原理
一台nginx服务器在提供服务，另一台处于备用状态
基于心跳检测的故障转移机制
注意：备用机的配置要和主机保持一致，防止顶不住流量
安装
官网下载：https://www.keepalived.org/download.html
将下载的安装包上传到linux服务器，/home/software/下，并解压缩
进入并执行
./configure --prefix=/usr/local/keepalived --sysconf=/etc
make && make install
可通过 whereis keepalived 查看
安装位置：/usr/local/keepalived/sbin/keepalived
核心配置文件：/etc/keepalived/keepalived.conf
配置
进入到软件目录：/home/software/keepalived-version/keepalived/etc/
复制配置文件
cp init.d/keepalived /etc/init.d/
cp sysconfig/keepalived /etc/sysconfig/
使配置文件生效
systemctl daemon-reload
启动与停止
systemctl start keepalived.service
systemctl stop keepalived.service
systemctl restart keepalived.service
查看网卡：ip addr
进一步完善
上述配置只能实现当主机服务器宕机或者keepalived服务停止才会触发，此时与nginx无关<br><b>如要实现nginx宕机后，先尝试重启，重启几次后依然失败，再切换到备份机器则需写脚本</b>
在核心配置文件所在目录中新建脚本文件
vim check_nginx_alive_or_not.sh
chmod -x check_nginx_alive_or_not.sh
将该脚本与keepalived配置文件绑定，修改核心配置文件
systemctl restart keepalived.service
存在问题
资源浪费，备机可能永远得不到切换 ，白白浪费每年购买服务器的高额费用
解决方案：<b>keepalived 双主热备</b>
