I have a docker Dockerfile in which I want to clone a Git repo. If the Git repo is not updated I would like Docker to use its cache. If the repo is updated then building the Docker Image should use the Git repo updates.
Based on this stackoverflow question:
I have added the following to my Dockerfile:
#invalidate cache if micropython is updated ADD https://api.github.com/repos/dwjbosman/micropython/git/refs/heads/master /root/micropython_version.json RUN git clone --recurse-submodules https://github.com/dwjbosman/micropython.git /root/micropython && cd /root/micropython && git submodule update
I use a makefile with targets to build the image. First I pull the previous image from docker hub:
docker pull $(REGISTRY)/$(DOCKER_IMAGE)
and then I use this pulled image as a cache for the new build:
docker build --cache-from $(DOCKER_IMAGE) -t $(DOCKER_IMAGE)
I am building the images in a CI environment (Gitlab). If I check the logs the ADD step always invalidates the cache and the checksum changes even if no updates were done in the Git repo.
I have checked the output of “https://api.github.com/repos/dwjbosman/micropython/git/refs/heads/master“. The contents does not seem to change.
Is there some hidden property (time perhaps?) which still changes?