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Exercise in container image saving, loading from file, and embedding as compressed base64 encoded text string
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container-image-file-save-load-transport.md

Container image file and transportation

Conclusion:

Images can be saved to file or base64 encoded for building directly into golang binaries, python/bash scripts, and carrying independently across disconnected systems.

Unfortunately, the only way to preserve image metadata is to save as a docker-archive transport type, and to podman load the resulting archive via following step:

cat pause-3.2.tar | podman load
cat registry-latest.tar | podman load

Save images as transport type tar file docker-archive and load from docker-archive tar file

podman image prune --all --force && podman images

skopeo copy --additional-tag docker.io/library/registry:latest docker://docker.io/library/registry:latest docker-archive://$(pwd)/registry-latest.tar
skopeo copy --additional-tag k8s.gcr.io/pause:3.2 docker://k8s.gcr.io/pause:3.2 docker-archive://$(pwd)/pause-3.2.tar
skopeo copy --additional-tag docker.io/library/registry:latest docker-archive://$(pwd)/registry-latest.tar containers-storage:docker.io/library/registry:latest
skopeo copy --additional-tag k8s.gcr.io/pause:3.2 docker-archive://$(pwd)/pause-3.2.tar containers-storage:k8s.gcr.io/pause:3.2

Save images as transport type tar file oci-archive and load from oci-archive tar file

podman image prune --all --force && podman images

skopeo copy --additional-tag docker.io/library/registry:latest docker://docker.io/library/registry:latest oci-archive://$(pwd)/registry-latest.tar
skopeo copy --additional-tag k8s.gcr.io/pause:3.2 docker://k8s.gcr.io/pause:3.2 oci-archive://$(pwd)/pause-3.2.tar
skopeo copy --additional-tag docker.io/library/registry:latest oci-archive://$(pwd)/registry-latest.tar containers-storage:docker.io/library/registry:latest
skopeo copy --additional-tag k8s.gcr.io/pause:3.2 oci-archive://$(pwd)/pause-3.2.tar containers-storage:k8s.gcr.io/pause:3.2

EXPERIMENTAL / MAD HAT SCIENCE

DISCLAIMER: this method requires bizzare handling of images and storage and cannot be expected to work at any given time in the future

Pull images

podman pull k8s.gcr.io/pause:3.2
podman pull docker.io/library/registry:latest

Save images as compressed base 64 encoded text strings

podman save k8s.gcr.io/pause:3.2 | xz -z9ec -T4 | base64 -w 0 > pause.tar.xz.txt
podman save docker.io/library/registry:latest | xz -z9ec -T4 | base64 -w 0 > registry.tar.xz.txt

Check files

kmorgan@mprcs:/tmp/test$ du -sh *
308K    pause.tar.xz.txt
9.2M    registry.tar.xz.txt

Remove all locally cached images

podman image prune --all --force
podman images

Load images from txt string

kmorgan@mprcs:/tmp/test$ base64 -d pause.tar.xz.txt | xz -dc | podman load --quiet
Loaded image(s): k8s.gcr.io/pause:latest
kmorgan@mprcs:/tmp/test$ base64 -d registry.tar.xz.txt | xz -dc | podman load --quiet
Loaded image(s): quay.io/cloudctl/registry:latest

Verify images are present

kmorgan@mprcs:/tmp/test$ podman images
REPOSITORY                  TAG     IMAGE ID      CREATED        SIZE
docker.io/library/registry  latest  5c4008a25e05  2 weeks ago    26.8 MB
k8s.gcr.io/pause            3.2     80d28bedfe5d  13 months ago  686 kB
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