用Keepalived搭建双Nginx server集群，防止单点故障

综述：

浏览器访问虚拟IP: 192.168.1.57, 该虚拟IP被Keepalived接管，两个Keepalived进程分别运行在物理IP为192.168.1.56和192.168.1.59服务器上，这两个服务器上都运行着Nginx server。Nginx server都监听虚拟IP 192.168.1.57. Nginx背后有一些web app集群，已经配置成upstream.

为了防止Nginx自己成为单点瓶颈，这里采用了双Nginx server的方式。每个Server都是Ubuntu 12.04. 

假定我的第一台Ubuntu server物理IP地址是192.168.1.56，已经安装了Nginx server，现在安装Keepalived，后面称这台为master server.

apt-get install keepalived

另外一台Ubuntu server物理IP是192.168.1.59, 也安装Nginx server和Keapalived. 后面称这台为backup server. Nginx的安装以及配置不是本文关注内容，请参考我的其他文章。

现在开始配置master server. 安装完成keepalived后，通过查看脚本/etc/init.d/keepalived里面发现，启动配置文件的路径是

CONFIG=/etc/keepalived/keepalived.conf

但是该文件现在还不存在。所以我创建一个，内容如下：

# Settings for notifications
global_defs {
    notification_email {
        csfreebird@gmail.com     # Email address for notifications
    }
    notification_email_from keepalived@your_company.com  # The from address for the notifications
    smtp_server 127.0.0.1
    smtp_connect_timeout 15
}

# Define the script used to check if haproxy is still working
vrrp_script chk_http_port {
    script "/etc/keepalived/check_nginx.sh" # check Nginx is alive or not
    interval 2 #
    weight 2
}


# Configuation for the virtual interface
vrrp_instance VI_1 {
    interface eth0
    state MASTER        # set this to BACKUP on the other machine
    priority 101        # set this to 100 on the other machine
    virtual_router_id 51

    smtp_alert          # Activate email notifications

    authentication {
    auth_type PASS
    auth_pass 1111      # Set this to some secret phrase
    }

    # The virtual ip address shared between the two loadbalancers
    virtual_ipaddress {
    192.168.1.57
    }

    # Use the script above to check if we should fail over
    track_script {
    chk_http_port
    }
}

说明：

1. smtp_server必须要用127.0.0.1

2. 自己要创建一个检查nginx进程的脚本

/etc/keepalived/check_nginx.sh

内容如下：

!/bin/bash

# try to start nginx if nginx process is dead
# shutdonw keepalived process if start nginx failed

pid=`ps -C nginx --no-header |wc -l`
if [ $pid -eq 0 ];then
    service nginx start
    sleep 3
    if [ `ps -C nginx --no-header |wc -l` -eq 0 ];then
        service keepalived stop
    fi
fi

3. 修改nginx的所有server配置，将server_name都改为虚拟IP

server_name  192.168.1.57;

4. 注意，这里的虚拟IP不是用修改/etc/network/interfaces的方式，而是在keepalived配置文件中直接设置，要想判断是否成功，直接ping 就行了，ifconfig是看不到的。

ping 192.168.1.57
PING 192.168.1.57 (192.168.1.57) 56(84) bytes of data.
64 bytes from 192.168.1.57: icmp_req=1 ttl=64 time=0.024 ms
64 bytes from 192.168.1.57: icmp_req=2 ttl=64 time=0.020 ms

对192.168.1.59做相同的配置，略有变化的是：

vrrp_instance VI_1 {
    interface eth0
    state BACKUP  // changed
    priority 100  // changed

通过轮流关闭master和backup，证明keepalived已经有效工作了。

参考资料：Keepalived官方文档真是够差的。

http://www.leaseweblabs.com/2011/09/setting-up-keepalived-on-ubuntu-load-balancing-using-haproxy-on-ubuntu-part-2/

http://blog.csdn.net/zmj_88888888/article/details/8825471