Flatcar support for EKS on versions above 1.21

[EhsanLunar]

Description

When an EC2 instance boots up with a flatcar image (even the latest) the kubelet fails.
The userdata defines (and should do so) that the /etc/eks/bootstrap.sh should run, which it does.

This seems to add a ExecStartPre to the kubelet.service:
ExecStartPre=/usr/share/oem/eks/download-kubelet.sh

Both the bootstrap.sh and the download-kubelet.sh are consistent with:
https://github.com/flatcar-linux/coreos-overlay/blob/main/coreos-base/flatcar-eks/files/bootstrap.sh
https://github.com/flatcar-linux/coreos-overlay/blob/main/coreos-base/flatcar-eks/files/download-kubelet.sh

The download-kubelet.sh fails with Unsupported Kubernetes version because in the case statement on line 24->50 (https://github.com/flatcar-linux/coreos-overlay/blob/main/coreos-base/flatcar-eks/files/download-kubelet.sh#L25) only has values for kubernetes version 1.15 -> 1.21

If I manually alter the file and add 1.22 (when I test this on 1.22.9 kubernetes version deployment) and re-run the bootsrap.sh it works fine as far as I can see, the node than joins the cluster and shows up as Ready and pods starting running on the node.

The last PR I can see on this particular thing was done about a year ago f0da7f8

Impact

No EKS support for kubernetes versions higher than 1.21

Environment and steps to reproduce

1. Set-up: Create an EKS cluster with the latest flatcar AMI in the worker nodes
2. Task: SSH into the node (probably through a Bastion)
3. Action(s): No actions needed
4. Error: kubelet.service fails because the download-kubelet.sh doesn't have download locations for kubernetes version above 1.21

Expected behavior

Download locations for kubernetes versions 1.22 and 1.23 (EKS doesn't have support for 1.24 yet it seems) should be located inside the download-kubelet.sh

Additional information

By running aws s3 ls s3://amazon-eks/ you can list the available locations of the other versions, so for it should result in this:

case $CLUSTER_VERSION in
  1.23)
    S3_PATH="1.23.9/2022-07-27"
    ;;
  1.22)
    S3_PATH="1.22.12/2022-07-27"
    ;;
  1.21)
    S3_PATH="1.21.2/2021-07-05"
    ;;
  1.20)
    S3_PATH="1.20.4/2021-04-12"
    ;;
  1.19)
    S3_PATH="1.19.6/2021-01-05"
    ;;
  1.18)
    S3_PATH="1.18.9/2020-11-02"
    ;;
  1.17)
    S3_PATH="1.17.12/2020-11-02"
    ;;
  1.16)
    S3_PATH="1.16.15/2020-11-02"
    ;;
  1.15)
    S3_PATH="1.15.12/2020-11-02"
    ;;
  *)
    echo "Unsupported Kubernetes version"
    exit 1
    ;;
esac

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Closes: flatcar/Flatcar#829

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)

[tormath1]

Thanks a lot for your contribution! It looks good to me. There's only one missing thing: a changelog entry (as it will be included in the next set of releases).
You might find changelog entry examples in the following directory: https://github.com/flatcar-linux/coreos-overlay/tree/main/changelog/bugfixes

[EhsanLunar]

@tormath1 Something like this? :)

[EhsanLunar]

@tormath1 Thanks! :)

[EhsanLunar]

@tormath1
If this is merged now, when will it be available?
Im guessing it will be available in the next alpha, beta and stable?

Reason I'm asking is because, running flatcar on EKS using Cluster API doesn't work at all atm because:

1. Flatcar doesn't support versions above 1.21
2. Bootstrapping aws cluster (which is necessary in ClusterAPI) isn't supported in EKS versions below 1.22

[tormath1]

@EhsanLunar that is correct. Once merged, this will be backported to current channels and available in the next releases.

[tormath1]

Thanks @EhsanLunar for this contribution, this is great! 🚀

Cherry-picked to:

• flatcar-3305
• flatcar-3277
• flatcar-3227