TIL you can make a Dockerfile's FILE dynamic
Oliver Peate posted on May 23rd, 2019
-FROM ruby:2.6-alpine +ARG FROM_IMAGE=ruby:2.6-alpine +FROM $FROM_IMAGE
This Dockerfile still defaults to
ruby:2.6-alpine after introducing an
ARG, but now we can change the
FROM image easily:
docker build -t my_project:2.5-latest --build-arg FROM_IMAGE=ruby:2.5-alpine .
Handy for testing libraries against multiple language versions.