How to format the output in Kubernetes?

Question

I want to get specific output for a command like getting the nodeports and loadbalancer of a service. How do I do that?

What have you tried so far (that didn't work or was showing undesired output)? Hav you tried `kubectl describe svc your-service-name`? — deHaar, Jun 10 '21 at 06:40

score 2 · Accepted Answer · answered Jun 10 '21 at 08:13

The question is pretty lacking on what exactly wants to be retrieved from Kubernetes but I think I can provide a good baseline.

When you use Kubernetes, you are most probably using kubectl to interact with kubeapi-server.

Some of the commands you can use to retrieve the information from the cluster:

$ kubectl get RESOURCE --namespace NAMESPACE RESOURCE_NAME
$ kubectl describe RESOURCE --namespace NAMESPACE RESOURCE_NAME

Example:

Let's assume that you have a Service of type LoadBalancer (I've redacted some output to be more readable):

$ kubectl get service nginx -o yaml

apiVersion: v1
kind: Service
metadata:
  name: nginx
  namespace: default
spec:
  clusterIP: 10.2.151.123
  externalTrafficPolicy: Cluster
  ports:
  - nodePort: 30531
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx
  sessionAffinity: None
  type: LoadBalancer
status:
  loadBalancer:
    ingress:
    - ip: A.B.C.D

Getting a nodePort from this output could be done like this:

kubectl get svc nginx -o jsonpath='{.spec.ports[].nodePort}'

Getting a loadBalancer IP from this output could be done like this:

kubectl get svc nginx -o jsonpath="{.status.loadBalancer.ingress[0].ip}"

A.B.C.D

You can also use kubectl with custom-columns:

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

NAME         IP
kubernetes   10.2.0.1
nginx        10.2.151.123

There are a lot of possible ways to retrieve data with kubectl which you can read more by following the:

kubectl get --help:

-o, --output='': Output format. One of: json|yaml|wide|name|custom-columns=...|custom-columns-file=...|go-template=...|go-template-file=...|jsonpath=...|jsonpath-file=... See custom columns, golang template and jsonpath template.

Kubernetes.io: Docs: Reference: Kubectl: Cheatsheet: Formatting output

Additional resources:

Kubernetes.io: Docs: Reference: Kubectl: Overview
Github.com: Kubernetes client: Python - if you would like to retrieve this information with Python
Stackoverflow.com: Answer: How to parse kubectl describe output and get the required field value

Thanks ! this was exactly what i wanted – Anvay Jun 13 '21 at 07:22 — Anvay, Jun 13 '21 at 07:22

score 0 · Answer 2 · answered Jun 10 '21 at 08:19

If you want to extract just single values, perhaps as part of scripts, then what you are searching for is -ojsonpath such as this example:

kubectl get svc service-name -ojsonpath='{.spec.ports[0].port}'

which will extract jus the value of the first port listed into the service specs.

docs - https://kubernetes.io/docs/reference/kubectl/jsonpath/

If you want to extract the whole definition of an object, such as a service, then what you are searching for is -oyaml such as this example:

kubectl get svc service-name -oyaml

which will output the whole service definition, all in yaml format.

If you want to get a more user-friendly description of a resource, such as a service, then you are searching for a describe command, such as this example:

kubectl describe svc service-name

docs - https://kubernetes.io/docs/reference/kubectl/overview/#output-options

How to format the output in Kubernetes?

2 Answers2

Example:

Linked