Kubernetes custom-columns select element from array

Question

I try to write a template, to list the names of my services as well as their external endpoints + ports. However, I don't find any examples or documentation how to select an element from an array, in this case port from the ports array.

I got that far:

 kubectl get service -o=custom-columns=NAME:.metadata.name,IP:.spec.clusterIP,PORT:.spec.ports

To give a more concrete example, this are my running services:

NAME                  CLUSTER-IP     EXTERNAL-IP      PORT(S)                               AGE
kafka-manager         10.3.242.200   146.148.20.235   9000:32619/TCP                        11h
spark-master          10.3.242.209   104.199.21.235   7077:30588/TCP                        11h

I wish to get:

NAME                  EXTERNAL-ENDPOINT     
kafka-manager         146.148.20.225:9000
spark-master          104.199.21.225:7077

Answer 1

TLDR

for an element that is list use * in square bracket.

So your query should look like this:

$ kubectl get service -n kube-system  -o=custom-columns=NAME:.metadata.name,IP:.spec.clusterIP,PORT:.spec.ports[*].targetPort
NAME                   IP           PORT
kube-dns               10.0.0.10    53,53
kubernetes-dashboard   10.0.0.250   9090

Notice the * in PORT:.spec.ports[*].targetPort.

Details:

So kubernetes is expecting a json-path-expr after header. The error I got when playing with expressions was following:

expected <header>:<json-path-expr>

So to iterate over all elements in a list instead of putting an index just use *.

Various other json-path expressions can be found here.