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Add minimal systemd version about configuring cgroup driver docs #44979

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Add minimal systemd version about configuring cgroup driver docs #44979

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4 changes: 4 additions & 0 deletions content/en/docs/setup/production-environment/container-runtimes.md
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Expand Up @@ -125,6 +125,10 @@ cgroup driver instead of `cgroupfs`.

### systemd cgroup driver {#systemd-cgroup-driver}

{{< note >}}
The minimum `systemd` version should be v228 and above, see [details](https://github.com/systemd/systemd/commit/17f62e9bd00f5fefd486475861b06d3ec6b7ee10)
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Hi @pegasas, can we make it a bit new-user friendly also, like adding a document what changes are being introduced in systemD.

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@pegasas pegasas Feb 6, 2024 •
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I can not really get your point.

  • If you are talking we should add some description about how systemd cgroup driver integrated into CRI, it would a large topic which deserves another issue for tracking.

  • If you are talking which specific change are introduced by systemd v228, I think it is unneccsary, assume if you are a user, what I concern is how I could use this function as soon as possible. If indeed the customer has such kinds of demands, he/she will looks deep into source code just like the discussions on issues.

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@utkarsh-singh1 utkarsh-singh1 Feb 13, 2024 •
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@pegasas, thanks for the clarity, was talking about any discussion before/after about this commit you have mentioned, if there are any?

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no, actually.
What are your suggestion?
maybe you're talking #1?

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I agree with @utkarsh-singh1 here. Not everyone can understand the code and a purpose of certain code change. How about pointing to the systemd release notes ?

Here is how the change is explained there:

Slice units may now be created transiently via the bus APIs,
similar to the way service and scope units may already be
created transiently.

This is also requires some background for understanding, but it's much better than pointing to the code in my opinion.

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@pegasas I would recommend linking to the systemd release notes or the releases page than pointing to the actual code. Also, a small nit

Suggested change
The minimum `systemd` version should be v228 and above, see [details](https://github.com/systemd/systemd/commit/17f62e9bd00f5fefd486475861b06d3ec6b7ee10)
The minimum `systemd` version should be v228 or above, see [details](https://github.com/systemd/systemd/releases/tag/v228)

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May be some explanations should be added to clarify why the change is important for Kubernetes, wdyt?

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Stating the required version should be sufficient IMO. What are some examples of the the explanations you'd like to see?

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I simply want to know why v228 is a minimum required version.
Here is an example: https://kubernetes.io/docs/concepts/architecture/cgroups/#using-cgroupv2
That documentation not just recommends certain software versions, but gives enough info for a reader to understand a reasoning behind it, e.g. CRI-O >= v1.20 and Containerd >= v1.4 support cgroup2.

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That's a good point. AFAIK the minimum required version is v228 per the linked issue because the kubelet fails to start with lower versions.

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@network-charles network-charles Oct 3, 2024 •
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Explained why this version is important. I also pointed to the version release note as it is easier to understand than reading code written in C.

Suggested change
The minimum `systemd` version should be v228 and above, see [details](https://github.com/systemd/systemd/commit/17f62e9bd00f5fefd486475861b06d3ec6b7ee10)
To use the systemd cgroup driver, `systemd` should be version 228 or later.
Before v228, systemd wasn’t good at handling transient units for slices. Normally, systemd would statically load this from a file, so this caused problems when Kubernetes tried to create slices dynamically.
See [systemd v228 release notes](https://github.com/systemd/systemd/blob/v228/NEWS).

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I'd write:

To use the systemd cgroup driver, `systemd` should be version 228 or later.

(mentioning “minimum” is tautological).

The rest of the change looks good. However, I'd move the entire note to come after we introduce systemd.

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Alright

{{< /note >}}

When [systemd](https://www.freedesktop.org/wiki/Software/systemd/) is chosen as the init
system for a Linux distribution, the init process generates and consumes a root control group
(`cgroup`) and acts as a cgroup manager.
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