"kubectl --template". How can I understand it?

I can't catch up what is the difference between kubectl.....-o jsonpath='{...}' and kubectl....--template='{{...}}'

Are they both just for retrieving data? I know well about the jsonpath flag. But couldn't understand the template flag. Is there a difference?

I think https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands here are some descriptions. But I can't understand it. Could you please explain more about it?

Solution

1. kubectl ... -o jsonpath='{...}'

This option allows you to extract specific data from the JSON representation of Kubernetes resources.
You provide a JSONPath expression enclosed in single quotes ('...') after the -o jsonpath= flag.
JSONPath is a query language for JSON data that lets you specify a path to navigate through the JSON structure and extract specific values.
It is primarily used for filtering and extracting data, making it more suitable for cases where you need fine-grained control over what data to retrieve.

Example:

kubectl get pod my-pod -o jsonpath='{.status.phase}'

This command retrieves the phase field from the JSON representation of the my-pod resource.

2. kubectl ... --template='{{...}}'

This option allows you to use Go templates to format the output of kubectl. You provide a Go template enclosed in double curly braces ({{...}}) after the --template= flag.
Go templates are a more powerful and flexible way to format output. They allow you to manipulate and format data in various ways, including conditional statements and loops.
It's not limited to extracting data but can also perform transformations on the data and create custom output formats.

Example:

kubectl get pod my-pod --template='{{.metadata.name}} is in {{.status.phase}} phase'

This command formats the output to display the pod's name and phase in a custom format.

In summary, both jsonpath and template options in kubectl are used for retrieving data from Kubernetes resources, but they serve different purposes:

jsonpath is focused on extracting specific data using a JSONPath expression, which is useful for simple data extraction.
template is more versatile and allows you to format and manipulate the output using Go templates, making it suitable for complex formatting and transformations.

The choice between the two depends on your specific use case and whether you need simple data extraction or more advanced formatting and processing of the output.