Kubernetes Downward API Concepts

External

• https://kubernetes.io/docs/concepts/storage/volumes/#downwardapi
• https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/

Internal

• Kubernetes Concepts
• Kubernetes Storage Concepts

Overview

Kubernetes is exposing pod information to the containers running inside the pod through files, which are projected in the container by a mechanism known as the Downward API.

Example

This is how the pod name and namespace can be projected to be available to containers running inside the pod.

Declare a "downwardAPI" volume, conventionally named "podinfo" and mount it in the pod:

apiVersion: v1
kind: Pod
metadata:
  name: loop
spec:
  containers:
  - name: loop
    image: docker.io/ovidiufeodorov/loop:latest
    volumeMounts:
      - name: "podinfo"
        mountPath: "/etc/podinfo"
  volumes:
  - name: podinfo
    downwardAPI:
      items:
        - path: "metadata/name"
          fieldRef:
            fieldPath: "metadata.name"

Note that individual downwardAPI items can declare a hierarchical path - the directories will be created automatically.