Is it possible to use BuildKit to build images and export them as a single tarball without relying on external image registries?

[otischan]

Is it possible to use BuildKit to build images and export them as a single tarball without relying on external image registries?
I have a process in mind and would love to know if there’s a way to achieve this using BuildKit. Here's the process I’m aiming for:

1. Run buildkitd to start the BuildKit daemon.
2. Use buildctl to import a base image, for example, baseimage:v1.
3. Build an app image based on the imported base image, with a Dockerfile like:

FROM baseimage:v1
RUN mkdir test
CMD echo test

4. Export all the images (both the base image and the app image) into a single tarball.
5. Use the go-containerregistry package to push all the images in the tarball to any registry.

Any suggestions or guidance on how to achieve this would be greatly appreciated! Thanks in advance!

[otischan]

I have tried several different settings for the buildctl build command, such as output=oci/local, export-cache=local/ref, etc., but none of them successfully achieved my goal.

[profnandaa]

Tried this? https://github.com/moby/buildkit?tab=readme-ov-file#oci-tarball

[otischan]

I have already tried it, but the result is not what I expected. Is there something wrong with my workflow?
What I hope is that, I have 100 images, which may all be built from the same base image. When exporting the tar files using BuildKit, I want to compress all 100 images together, reusing the common layers, rather than having 100 separate tar files, each containing the same base image layers.

[profnandaa]

I see... afik that can only be achieved by a registry coz of its content addressing mechanism...