Support image tar, without accessing Docker daemon

[vulyon]

Enable Docker Daemon-Free Image Squashing

This PR directly addresses and resolves Issue #24: "Make it possible to run squashing without accessing Docker daemon" by introducing the ability for docker-squash to directly process Docker images from tar files. This eliminates the need for a running Docker daemon, significantly enhancing flexibility for image optimization in CI/CD pipelines, air-gapped environments, and systems without Docker installed.

Key Benefits

• No Docker Daemon Required: Squash images anywhere you can save them as a tar file.
• Ideal for Restricted Environments: Works seamlessly in CI/CD, air-gapped setups, or when Docker isn't running.
• OCI Format Support: The tool automatically detects and processes images from OCI-formatted input tar files. Please note: Currently, testing has been focused solely on OCI format images.
• Preserves Layer History: Ensures compatibility and traceability for your squashed images.

How to Use

1. Export the Image:

   $ docker save -o source.tar jboss/wildfly:latest
   

2. Squash from Tar:

   $ python -m docker_squash.cli --input-tar source.tar --tag jboss/wildfly:squashed -f 8 --output-path squashed.tar --load-image false
   

   • Use --input-tar for your source image file.
   • --tag is recommended for the new image name.
   • --output-path specifies where to save the squashed tar file.
   • --load-image false prevents the tool from attempting to load the image directly into a Docker daemon.

3. Load into Docker (Optional):

   $ docker load -i squashed.tar
   

This enhancement significantly broadens docker-squash's utility, making image size optimization more accessible across diverse development and deployment scenarios.

[vulyon]

hello,sir @goldmann @rnc it appears there's an issue with the runner environment. It looks like the CI/CD checks are failing due to the Ubuntu 20.xx runner deprecation (as per the error message). This doesn't seem to be related to my code changes.

[rnc]

@lyon-v I've fixed the runners and rebased. However I think you need to run ./support/run_formatter.py to fixup the formatting as well.

[vulyon]

@rnc Hi there! Apologies for the delayed response. I've fixed the code formatting and it has passed the checks now.

[vulyon]

Sir @rnc @goldmann .Do I need to squash these two commits into a single one?

[rnc]

@lyon-v Did you wish to discuss any of the comments?

[vulyon]

sir, my apologies for the slow response. I've been swamped with work lately, but I'll reply to or fix these issues shortly.