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）
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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;
}
}}
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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）：
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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
}
}
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备用节点的配置
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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
}
}
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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:
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 forever2: eth0:
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 forever137机器：
1: lo:
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 forever2: eth0:
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
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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
}
}
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备用节点的配置
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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
}}
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其中/home/jimite/keepalived/chk_nginx_pid.sh为
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#!/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。