ORing label selectors with kubectl

2021/04/05 1-minute read

Let’s say you want, using the kubectl, to get all pods with label tier=backend OR tier=frontend.

Did you know you could do the following?

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kubectl get pods -l 'tier in (backend, frontend)'

We at $WORK did not.

It’s actually even more powerful, you can use notin, you can combine with , to perform AND. I recommend reading the docs for more examples.

Also, if you are at the exploration phase, don’t forget to pass --show-labels to have a understanding of the existing labels.

Or, if you want to reduce the clutter and only display the fields you are interested in:

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kubectl get pods -l 'tier in (backend, frontend)' \
  -o custom-columns=name:.metadata.name,labels:.metadata.labels

NAME                           LABELS
admin-699855c9c6-s8fc6         map[app:admin tier:frontend]
authserver-646864ddf8-jt2f6    map[app:authserver tier:backend]
client-79678bf8c-qgp8j         map[app:client tier:frontend]
(...)

Here’s a confession: sometimes I give up and just pipe to classic unix tools:

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kubectl get pods -l 'tier in (backend, frontend)' --show-labels | \
  awk '{ print $1, $6 }' | column -t

> NAME                        LABELS
admin-699855c9c6-s8fc6        app=admin,tier=frontend
authserver-646864ddf8-jt2f6   app=authserver,tier=backend
client-79678bf8c-qgp8j        app=client,tier=frontend
(...)

Links

Labels and Selectors | Kubernetes