Ensure that parsed container ID is 64 chars.

[breedx-splk]

Resolves #7437.

A few caveats about this. The TL;DR on #7437 is that a non-containerized process was reporting a container.id attribute. The submitter narrowed it down and I was able to confirm with the test case in this PR.

I hunted for other means for code to determine if it's containerized with the idea to not even do the parsing if not containerized, but I couldn't find anything useful. In fact, most approaches of detecting containerization at all do involve parsing cgroups. Wacky.

So I attempted to verify that container IDs should always be 64 characters. I found:

• podman - docs here "Container ID (full 64-char hash)"
• docker - UID generator source here shows 32 bytes (and even guards against fully numeric!)
• lxc man page says "container identifier format is an alphanumeric string". If this maps into cgroups (no idea!), it would have already been broken in some cases because we enforce hex.

I'm a little concerned about this approach because the otel spec suggests that "The UUID might be abbreviated.", but it's unclear/non-specific about the circumstances that might cause this.

Open to hearing about why the approach presented here is a bad idea. 🙃

[trask]

makes sense to me, thanks for posting your research 👍

I'm a little concerned about this approach because the otel spec suggests that "The UUID might be abbreviated."

I wonder if this was to accommodate external observers which may not be getting it from cgroups?

or maybe it's saying the instrumentation library "may" abbreviate it for compactness?

@arminru it looks like this text came from you, do you happen to remember more context? open-telemetry/opentelemetry-specification#673 (comment)

[arminru]

@trask Three years later I don't remember any details, but I think I was referring to the UUID short identifier here:
https://docs.docker.com/engine/reference/run/#container-identification
I don't think this short identifier is used by any programmatic means in practice, but rather just when a user is interacting with the console, so you might be fine with relying on the full identifier. I assume your means of retrieving the ID will always yield the full UUID anyway.