Add cache-from option

[nzwsch]

Allowing the option --cache_from to the builder in this PR will reduce the time to build the Docker image.

https://lipanski.com/posts/speed-up-your-docker-builds-with-cache-from

[dhh]

If you're using your own host as a builder, you'll get layer caching automatically. No need to specify this cache-from. Seems like an optimization meant to be used in conjunction with some CI hosts? Have you run into a situation where using your own builder, either local or remote, didn't work with layer caching?

[nzwsch]

I ran the command locally and was able to use the cached image from the build as you suggested.
In my use case, I wanted to push the command to GitLab to build, run tests based on the image tag, and if the tests are successful, deploy with the mrsk command using the tag. However, I can work around this by doing an empty build of the image once pulled on CI. I think it would be hard to support bypassing all docker options with the mrsk command, so this PR can be closed.

[bdeak4]

Hi @nzwsch, did you manage to get cache working in CI builds?

I've tried something along the lines:

docker pull $DOCKER_IMAGE:latest
docker build -t $DOCKER_IMAGE:latest --cache-from $DOCKER_IMAGE:latest .
mrsk deploy

But mrsk does not seem to pick up cache from docker build

[nzwsch]

@bdeak4
DHH mentioned above that the build image should be used as a cache if an image layer exists. It is not necessary to run the build in the local environment.

docker pull $DOCKER_IMAGE:latest
mrsk deploy

Please make sure that the image tag is one that you have pulled into your mrsk config file.