podman build --output to an oci-archive isn't easy to figure out

[dustymabe]

Description

I was looking for an easy way to build and output to an oci-archive in a single step. So rather than podman build -t + podman push foo oci-archive:./foo.ociarchive, I need to just do that in one step.

I discovered the --output option, which in the man page describes:

the value of --output can be just a destination (in the **dest** format)"

So I try:

podman build -f Containerfile --output=oci-archive:./foo.ociarchive

and that fails with an obscure error (I'm in a locked down environment):

+ podman build /srv/tmp/tmpw2r2ieuu --output oci-archive:/srv/builds/37.20230414.dev.0/x86_64/fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.ociarchive     
STEP 1/2: FROM scratch                                                                                                                                       
STEP 2/2: ADD fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.qcow2 /disks/                                                                                                                                                                                                                                                
COMMIT                                                                                                                                                       
Error: failed to export build output: failed while performing untar at "/srv/oci-archive:/srv/builds/37.20230414.dev.0/x86_64/fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.ociarchive": processing tar file(lchown /disks: operation not permitted): exit status 1

What's important here is not the failure, but the fact that podman isn't doing what I'm asking for.

I also tried with --output type=oci,dest=./foo.ociarchive and that didn't work either.

Then @nalind told me that --tag supports destination format (undocumented) and that works:

+ podman build /srv/tmp/tmp5zrcblve --tag oci-archive:/srv/builds/37.20230414.dev.0/x86_64/fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.ociarchive
STEP 1/2: FROM scratch
STEP 2/2: ADD fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.qcow2 /disks/
COMMIT oci-archive:/srv/builds/37.20230414.dev.0/x86_64/fedora-coreos-37.20230414.dev.0-kubevirt.x86_64.ociarchive
--> 

+ exit 0

I think there's a few places where there is room for improvement here:

1. Document that --tag supports destination format and not just tags. Is there a good reason not to?
2. Add support for --output to output to destination format locations. Is there a good reason not to?
3. Document the limitations of --output.

Output of rpm -q buildah or apt list buildah:

podman-4.4.4-3.fc37.x86_64

[nalind]

The dest format mentioned in the docs about --output is in the format of a dest value that would also be passed to --output. The doc for --output only mention local and tar as recognized types, as the set of type values isn't going to be the same as the set of transports enumerated in containers-transports(5).

[dustymabe]

Hmm. I guess I was confusing **dest** format in the docs with the formats specified in containers-transports(5). I didn't know there was another set of formats. Is there a place we could link to with more information on those formats?

It seems these different options/formats are competing. Should we spell it out in the docs?

[github-actions]

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[rhatdan]

@nalind @flouthoc thoughts?

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[rhatdan]

@vrothberg @flouthoc @umohnani8 @nalind PTAL

[vrothberg]

I support @dustymabe's proposal to make the docs clearer on this issue.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[github-actions]

A friendly reminder that this issue had no activity for 30 days.