Docker鏡像拉取失敗或超時的解決辦法：添加國內鏡像

$ 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)

見到這段煩人的超時提示，就知道是網絡問題了，解決辦法是添加國內鏡像

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

鏡像能夠添加多個

設置步驟:
Docker for Windows/Mac

Setting/Preference -> Daemon -> Registry mirrors