Changes/zstd:chunked

Default podman created images to zstd:chunked

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

Modify podman push to default to creating images with zstd:chunked, allowing users to modify containers.conf to continue to use the legacy gzip image format.

Owner

• Name: Daniel J Walsh
• Email: dwalsh@redhat.com
• Name: Giuseppe Scrivano
• Email: gscrivan@redhat.com

Current status

• Targeted release: Fedora Linux 41
• Last updated: 2024-06-26
• [<will be assigned by the Wrangler> devel thread]
• FESCo issue: <will be assigned by the Wrangler>
• Tracker bug: <will be assigned by the Wrangler>
• Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

The goal is to speed up the pulling of container images, via using zstd:chunked. zstd:chunked format has shown itself to speed up the pulling of images by as much as 90%. This change has been waiting for change for over 3 years, waiting for Docker to support the format.

Benefit to Fedora

Fedora would be the first distribution to support building zstd:chunked format by default. Container engines (Podman, Buildah, Skopeo, CRI-O) which support the format natively would see a great speed up in pulling images. Other container engines including Docker and Containerd would see some speed up do the the compression algorythms of zstd, but not to the same degree as container engines with full support.

Scope

• Proposal owners: Dan Walsh, Giuseppe Scrivano

• Other developers:

• Release engineering: #Releng issue number

• Policies and guidelines: N/A (not needed for this Change)

• Trademark approval: N/A (not needed for this Change)

• Alignment with Community Initiatives:

How To Test

Build and push container images to container registries. Inspect them to check that their format is zstd:chunked. Pull the image back to the host. Now make a small change to the image and push it back to the registry Remove the changed image leaving the original image in place. Now pull the updated image again. You should see a big change in download speed.

Now attempt to pull the same image with Docker/Moby to make sure the image works with those container engines.

User Experience

Users should experience a nice improvement in download speeds of container images that were previously created with zstd:chunked.

Contingency Plan

If we find issues with zstd:chunked while turned on in Rawhide, we can easily reverse direction and go back to the original default gzip format.

Documentation

N/A (not a System Wide Change)