I'd like to be able to override the subnet default hostname type for EC2 instances created by Karpenter

@stevehipwell Is this a launch template configuration setting?

@jonathan-innis I think it is. However the general docs which says that you can use the resource name for hostname in all scenarios is contradicted in other documents. I think this is still useful if you need an IPv6 enabled subnet, but less compelling.

I can confirm that it's a launch template configuration setting. I'm not sure what docs you're referring to @stevehipwell, but I just tried launching an EC2 instance in an IPv4-only VPC with the "resource name" hostname type and it definitely configured the hostname accordingly. I'd love to see this feature!

EDIT: my read of the launch template design doc suggests that we might not want a control knob for this. If that's the case, then I argue that we should always configure the launch template to use the "resource name" configuration setting, because the default configuration setting of "IP Name" is referred to as a legacy naming scheme in the docs. As an added bonus, it sounds like this would make kops and eks more consistent?

Happy to try my hand at a PR for this if I can get some guidance on making this behavior always true vs making it opt-in/configurable.

Tried to use this with karpenter
https://awslabs.github.io/amazon-eks-ami/nodeadm/doc/examples/#using-instance-id-as-node-name-experimental
Unfortunately kubelet then cannot register in cluster:

Sep 20 09:36:25 ip-10-20-7-154.eu-north-1.compute.internal kubelet[2119]: E0920 09:36:25.288492    2119 kubelet_node_status.go:92] "Unable to register node with API server" err="nodes \"i-0018a651259c57f2d\" is forbidden: node \"ip-10-20-7-154.eu-north-1.compute.internal\" is not allowed to modify node \"i-0018a651259c57f2d\"" node="i-0018a651259c57f2d"

Update: it does not work with "EKS API" auth in EKS. Only works with "ConfigMap" auth, exactly as written in docs. Node name in k8s and EC2 "Name" tag becomes "i-xxx". But actual hostname of OS still is "ip-x-x-x-x"