Docker镜像拉取失败或超时的解决办法：添加国内镜像

$ docker pull php:7.1-fpm-alpine
Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)

见到这段烦人的超时提示，就知道是网络问题了，解决办法是添加国内镜像

https://docker.mirrors.ustc.edu.cn
https://hub-mirror.c.163.com
http://f1361db2.m.daocloud.io

镜像能够添加多个

设置步骤:
Docker for Windows/Mac

Setting/Preference -> Daemon -> Registry mirrors