Download files from URLs

docker

Context

When creating a Dockerfile, it is common to download artifacts, tar files, etc. from external URLs. Usually, developers will use a RUN instruction that invokes curl or wget to accomplish this. The dockerfile specification provides a baked-in alternative, the ADD instruction.

How to use

Besides copying files and directories from the build context, the ADD statement can download files from an external URL, as shown in the example below:

FROM ubuntu:latest

ADD https://github.com/roboll/helmfile/releases/download/v0.138.7/helmfile_linux_amd64 /usr/local/bin/helmfile

RUN chmod +x /usr/local/bin/helmfile

ENTRYPOINT ["/usr/local/bin/helmfile"]

Notes

  • The downloaded file will have 0600 as permission, which in case of a binary means that you will have to run a subsequent RUN command to update the executable bit (as shown in the example above).
  • If the URL is protected with authentication, you need to use wget or curl instead, since the ADD instruction doesn’t support authentication

Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer’s view in any way.