Docker build encounters "operation timed out"

Issue

while running docker build, we see following error.

fetch http://dl-4.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz WARNING: Ignoring http://dl-4.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz: operation timed out fetch http://dl-4.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz WARNING: Ignoring http://dl-4.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz: operation timed out ERROR: unsatisfiable constraints:

Solution 

Pass proxy as environment variable and unset at the end of Dockerfile file.

ENV http_proxy http://proxyhost.com:3128 ENV https_proxy http://proxyhost.com:3128 ... RUN unset http_proxy https_proxy

Root cause Analysis

1. During docker build on a machine which is behind proxy server can encounter this issue. Requests do not go through  running Docker engine but go directly. hence, you need to mention proxy in Dockerfile and unset later.
2. Second issue may happen that upstream server is not available. This is very rare. You can view with below command to see current repositories

RUN cat /etc/apk/repositories

Default values are

http://dl-cdn.alpinelinux.org/alpine/v3.4/main http://dl-cdn.alpinelinux.org/alpine/v3.4/community

You can check through browser if you can see if domain is resolving or not. you can replace with actual domain like below

RUN sed -i 's/dl-cdn.alpinelinux.org/dl-4.alpinelinux.org/' /etc/apk/repositories