How can get READY, STATUS, RESTARTS, AGE,etc in kubectl as custom-columns?

Question

I just want to list pods with their .status.podIP as an extra column. It seems that as soon as I specify -o=custom-colums= the default columns NAME, READY, STATUS, RESTARTS, AGE will disappear.

The closest I was able to get is

kubectl get pod -o wide -o=custom-columns="NAME:.metadata.name,STATUS:.status.phase,RESTARTS:.status.containerStatuses[0].restartCount,PODIP:.status.podIP"

but that is not really equivalent to the the default columns in the following way:

• READY: I don't know how to get the default output (which looks like 2/2 or 0/1 by using custom columns
• STATUS: In the default behaviour STATUS, can be Running, Failed, Evicted, but .status.phase will never be Evicted. It seems that the default STATUS is a combination of .status.phase and .status.reason. Is there a way to say show .status.phase if it's Running but if not show .status.reason?
• RESTARTS: This only shows the restarts of the first container in the pod (I guess the sum of all containers would be the correct one)
• AGE: Again I don't know how to get the age of the pod using custom-columns

Does anybody know the definitions of the default columns in custom-columns syntax?

Answer 1

I checked the differences between in API requests between the kubectl get pods and kubectl -o custom columns:

• With aggregation:

curl -k -v -XGET -H Accept: application/json;as=Table;v=v1;g=meta.k8s.io,application/json;as=Table;v=v1beta1;g=meta.k8s.io,application/json -H User-Agent: kubectl/v1.18.8 (linux/amd64) kubernetes/9f2892a http://127.0.0.1:8001/api/v1/namespaces/default/pods?limit=500 

• Without aggregation:

curl -k -v -XGET -H Accept: 
application/json -H User-Agent: kubectl/v1.18.8 (linux/amd64) kubernetes/9f2892a http://127.0.0.1:8001/api/v1/namespaces/default/pods?limit=500

So you will notice that when -o custom columns is used, kubectl gets PodList instead of Table in response body. Podlist does not have that aggregated data, so to my understanding it is not possible to get the same output with kubectl pods using custom-column.

Here's a code snippet responsible for the output that you desire. Possible solution would be to fork the client and customize it to your own needs since as you already might notice this output requires some custom logic. Another possible solution would be to use one of the Kubernetes api client libraries. Lastly you may want to try extend kubectl functionalities with kubectl plugins.