How to format the output in Kubernetes? - 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?

Answer 1

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}'
30531
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

Answer 2

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