Unexpected behavior when using multiple contexts in kubeconfig

[oz123]

When using a config with multiple contexts, one might see a surprising message if there is no context set.
Let me demostrate:

$ k config get-contexts 
CURRENT   NAME               CLUSTER            AUTHINFO         NAMESPACE
          coldsweet          microk8s-cluster   admin-microk8s   coldsweet
          devops             devops-calico      admin            
          devops-cilium      devops-cilium      admin-cilium     
*         microk8s-context   microk8s-cluster   admin-microk8s   

Here, I have a context set. So kubectl get pods or any other command works fine.
If there is no current-context, kubectl says it can't connect to localhost (that's reasonable if you know k8s, more on that below).

sed -i '/current-context/d' ~/.kube/config
 $ k config get-contexts 
CURRENT   NAME               CLUSTER            AUTHINFO         NAMESPACE
          coldsweet          microk8s-cluster   admin-microk8s   coldsweet
          devops             devops-calico      admin            
          devops-cilium      devops-cilium      admin-cilium     
          microk8s-context   microk8s-cluster   admin-microk8s   
$ k get pods
The connection to the server localhost:8080 was refused - did you specify the right host or port?

What would you like to be added:
The above message is baffling if you encounter this for the first time. A better message would be something like this:

Mutliple contexts found but no context is set. Which cluster shall I use? Please set an active context

Why is this needed:
I give Kubernetes workshops, where students use multiple clusters. As we go through setting ~/.kube/confing for usage with multiple clusters, some students will rush to try stuff, and forget to set a context. This results in frustration and funny facial expressions staring at the screen. We explain that kubectl, uses localhost per default - and that older versions of kubernetes where not secured on localhost. A much better UI will be simply telling the user he didn't set up a context.

I'm willing to send a PR for improving this UI. This should not be hard to fix (I have already submitted code to k8s/k8s).

/sig usability

[oz123]

I believe this is #737 is related. The author solved his own problem. However, I am guess that's exactly the same behavior the workshop participants experience.

[oz123]

Validation of the configuration is done here:

https://github.com/kubernetes/kubernetes/blob/ba35704b510f918254c3ba826fb63608f6ed2dd6/staging/src/k8s.io/client-go/tools/clientcmd/validation.go#L152

The is already a validaor that checks that the context foo exists.

$ grep foo ~/.kube/config
current-context: foo
 $ k get pods
Error in configuration: context was not found for specified context: foo

To fix this issue, a validator that checks that the configuration has current-context set should be added.

[noahi]

Your suggested error content looks good to me. Is there a situation where localhost is desired?

[eddiezane]

/priority backlog

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