Add compression-format and force-compression parameters to buildah tasks

[jiridanek]

https://issues.redhat.com/browse/KFLUXSPRT-6743
https://issues.redhat.com/browse/STONEBLD-4276

• Add zstd:chunked compression to built images. #1264

Description

Add COMPRESSION_FORMAT and FORCE_COMPRESSION parameters to the buildah tasks (buildah-oci-ta, buildah-remote-oci-ta) to enable zstd:chunked compression for container images.

Motivation

Large container images (especially CUDA/GPU images that can be 10-15GB+) take a long time to pull. Using zstd:chunked compression provides significant benefits:

1. Faster pulls: zstd:chunked enables lazy pulling and partial layer downloads
2. Reduced startup time: Container runtimes can start containers before fully downloading all layers
3. Better deduplication: Chunked format enables file-level deduplication across layers

For CUDA-based images, the --force-compression flag is crucial because base layers from upstream (e.g., nvidia/cuda) are typically gzip-compressed and need to be re-compressed to zstd:chunked format.

And when my Red Hat-provided base image is not on zstd:chunked yet, I want to still recompress it for myself.

Proposed Solution

Add two new parameters to buildah tasks:

- name: COMPRESSION_FORMAT
  description: The compression format for image layers (e.g., gzip, zstd, zstd:chunked)
  type: string
  default: ""

- name: FORCE_COMPRESSION  
  description: Force re-compression of all layers, including base image layers. Required when converting gzip layers to zstd:chunked.
  type: string
  default: "false"

These would be passed to the buildah push command:

buildah push \
  ${COMPRESSION_FORMAT:+--compression-format "$COMPRESSION_FORMAT"} \
  ${FORCE_COMPRESSION:+--force-compression} \
  ...

Use Case

We build GPU-accelerated notebook images for OpenDataHub/RHODS. Our CUDA images inherit from nvidia/cuda base images (gzip compressed) and grow to 10-15GB. Enabling zstd:chunked compression would significantly improve user experience when launching workbenches.

For testing the CUDA-enabled images, it will help reduce the 10+ minute wait for pull.

References

• buildah-push man page - documents --compression-format and --force-compression
• Fedora zstd:chunked change
• containers/buildah#4613 - related issue about layer reuse behavior