双机热备是指两台机器都在运行，但并非两台机器同时在提供服务。 当提供服务的一台出现故障的时候，另外一台会马上自动接管并且提供服务，且切换的时间非常短。

keepalived的工作原理是VRRP——虚拟路由冗余协议。

测试环境如下：

ip

vip

master

192.168.174.135

192.168.174.140

backup

192.168.174.137

192.168.174.140

回到顶部 nginx 安装

sudo apt-get install nginx 查找配置文件位置

sudo find / -name nginx.conf /etc/nginx/nginx.conf 修改配置文件（nginx.conf）

复制代码 user www-data; worker_processes 4; pid /run/nginx.pid;

events { worker_connections 1024; }

http { sendfile on; tcp_nopush on; tcp_nodelay on; keepalive_timeout 65; types_hash_max_size 2048;

include /etc/nginx/mime.types;
default_type application/octet-stream;

access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;

server {
    listen 80 default_server;
    server_name test;
    charset utf-8;

    location / {
    root html;
    index index.html index.htm;
    proxy_set_header X-Real_IP $remote_addr;
    client_max_body_size 100m;
    }
}

} 复制代码 文件/usr/share/nginx/html/index.html

在192.168.174.135上加上 Welcome to nginx! 135

在192.168.174.137上加上 Welcome to nginx! 137

启动

sudo service nginx start
关闭

sudo service nginx stop 回到顶部 keepalived 安装

下载keepalived-1.2.19.tar.gz

tar –zxvf keepalived-1.2.19.tar.gz cd keepalived-1.2.19 ./configure --prefix=/usr/local/keepalived make sudo make install 期间可能出现问题：

!!! OpenSSL is not properly installed on your system. !!! !!! Can not include OpenSSL headers files. !!!

解决

sudo apt-get install libssl.dev 建立软链接

sudo ln -s /usr/local/keepalived/sbin/keepalived /sbin/ sudo ln -s /usr/local/keepalived/etc/rc.d/init.d/keepalived /etc/init.d/ sudo ln -s /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/ 启动

sudo keepalived -D -f /usr/local/keepalived/etc/keepalived/keepalived.conf 关闭

sudo killall keepalived 配置（keepalived.conf）：

复制代码 global_defs { router_id NODEA }

vrrp_instance VI_1 { state MASTER interface eth0 #监测网络接口 virtual_router_id 50 #主、备必须一样
priority 100 #优先级：主＞备 advert_int 1 authentication { auth_type PASS #VRRP认证，主备一致 auth_pass 1111 #密码 }

virtual_ipaddress { 192.168.174.140/24 #VRRP HA虚拟地址 } } 复制代码 备用节点的配置

复制代码 global_defs { router_id NODEB }

vrrp_instance VI_1 { state BACKUP interface eth0 virtual_router_id 50 priority 90 advert_int 1 authentication { auth_type PASS auth_pass 1111 }

virtual_ipaddress { 192.168.174.140/24 } } 复制代码 回到顶部 测试 双击热备

两台机子均启动nginx和keepalived，浏览器各自访问

浏览器访问：http://192.168.174.140/，显示的是MASTER的页面。

同样用ip appr可以验证：

135机器：

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

   valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

   valid_lft forever preferred_lft forever

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:39:d4:88 brd ff:ff:ff:ff:ff:ff

inet 192.168.174.135/24 brd 192.168.174.255 scope global eth0

   valid_lft forever preferred_lft forever

inet 192.168.174.140/24 scope global secondary eth0

   valid_lft forever preferred_lft forever

inet6 fe80::20c:29ff:fe39:d488/64 scope link

   valid_lft forever preferred_lft forever

137机器：

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

   valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

   valid_lft forever preferred_lft forever

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000

link/ether 00:0c:29:cf:23:62 brd ff:ff:ff:ff:ff:ff

inet 192.168.174.137/24 brd 192.168.174.255 scope global eth0

   valid_lft forever preferred_lft forever

inet6 fe80::20c:29ff:fecf:2362/64 scope link

   valid_lft forever preferred_lft forever

现在关闭135机器的keepalived。

但当nginx宕掉或整个机子宕机后，这种情况不行了——通过浏览器访问192.168.174.140访问不到资源。

nginx宕掉/机器宕掉热备

为了解决上一问题，可以利用脚本，当检测到nginx进程宕掉后，自动关闭keepalived进程，从而实现热备份。

主节点的配置

复制代码 global_defs { router_id NODEA }

vrrp_script chk_http_port { script "/home/jimite/keepalived/chk_nginx_pid.sh" interval 2 weight 2 }

vrrp_instance VI_1 { state MASTER interface eth0 virtual_router_id 50 priority 100 advert_int 1 authentication { auth_type PASS auth_pass 1111 } track_script { chk_http_port } virtual_ipaddress { 192.168.174.140/24 } } 复制代码 备用节点的配置

复制代码 global_defs { router_id NODEB }

vrrp_script chk_http_port { script "/home/jihite/keepalived/chk_nginx_pid.sh" interval 2 weight 2 }

vrrp_instance VI_1 { state BACKUP interface eth0 virtual_router_id 50 priority 90 advert_int 1 authentication { auth_type PASS auth_pass 1111 } track_script { chk_http_port }

virtual_ipaddress {
192.168.174.140/24
}

} 复制代码 其中/home/jimite/keepalived/chk_nginx_pid.sh为

复制代码 #!/bin/bash A=ps -C nginx --no-header |wc -l if [ $A -eq 0 ] then echo 'nginx server is died' sudo killall keepalived fi 问题：杀死keepalived进程后，可以实现vip的偏移，但是原机器的vip无法自动删除 原因：VRRP协议原理是：只有MASTER对外发送消息。各BACKUP接受消息，当接受不到消息时会在剩下的BACKUP机器中选出新的MASTER。 之前用kill -9 pid 或killall pid杀死keepalived进程，导致安装keepalived不能发送信息，BACKUP收不到信息升级为MASTER，但是由于进程被杀死【非正常关闭】，导致keepalived没有能力自己删除vip。 解决方案：关闭keepalived时用命令 service keepalived stop 或 kill -15 pid（注：只删除第一个进程号） 存在问题： 非正常关闭keepalived。 禁止使用kill -9 或killall杀死keepalived。