Multiple subnet creation fails when zone is not specified

[Amulyam24]

/kind bug
/area provider/ibmcloud

What steps did you take and what happened:
If zone it not specified while creating multiple subnets, second subnet creation will fail as the default address prefix is already assigned to the first subnet.
Spec:

apiVersion: infrastructure.cluster.x-k8s.io/v1beta2
kind: IBMPowerVSCluster
metadata:
  annotations:
    powervs.cluster.x-k8s.io/create-infra: "true"
  labels:
    cluster.x-k8s.io/cluster-name: capi-test-amulya
  name: capi-test-amulya
  namespace: default
spec:
  loadBalancers:
  - name: capi-test-amulya-loadbalancer
  - name: capi-test-amulya-loadbalancer-1
  resourceGroup:
    name: ibm-hypershift-dev
  serviceInstance:
    name: capi-test-amulya-serviceInstance
  transitGateway:
    name: capi-test-amulya-transitgateway
  vpc:
    name: capi-test-amulya-vpc
    region: eu-es
  vpcSubnets:
  - name: capi-test-amulya-vpcsubnet
  - name: capi-test-amulya-vpcsubnet-1
  zone: mad02

Creation fails with

"error creating vpc subnet" err="Subnet CIDR 10.251.0.0/18 conflicts with existing subnet: 02w7-c247a3e9-c9d0-4717-a878-96edd68059c4

What did you expect to happen:
While creating multiple subnets, if subnet zone is missing from spec, don't proceed and instead throw an error.

Anything else you would like to add:
We can add a check to validate the spec before proceeding with cluster creation.

Environment:

• Cluster-api version:
• Minikube/KIND version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[Amulyam24]

/good-first-issue

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[mkumatag]

but how are we handling that for the first subnet when user didn't supply the zone?

While creating multiple subnets, if subnet zone is missing from spec, don't proceed and instead throw an error.

[Amulyam24]

but how are we handling that for the first subnet when user didn't supply the zone?

While creating multiple subnets, if subnet zone is missing from spec, don't proceed and instead throw an error.

We are fetching the zone from PowerVS zone - https://github.com/kubernetes-sigs/cluster-api-provider-ibmcloud/blob/main/cloud/scope/powervs_cluster.go#L1113-L1130

[Shilpa-Gokul]

@Amulyam24 I would like to work on this issue

[Shilpa-Gokul]

/assign @Shilpa-Gokul

[mkumatag]

but how are we handling that for the first subnet when user didn't supply the zone?

While creating multiple subnets, if subnet zone is missing from spec, don't proceed and instead throw an error.

We are fetching the zone from PowerVS zone - https://github.com/kubernetes-sigs/cluster-api-provider-ibmcloud/blob/main/cloud/scope/powervs_cluster.go#L1113-L1130

There is logic written to use always the first one here -

// TODO(karthik-k-n): Decide on using all zones or using one zone
		if len(vpcZones) == 0 {
			return nil, fmt.Errorf("error getting vpc zones error: %v", err)
		}
		zone = vpcZones[0]

wondering if we need a logic to use the subsequent vpc zone for the next subnet?!

[Amulyam24]

but how are we handling that for the first subnet when user didn't supply the zone?

While creating multiple subnets, if subnet zone is missing from spec, don't proceed and instead throw an error.

We are fetching the zone from PowerVS zone - https://github.com/kubernetes-sigs/cluster-api-provider-ibmcloud/blob/main/cloud/scope/powervs_cluster.go#L1113-L1130

There is logic written to use always the first one here -

// TODO(karthik-k-n): Decide on using all zones or using one zone
		if len(vpcZones) == 0 {
			return nil, fmt.Errorf("error getting vpc zones error: %v", err)
		}
		zone = vpcZones[0]

wondering if we need a logic to use the subsequent vpc zone for the next subnet?!

yes, we can try that out.

[Karthik-K-N]

We had a discussion regarding this issue and couple things decided are as follows

1. Continue with existing flow when no subnets are set that is create subnet in each available zone for VPC.

2. For selecting subnet CIDR, Use the field AddressPrefix.HasSubnets to identify whether to use the CIDR for subnet

addressPrefixCollection, _, err := vpcService.ListVPCAddressPrefixes(options)

addressPrefixCollection.AddressPrefixes[].HasSubnets

3. For now allow only one subnet per VPC zone, If user specifies more subnets error out.

[Karthik-K-N]

Also we can avoid fetching CIDR and use total ip while creating subnet, For more reference see vpc subnet code and discussion