Kubernetes Explained Simply: Data Extraction With JSON Path [Part 8]

kubectl

can pull a lot of data about our deployments and pod. Most of the time, we humans are the recipients of that information, and

kubectl

obliges by nicely formatting things in pretty tables.

$ kubectl get pods
NAME                        READY   STATUS    RESTARTS   AGE
frontend-64d9f4f776-9fzp8   3/3     Running   0          14s
frontend-64d9f4f776-flx58   3/3     Running   0          15s
frontend-64d9f4f776-lftdc   3/3     Running   0          15s
frontend-64d9f4f776-mrhq6   3/3     Running   0          15s

Ah yes, I see the pod is now called "... FIXME ..."

In my experience, the very next command that I run needs that auto-generated Pod ID, something like

kubectl logs

kubectl exec

. The first couple of times, you'll use the pasteboard – highlight the pod name with your mouse,

Cmd-C

, and you're off to the races. By the third, fourth, or fiftieth time, however, you'll be wishing for a better way.

This is UNIX, right? World-famous for its text processing capabilities? We got this covered.

$ kubectl get pods
$ kubectl get pods | awk '{print $1}'
$ kubectl get pods | awk '{print $1}' | grep -v ^NAME

Well, it does work, even if it is a bit awkward, and a lot to type.

kubectl

has lots of different output formats at its disposal; the default one just happens to be such a good fit for human eyes that we don't always go looking for others. We can change the output format via the

-o

flag. For example, we can dump all of the pods in JSON format, and then use

jq

to parse through it:

$ kubectl get pods -o json | \
      jq -r '.items[0].metadata.name'
frontend-64d9f4f776-9fzp8

What happens if we don't have

jq

available to us? This may surprise you, what with this being a blog post about

kubectl

tricks and all, but

kubectl

can do this natively...

It's called JSON Path, and it essentially lets you embed simple

jq

scripts into your

kubectl

call, directly:

$ kubectl get pods -o jsonpath='{.items[0].metadata.name}'
frontend-64d9f4f776-9fzp8

(Just remember to enclose the variable reference in balanced curly braces.)

JSON Path has its fair share of fanciness, including filters. For example, if you have a pod with lots of constituent containers, you can extract information about a subset like this:

$ kubectl get pods -o jsonpath='{.items[0].spec.containers[?(@.image == "redis")].name}'
kv-store
session-cache

Here we're identifying which containers in our pod are running the upstream

redis

image. Neat!

Also published here.