Updating Cluster network configuration for single stack to dual-stack upgrades

[christianang]

User Story

As an operator I would like to update the cluster network configuration for an existing Cluster resource for upgrading a single stack Cluster to a dual-stack Cluster.

Detailed Description

I'd like to be able to add the cidr range for an additional IP family to spec.clusterNetwork.pods.cidrBlocks and spec.clusterNetwork.services.cidrBlocks e.g If I have a single stack IPv4 cluster with IPv4 cidr ranges I'd like to be able to add IPv6 cidr ranges to the cidrBlocks to upgrade my cluster to a dual-stack cluster.

Updating the cidrBlocks on a Cluster needs to be able to reconcile the KubeadmControlPlane with the additional CIDRs. Right now it seems like the KubeadmControlPlane disallows changes to the clusterConfiguation.networking.{serviceSubnet,podSubnet} and updating the cidrBlocks on a Cluster also does not affect the KubeadmControlPlane.

Anything else you would like to add:

• There may be some complexity to orchestrating this because PodCIDRs are cached on a node so you have to drain, delete, re-init the node to change PodCIDRs (from how to change PODcidr on specifiec nodes Kubernetes kubernetes/kubernetes#87150 (comment))

/kind feature

[fabriziopandini]

We discussed this in the 20th July office hours and I'm reporting my take from the discussion (feel free to discuss)

• unblocking the webhook is the easiest part, but we should understand what this operation entails at infrastructure level and/or at node level
• given ^^ we should evaluate if it is worth to go down this path or it will be simpler to create a new cluster and migrate workloads

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/lifecycle stale

[k8s-triage-robot]

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/lifecycle rotten

[fabriziopandini]

It is not clear how to address this use case and if there are contributors willing to invest in this effort.
but let's keep this around at least till the bot closes it
/triage accepted

[fabriziopandini]

/help

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[fabriziopandini]

(doing some cleanup on old issues without updates)
/close
unfortunately, no one is picking up the task. the thread will remain available for future reference