Describe your idea/feature/enhancement

I wish SAM CLI would enable me to enable Docker Buildkit when running sam build for a function with PackageType: Image.

This would enable me to use BuildKit features such as cache mounts for faster and more efficient builds.

Proposal

A very specific approach would be to add a new option along the lines of --use-docker-buildkit or something like that.

That said, something more general might be a good idea.

For example, I tried to enable buildkit by running export DOCKER_BUILDKIT=1 && sam build but it didn’t work.

IIRC docker build supports various other environment variables, so it might be a good idea to have a general purpose mechanism to set environment variables that’d be exposed to the docker build process.

One way to do this might be to simply forward/inherit the environment vars from the user’s shell to/into the docker build process.

Another way could be to add a CLI option like --docker-build-env DOCKER_BUILDKIT=1,FOO=bar

Additional Details

This will not require any updates to the SAM Spec.