Redis主从自动failover
Redis主从架构持久化存在一个问题，即前次测试的结论，持久化需要配置在主实例上才能跨越实例保证数据不丢失，这样以来主实例在持久化数据到硬盘的过程中，势必
Redis主从架构持久化存在一个问题，即前次测试的结论，持久化需要配置在主实例上才能跨越实例保证数据不丢失，这样以来主实例在持久化数据到硬盘的过程中，势必会造成磁盘的I/O等待，香港虚拟主机，经过实际测试，这个持久化写硬盘的过程给应用程序带来的影响无法忍受；因而在大多数场景下，会考虑把持久化配置在从实例上，当主实例宕机后，通过手动或者自动的方式将从实例提升为主实例，继续提供服务！当主实例恢复后，先从原从实例上同步数据，同步完成后再恢复到原始的主从状态！要实现这种的要求，需要有keepalive的配合，一方面keepalive提供了VIP，可以避免修改应用程序连接，同时redis实例的配置文件监听部分也需要修改为全网监听；另一方面keepalive定时调度脚本来监控主从实例的状态，香港服务器，根据具体情况进行切换！本文将重点介绍下使用keepalive实现redis主从自动failover！
环境介绍
操作系统版本均为：rhel5.4 64bit
redis版本：2.6.4
redis实例端口均为：6379
redis实例密码均为：123
VIP：192.168.1.120
主实例为server11(192.168.1.112)
从实例为server12(192.168.1.113，开启快照持久化)
一：安装keepalive软件,server11安装完成后直接scp至server12上即可
二：配置主节点server11配置文件
三：配置从节点server12配置文件
四：准备相关的脚本，主从实例上都需要存在这些脚本，同时注意脚本需要由可执行权限
五：主从实例分别启动keepalive进程，测试VIP是否正常(这里就要修改redis配置文件的监听地址为0.0.0.0)
六：主实例写入测试数据，该脚本原则上会写入25条测试数据，不过由于未优化redis默认并发数，会导致一些写入请求失败，最终功写入231839条测试数据，占内存总大小为25M左右，写入过程中可以观察主从实例的持久化文件变化情况，网站空间，主实例的持久化文件维持在30k，从实例的则不断的扩展！
七：模拟主实例故障，观察日志输出，验证从实例是否能成功接管VIP，同时将实例变成读写模式
八：继续使用脚本写入测试数据，通过重复运行脚本更新记录，这次成功写入了249925条测试数据
九:主实例角色的恢复过程，使用shell脚本自动恢复
十：验证数据完整性和主从角色恢复情况
参考文档：
本文出自 “斩月” 博客，谢绝转载！
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