Passing Metadata Fields to Arguments in Kubernetes Yaml Files

• 18/4/2023
• 2-minute read

Passing metadata fields like metadata.name or metadata.namespace to the arguments field in Kubernetes YAML files is a powerful way to dynamically configure your containers and pods. This can be especially useful when you need to pass information about the pod or the environment to your application code.

The fieldRef syntax allows you to reference a specific field in the Kubernetes API object using the fieldPath attribute. This attribute takes a string that describes the path to the field in the object, using dot notation to separate nested fields.

Here’s an example of how to pass the metadata.name field to the arguments field in a Kubernetes YAML file:

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
    - name: my-container
      image: my-image
      command: ["/bin/sh"]
      args: ["-c", "echo My name is $(MY_POD_NAME)"]
      env:
        - name: MY_POD_NAME
          valueFrom:
            fieldRef:
              fieldPath: metadata.name

In this example, I’ve set the value of the MY_POD_NAME environment variable to the value of the metadata.name field using the fieldRef syntax.

The env field in the container configuration specifies that the value of the MY_POD_NAME environment variable should be set using the fieldRef syntax. The fieldPath attribute specifies that the value of the environment variable should be set to the value of the metadata.name field.

Note that the metadata.name field is only available when the pod is running. If you need to set the value of the MY_POD_NAME environment variable before the pod starts up, you will need to use a different approach, such as using a Kubernetes init container to set the value of the environment variable.

Using the fieldRef syntax to pass metadata fields to the arguments field can be a powerful way to dynamically configure your containers and pods. With this approach, you can easily pass information about the pod or the environment to your application code, without having to hardcode the values in your YAML files.

Below, you can find another example:

apiVersion: k6.io/v1alpha1
kind: K6
metadata:
  name: k6-ot-load-tests
  namespace: ot-load-tests
spec:
  parallelism: 3
  script:
    configMap:
      name: "ot-load-test-scripts"
      file: "scenario_get-watchlist.js"
  arguments:
    - -e
    - ENVIRONMENT=DEV
    - -e
    - PARALLELISM=3
    - -e
    - POD_NAME=$(POD_NAME)
  runner:
    env:
      - name: POD_NAME
        valueFrom:
          fieldRef:
            fieldPath: metadata.name