1、问题

SQL 错误 [08S01]: Communications link failure

The last packet successfully received from the server was 665,722 milliseconds ago. The last packet sent successfully to the server was 665,758 milliseconds ago.
  Communications link failure

The last packet successfully received from the server was 665,722 milliseconds ago. The last packet sent successfully to the server was 665,758 milliseconds ago.
  Communications link failure

The last packet successfully received from the server was 665,722 milliseconds ago. The last packet sent successfully to the server was 665,758 milliseconds ago.
    Socket is closed
    Socket is closed

2、场景

测试接口时外网数据库突然连接不上。

3、原因

===待梳理=

4、解决方案

ping 一下 MySQL 所在主机的 IP，果然没有 ping 通。

查询到的方案如下：

第一种：MySQL数据服务没有开启导致连接失败

第二种：MySQL数据库设置成了外网不能访问，需要开启外网IP访问的功能。

第三种：可能是网络问题，导致连接不上，ping 一下 MySQL 所在主机的 IP

第四种：数据设置wait_timeout时间，在默认配置不改变的情况下，如果连续8小时内都没有访问数据库的操作，再次访问mysql数据库的时候，mysql数据库会拒绝访问。

参考文章