check nil cluster is provided

[jichenjc]

/kind bug

What steps did you take and what happened:
[A clear and concise description of what the bug is.]
At the moment, cluster-api-provider-openstack panics with a nil pointer if there is no cluster
We might want to make sure to return an error if a nil cluster is provided.

What did you expect to happen:

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

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

[jichenjc]

/assign

[jichenjc]

@chrigl can you take a look whether I am finding the right place? I think during review on update cluster-api version PR,
this is the place you talked about ? if cluster is nil, then we will panice
https://github.com/kubernetes-sigs/cluster-api-provider-openstack/blob/master/pkg/cloud/openstack/cluster/actuator.go#L31
seems aws has same issue?
https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/master/pkg/cloud/aws/actuators/cluster/actuator.go#L61

or I am in wrong place ?

[chrigl]

@jichenjc Yes this is one place. Other places are in machine/actuator.go

• in Create: https://github.com/kubernetes-sigs/cluster-api-provider-openstack/blob/master/pkg/cloud/openstack/machine/actuator.go#L137
• and Update: https://github.com/kubernetes-sigs/cluster-api-provider-openstack/blob/master/pkg/cloud/openstack/machine/actuator.go#L276

Maybe just doing a check at the top of all of the machine.Actuator functions, to prevent further accident panics.

And also yes. The aws code also looks like to have this problem.