

我们假设主服务器IP:192.168.1.103,从服务器ip:192.168.1.101 虚拟ip:192.168.1.110

下面对主服务器的keepalived进行配置：

vi /etc/keepalived/keepalived.conf
global_defs {
   notification_email {
     admin@centos.bz
   }
   notification_email_from keepalived@domain.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}
vrrp_script chk_http_port {
                script "/opt/nginx_pid.sh"
                interval 2
                weight 2
}
vrrp_instance VI_1 {
    state MASTER        ############ 辅机为 BACKUP
    interface eth0
    virtual_router_id 51
    mcast_src_ip 192.168.1.103
    priority 102                  ########### 权值要比 back 高
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
track_script { 
        chk_http_port ### 执行监控的服务 
        }
    virtual_ipaddress {
       192.168.1.110
    }
}

从服务器：

global_defs {
   notification_email {
     admin@centos.bz
   }
   notification_email_from keepalived@domain.com
   smtp_server 127.0.0.1
   smtp_connect_timeout 30
   router_id LVS_DEVEL
}
vrrp_script chk_http_port {
                script "/opt/nginx_pid.sh"
                interval 2
                weight 2
}
vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 51
    mcast_src_ip 192.168.1.101
    priority 101              ##########权值 要比 master 低。。
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass 1111
    }
track_script { 
        chk_http_port ### 执行监控的服务 
        }
    virtual_ipaddress {
       192.168.1.110
    }
}

之后分别在主从服务器建立nginx的监控脚本：

vi /opt/nginx_pid.sh
#!/bin/bash
A=`ps -C nginx --no-header |wc -l`               
if [ $A -eq 0 ];then                                       
                /usr/local/nginx/sbin/nginx
                sleep 3
                if [ `ps -C nginx --no-header |wc -l` -eq 0 ];then
                       killall keepalived
                fi
fi

然后分别启动主从服务器的keepalived：

service keepalived start

keepalived的测试

我们在主服务器上执行命令ip a，显示如下：

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:aa:a1:e4 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.103/24 brd 255.255.255.255 scope global eth0
    inet 192.168.1.110/32 scope global eth0

证明主服务器已经绑定了虚拟ip 192.168.1.110

在从服务器上执行命令ip a,显示如下：

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:2b:94:3b brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.101/24 brd 255.255.255.255 scope global eth0

显示表明从服务器上没有绑定vip 192.168.1.110,只有本机真实ip192.168.1.101

下面我们停止主服务器的nginx进程，再看看ip绑定情况:

主服务器的情况：

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:aa:a1:e4 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.103/24 brd 255.255.255.255 scope global eth0

从服务器的情况：

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:0c:29:2b:94:3b brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.101/24 brd 255.255.255.255 scope global eth0
    inet 192.168.1.110/32 scope global eth0

由此可见vip已经指向了从服务器。