buildah push with compression

[andrew-womeldorf]

I'm only somewhat familiar with buildah, so it's very possible I'm just doing something wrong. Want to check here before opening an issue.

My desired outcome is to create a gzipped tar. However, the various sets of arguments I use don't seem to have any impact on the resulting filesize.

$ podman -v
podman version 3.4.4
$ podman run --rm -it quay.io/containers/buildah:v1.33.2
[root@aca67de937a2 /]# buildah pull ubuntu
Resolved "ubuntu" as an alias (/etc/containers/registries.conf.d/000-shortnames.conf)
Trying to pull docker.io/library/ubuntu:latest...
Getting image source signatures
Copying blob a48641193673 done   |
Copying config 174c8c134b done   |
Writing manifest to image destination
174c8c134b2a94b5bb0b37d9a2b6ba0663d82d23ebf62bd51f74a2fd457333da
[root@aca67de937a2 /]# buildah images
REPOSITORY                 TAG      IMAGE ID       CREATED       SIZE
docker.io/library/ubuntu   latest   174c8c134b2a   4 weeks ago   80.4 MB

Using various flags with buildah push to try to change the filesize, but they're all the same filesize in the end:

[root@aca67de937a2 /]# buildah push ubuntu docker-archive:image.tar
...
[root@aca67de937a2 /]# buildah push ubuntu docker-archive:image.tar.gz
...
[root@aca67de937a2 /]# buildah push --compression-format gzip ubuntu docker-archive:compression-format-gzip.tar.gz
...
[root@aca67de937a2 /]# buildah push --compression-format gzip --force-compression ubuntu docker-archive:force-compression.tar.gz
...
[root@aca67de937a2 /]# buildah push --disable-compression ubuntu docker-archive:disable-compression.tar
...
[root@aca67de937a2 /]# ls -lh | grep tar
-rw-r--r--   1 root   root    77M Jan  9 18:22 compression-format-gzip.tar.gz
-rw-r--r--   1 root   root    77M Jan  9 18:23 disable-compression.tar
-rw-r--r--   1 root   root    77M Jan  9 18:22 force-compression.tar.gz
-rw-r--r--   1 root   root    77M Jan  9 18:19 image.tar
-rw-r--r--   1 root   root    77M Jan  9 18:21 image.tar.gz

I would expect at least one of these combinations of flags would result in a file with a differing size.

[rhatdan]

@mtrmac @vrothberg PTAL

[mtrmac]

None of those options affect the output format of docker-archive. (They would, in principle, affect the compression format inside the archive, except that docker-archive format never contains compressed layers.)

Pipe it into a separate gzip stage if you want, by writing to docker-archive:/dev/stdout | gzip perhaps.

[andrew-womeldorf]

Awesome, that's what I was missing. Thank you!