[receiver/dockerstats] Add pids_stats metrics

[sigilioso]

Component(s)

receiver/dockerstats

Is your feature request related to a problem? Please describe.

I would like to improve the dockerstats receiver with the addition of pids_stats metrics.

Describe the solution you'd like

Docker container's stats endpoint returns pids_stats if the Linux's Kernel is >= 4.3 and pids group is supported.

It can include up to two metrics:

• pids_current: current number of processes.
• pids_max: maximum number of processes.

I would like the receiver to support reporting those metrics when available.

Describe alternatives you've considered

No response

Additional context

This is part of a New Relic initiative to adopt the dockerstats receiver as a source of instrumentation.

I would be happy to work on it once the proposal gets refined/approved.

[github-actions]

Pinging code owners:

• receiver/dockerstats: @rmfitzpatrick @jamesmoessis

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[jamesmoessis]

Thanks for the proposal @sigilioso, would be happy to add this feature, and happy to review any PRs for it.

A couple of things to consider:

• We will need to bump the supported docker API version, since the pids_stats are only available in >=v1.23 (this receiver is currently on 1.22). This will technically be a breaking change, but since the 1.22 API spec is 8 years old now and this receiver is still in alpha, that's fine by me.
• There should be tests covering both cases of when these stats exist and when they don't, since they only exist in kernel version 4.3 and above.

That's all I can think of for now. Let me know if you have any more questions!

[sigilioso]

@jamesmoessis Thank you for the feedback and the considerations.
I'll definitely take both considerations into account when developing it and start working on it as soon as possible.

[crobert-1]

@sigilioso It looks like your PR #21111 was meant to address this, please close this issue if it's been resolved.

[sigilioso]

Thanks for the heads up @crobert-1 🙂