If you followed the previous pages for the Kubernetes resource, you may have gotten the idea that the subcommand delete is used to remove resources. It is workable in the case of removing a Namespace. At the same time, if we try to delete a Namespace, the resources under it will be removed, as well:

// first, go ahead to remove the Namespace "my-namespace"
$ kubectl delete ns my-namespace
namespace "my-namespace" deleted
// check the Deployment again, the exited "my-nginx" is terminated
$ kubectl get deployment
No resources found.

// while trying to create anything, the error message showing the default Namespace is not existed
$ kubectl run my-alpine --image=alpine
Error from server (NotFound): namespaces "my-namespace" not found

To solve this issue, you may attach another Namespace to the current context, or just change your current context to the previous one:

// first solution: use set-context to update the Namespace
// here we just leave Namespace empty, which means to use default Namespace
$ kubectl config set-context my-context --namespace=""
Context "my-context" modified.

// second solution: switch current context to another context
// in this case, it is kubeadm environment
$ kubectl config use-context kubernetes-admin@kubernetes
Switched to context "kubernetes-admin@kubernetes".