Flatcar compatibility

[Piotr Kowalczyk]

Good morning, 

So there is a very interesting compatibility chart: https://www.flatcar.org/docs/latest/container-runtimes/getting-started-with-kubernetes/ - which we've just found, not being aware of it earlier. 

The problem is, that we currently have LTS (Flatcar 3033.3.13 (LTS 2022) with K8s v1.26.5 set up by kubespray (with calico) and don't really have any issues with it. Which gives us, according to this table above, a non-working system which actually works. 

Is it safe to deploy this to production or not then? Are there any specific issues I should be aware of? Is this docs up to date? Any ideas on how to approach this?

Best to all, 

Piotr Kowalczyk

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[Flatcar Container Linux User]

Hi Piotr,

Yes the docs are up to date. Our chart is about compatibility of Flatcar (as shipped) with vanilla Kubernetes, as that is what we can test during a release. During testing of K8s v1.26 we found that it requires containerd 1.6+ while LTS ships with containerd 1.5 and per LTS update policy it won't be updated (https://github.com/flatcar/Flatcar/issues/916).

I don't know what exactly kubespray does but if it deploys its own containerd, then that would allow it to work. If it works for you then we do our best to make sure an LTS update won't break it.

Hope that helps,

Jeremi

[Mathieu Tortuyaux]

Hello Piotr and thanks for your question,

Flatcar LTS 3033 has been excluded from the CI when we were hitting this issue (see: https://github.com/flatcar/mantle/pull/408):

```

1Jan 17 00:32:53.106028 kubelet[1553]: E0117 00:32:53.105999    1553 run.go:74] "command failed" err="failed to run Kubelet: validate service connection: CRI v1 runtime API is not implemented for endpoint \"unix:///var/run/containerd/containerd.sock\": rpc error: code = Unimplemented desc = unknown service runtime.v1.RuntimeService"
```

Which was caused by a too old version of containerd shipped by the OS - is that possible that you use a different version of containerd?

Thanks and have a nice day,

Mathieu Tortuyaux

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[Piotr Kowalczyk]

Mathieu,

This is configuration I'm using:

  links:
    # Make sure that the future built-in Docker/containerd sysext images won’t be enabled.
    - path: /etc/extensions/docker-flatcar.raw
      target: /dev/null
    - path: /etc/extensions/containerd-flatcar.raw
      target: /dev/null

So apparently we're not using containerd shipped with Flatcar OS. There's containerd v1.7.1, which is shipped by kubespray 2.22 (with k8s 1.26).

And I now see Flatcar ships containerd 1.6.x across all releases, which gives a  lot of sense to the compatibility table, putting me on pretty good ground at the same time. 

Many thanks for this clarification!

Best, 

Piotr Kowalczyk

[Mathieu Tortuyaux]

Piotr,

Awesome! I'm going to update the documentation to mention that the compatibility matrix is done based on software shipped by Flatcar (and not from third-party configuration). Happy to hear that Kubespray is working fine with Flatcar, any chance to share some details on your installation if you've faced some issues (here or on Slack / Matrix channel) ? We could reference this installation method under this section: https://www.flatcar.org/docs/latest/container-runtimes/getting-started-with-kubernetes/#deploy-a-kubernetes-cluster-with-flatcar

Thanks and have a great day,

Mathieu