clusterctl fails with a nil pointer if no controlPlaneRef set in Cluster

[tobiasgiese]

What steps did you take and what happened?

Usually this should never happen. During a migration from a non-CAPI-managed cluster to a CAPI managed cluster I forgot to add the control plane reference in the Cluster object. This results in a nil pointer as the following code expects at least 1 control plane

cluster-api/cmd/clusterctl/client/tree/discovery.go

Lines 94 to 98 in 7edbaf0

	// Adds control plane
	controlPlane, err := external.Get(ctx, c, cluster.Spec.ControlPlaneRef, cluster.Namespace)
	if err == nil {
	addControlPlane(cluster, controlPlane, tree, options)
	}

To reproduce we can simply remove the controlPlaneRef from the Cluster and run a clusterctl describe cluster.

> kubectl patch cluster capi-quickstart --type='json' -p='[{"op": "remove", "path": "/spec/controlPlaneRef"}]'
cluster.cluster.x-k8s.io/capi-quickstart patched
> clusterctl describe cluster capi-quickstart -n default --grouping=false --show-conditions=all
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x96bdca]

goroutine 1 [running]:
k8s.io/apimachinery/pkg/apis/meta/v1/unstructured.(*Unstructured).GetAnnotations(0x1b4dd80?)
	k8s.io/[email protected]/pkg/apis/meta/v1/unstructured/unstructured.go:408 +0x4a
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.getAnnotation(...)
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/annotations.go:125
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.getBoolAnnotation({0x21628c0?, 0x0?}, {0x1e45082?, 0x28?})
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/annotations.go:130 +0x47
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.IsGroupingObject(...)
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/annotations.go:71
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.ObjectTree.Add({{0x21629d8, 0xc000703380}, {{0x7fff1fa45472, 0x3}, 0x0, 0x0, 0x0, 0x1, 0x0, 0x0}, ...}, ...)
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/tree.go:123 +0x346
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.Discovery.func1({0x21628c0?, 0x0?}, 0xc0001cd500)
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/discovery.go:107 +0x114
sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree.Discovery({0x21451d0, 0xc000126008}, {0x21502b8?, 0xc00035c700}, {0x7fff1fa45447, 0x7}, {0x7fff1fa45434, 0xf}, {{0x7fff1fa45472, 0x3}, ...})
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/tree/discovery.go:124 +0x6fd
sigs.k8s.io/cluster-api/cmd/clusterctl/client.(*clusterctlClient).DescribeCluster(0x0?, {{{0x0, 0x0}, {0x0, 0x0}}, {0x7fff1fa45447, 0x7}, {0x7fff1fa45434, 0xf}, {0x7fff1fa45472, ...}, ...})
	sigs.k8s.io/cluster-api/cmd/clusterctl/client/describe.go:91 +0x218
sigs.k8s.io/cluster-api/cmd/clusterctl/cmd.runDescribeCluster(0x0?, {0x7fff1fa45434, 0xf})
	sigs.k8s.io/cluster-api/cmd/clusterctl/cmd/describe_cluster.go:154 +0x1d8
sigs.k8s.io/cluster-api/cmd/clusterctl/cmd.glob..func6(0x3194820?, {0xc000800870?, 0x5?, 0x5?})
	sigs.k8s.io/cluster-api/cmd/clusterctl/cmd/describe_cluster.go:105 +0x2d
github.com/spf13/cobra.(*Command).execute(0x3194820, {0xc0008007d0, 0x5, 0x5})
	github.com/spf13/[email protected]/command.go:916 +0x862
github.com/spf13/cobra.(*Command).ExecuteC(0x3197340)
	github.com/spf13/[email protected]/command.go:1044 +0x3bd
github.com/spf13/cobra.(*Command).Execute(...)
	github.com/spf13/[email protected]/command.go:968
sigs.k8s.io/cluster-api/cmd/clusterctl/cmd.Execute()
	sigs.k8s.io/cluster-api/cmd/clusterctl/cmd/root.go:105 +0x25
main.main()
	sigs.k8s.io/cluster-api/cmd/clusterctl/main.go:27 +0x17

What did you expect to happen?

At least an error that no control plane reference is set. Alternatively, no valid KCP can be displayed via clusterctl describe cluster.

Cluster API version

main branch

Kubernetes version

No response

Anything else you would like to add?

/

Label(s) to be applied

/kind bug
One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.

[killianmuldoon]

/triage accepted

We should in all cases try to catch nil-pointers IMO.

[aniruddha2000]

would like to work
/assign

[tobiasgiese]

would like to work /assign

Sorry, didn't saw that 😞 was already implementing the fix during issue creation

[aniruddha2000]

No worries! I would definitely like to see the solution once it's there

[tobiasgiese]

No worries! I would definitely like to see the solution once it's there

It's already there, see #8604

/assign