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.
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[*]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
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[*]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：
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[*]# 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
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[*]/etc/keepalived/check_nginx.sh
内容如下：
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[*]!/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
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[*]server_name192.168.1.57;
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。
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[*]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：
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[*]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.iyunv.com/zmj_88888888/article/details/8825471
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