[Bug] eksctl does not support maxPodsPerNode on AL2023

[davejbax]

What were you trying to accomplish?

Upgrading a cluster to 1.30 with managed node groups that set maxPodsPerNode. Presumably the same issue would occur creating a new cluster on 1.30 with the same config.

What happened?

eksctl produces the following error:

Error: eksctl does not support configuring maxPodsPerNode EKS-managed nodes based on AmazonLinux2023

which comes from the validation here.

How to reproduce it?

Create a ClusterConfig for Kubernetes 1.30 or higher with a managed node group that sets maxPodsPerNode to some value above zero.

Versions

$ eksctl info
eksctl version: 0.194.0
kubectl version: v1.31.1
OS: linux

Further comments

Having dug through the code a little bit, it seems that the reason this was added was because AL2023 EKS-managed nodes have their user data automatically populated to include a NodeConfig that sets maxPods: de74c5b#r1546826066

I'm slightly confused by this reasoning, however:

• nodeadm supports merging multiple NodeConfigs from a set of userdata (ref).
• From what I can tell, EKS inserts its NodeConfig into the user data of an instance above the user data specified by the template.
• Looking at the codepath for merging NodeConfigs, NodeConfigs get merged top-to-bottom from the MIME multi-part user data.

Therefore, I think that this means any NodeConfig specified in the launch template's user data should get merged with and override equivalent fields of the (auto-generated) NodeConfig that gets inserted into the instance user data by EKS, and hence that we can override maxPods.

If the reasoning above is sound, I think this would be a reasonably straightforward fix: one could add some logic into createNodeConfg() in pkg/nodebootstrap/al2023.go to return a basic NodeConfig that sets maxPods (omitting the cluster details as these would get set by EKS).

On the other hand, I may be missing a deeper understanding of why this restriction was added in the first place. If the maintainers believe this reasoning is sound, I'm happy to open a PR!

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