How to prevent Dockerfile caching git clone

Question

I have a Dockerfile trying to package and deploy a web app to a container. The code of app fetches from git repository during Docker image building. Here's the Dockerfile snapshot:

........ RUN git clone --depth=1 git-repository-url $GIT_HOME/ RUN mvn package -Dmaven.test.skip ........ 

I want the docker do not cache the step of RUN git clone --depth=1 git-repository-url $GIT_HOME/ so that the on-going updated on the the repository can be reflected on the Docker image building. Is it possible to a achieve that?

Answer 1

Another workaround:

If you use GitHub (or gitlab or bitbucket too most likely) you can ADD the GitHub API's representation of your repo to a dummy location.

ADD https://api.github.com/repos/$USER/$REPO/git/refs/heads/$BRANCH version.json RUN git clone -b $BRANCH https://github.com/$USER/$REPO.git $GIT_HOME/ 

The API call will return different results when the head changes, invalidating the docker cache.

If you're dealing with private repos you can use github's x-oauth-basic authentication scheme with a personal access token like so:

ADD https://$ACCESS_TOKEN:[email protected]/repos/$USER/$REPO/git/refs/heads/$BRANCH version.json 

(thx @captnolimar for a suggested edit to clarify authentication)

Answer 2

Issue 1996 is not yet available, but you have the following workaround:

FROM foo ARG CACHE_DATE=2016-01-01 RUN git clone ...  docker build --build-arg CACHE_DATE=$(date) .... 

That would invalidate cache after the ARG CACHE_DATE line for every build.

Or:

ADD http://www.convert-unix-time.com/api?timestamp=now /tmp/bustcache RUN git pull 

That would also invalidate cache after this ADD line.

Similar idea:

Add ARG command to your Dockerfile:

# Dockerfile # add this and below command will run without cache ARG CACHEBUST=1 

When you need to rebuild with selected cache, run it with --build-arg option

$ docker build -t your-image --build-arg CACHEBUST=$(date +%s) . 

then only layer below ARG command in Dockerfile will rebuild.