Support setting routeTables to virtualnetworkssubnets for AKS managed clusters

[staerion]

/kind feature

Describe the solution you'd like
This feature request applies to AKS managed clusters.

The capi azure provider can create virtualnetworks and subnets for AKS managed clusters. They can be configured under the field
AzureManagedControlPlane.spec.virtualNetwork.subnet. From this object you can configure the cidrBlock, name and optionally privateEndpoints and serviceEndpoints. In our use case we'd also like to configure a routeTable for the subnet. Currently this option is not support by capi azure provider.

Anything else you would like to add:
The aso controller itself does already have support for this option: https://azure.github.io/azure-service-operator/reference/network/v1api20201101/#network.azure.com/v1api20201101.VirtualNetworksSubnet

Environment:

• cluster-api-provider-azure version: v1.14.0
• Kubernetes version: (use kubectl version): 1.27.7
• OS (e.g. from /etc/os-release): Ubuntu 22.04.4 LTS

[jackfrancis]

cc @nojnhuh if you want to sanity check this scenario as available in your ASO AKS prototype

[nojnhuh]

@jackfrancis Yes, this kind of thing is possible with my prototype. Sorry @staerion I don't have anything to show for that yet, but keep your eyes on Slack and the PR queue in the coming weeks.

[staerion]

Great, thanksk for the heads up! We'll make sure to keep track of the slack channel and new releases.

[dtzar]

How would this work with CAPZ new ASO v2 API? @nojnhuh @nawazkh

[nojnhuh]

How would this work with CAPZ new ASO v2 API? @nojnhuh @nawazkh

You could add vnet and subnet resources to spec.resources of the AzureASOManagedCluster alongside the ResourceGroup and define them however you want:

cluster-api-provider-azure/templates/cluster-template-aks-aso.yaml

Line 48 in afde2c8

resources: