Unclear behaviour for `save`/`load` when using SHA (tag or not)
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Description
Description
I will often save my Docker images in a gzipped tar file, in order to load them in a different environment.
Then recently I added checksums along with my tags, in order to pin my versions, while having a version manager update to the latest SHA for the given tag.
This combination is causing issues though.
Actually, using the SHA alone causes this not to work in the same way as using the combination.
AFAICT only the tag alone works.
Reproduce
I have a simple script to reproduce this:
#!/usr/bin/env bash
set -Eeuo pipefail
IMAGE="${1:-docker.io/library/alpine:3.21.3@sha256:2436f2b3b7d2537f4c5b622d7a820f00aaea1b6bd14c898142472947d5f02abe}"
# Pull image
docker pull "$IMAGE"
# Ensure that test runs with pulled image
docker run --pull=never --rm "$IMAGE" echo "If you see this it works!"
# Save pulled image
TAR="$(docker save "$IMAGE" | gzip | base64)"
# Remove local image
docker inspect "$IMAGE" --format='{{.Id}}' | xargs -r docker rmi
# Load saved image to local
echo "$TAR" | base64 --decode | docker load
# See that test fails with saved/loaded image
docker run --pull=never --rm "$IMAGE" echo "If you see this it also works!"
Expected behavior
I expected docker pull to include a reference using the provided tag, even though it is actually pulling via the SHA.
docker version
Client: Docker Engine - Community
Version: 28.0.1
API version: 1.48
Go version: go1.23.6
Git commit: 068a01e
Built: Wed Feb 26 10:41:16 2025
OS/Arch: linux/amd64
Context: default
Server: Docker Engine - Community
Engine:
Version: 28.0.1
API version: 1.48 (minimum version 1.24)
Go version: go1.23.6
Git commit: bbd0a17
Built: Wed Feb 26 10:41:16 2025
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.7.25
GitCommit: bcc810d6b9066471b0b6fa75f557a15a1cbf31bb
runc:
Version: 1.2.4
GitCommit: v1.2.4-0-g6c52b3f
docker-init:
Version: 0.19.0
GitCommit: de40ad0
docker info
Client: Docker Engine - Community
Version: 28.0.1
Context: default
Debug Mode: false
Plugins:
buildx: Docker Buildx (Docker Inc.)
Version: v0.21.1
Path: /usr/libexec/docker/cli-plugins/docker-buildx
compose: Docker Compose (Docker Inc.)
Version: v2.33.1
Path: /usr/libexec/docker/cli-plugins/docker-compose
Server:
Containers: 1
Running: 1
Paused: 0
Stopped: 0
Images: 174
Server Version: 28.0.1
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Using metacopy: false
Native Overlay Diff: true
userxattr: false
Logging Driver: json-file
Cgroup Driver: systemd
Cgroup Version: 2
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
Swarm: inactive
Runtimes: io.containerd.runc.v2 runc
Default Runtime: runc
Init Binary: docker-init
containerd version: bcc810d6b9066471b0b6fa75f557a15a1cbf31bb
runc version: v1.2.4-0-g6c52b3f
init version: de40ad0
Security Options:
apparmor
seccomp
Profile: builtin
cgroupns
Kernel Version: 6.1.0-28-amd64
Operating System: Debian GNU/Linux 12 (bookworm)
OSType: linux
Architecture: x86_64
CPUs: 16
Total Memory: 31.13GiB
Name: <company PC>
ID: <>
Docker Root Dir: /var/lib/docker
Debug Mode: false
Experimental: false
Insecure Registries:
::1/128
127.0.0.0/8
Registry Mirrors:
<company mirror>
Live Restore Enabled: false
Additional Info
I tried both with and without the company mirror for Docker Hub to no avail.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the behavior with the provided Bash script, focusing on docker pull, docker save, docker load, and subsequent docker run commands using tag and SHA references. No source files or tests are named, so trace the Docker CLI handling of image references and save/load metadata. Done means a pulled image addressed by tag plus SHA remains runnable after save and load.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- bash, docker
- Domain
- cli
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100