Kubernetes Downward API

Sometimes you want to expose information about the constraints the container is running without duplicating values or have the application reach out to the Kubernetes API.

The Downward API helps with this problem where you can inject pod information to the container via env variables.

For example, let’s imagine we want to set the GOMAXPROCS depending on the CPU limit:

apiVersion: v1
kind: Pod
metadata:
  name: my-app
spec:
  containers:
    - name: my-app
      image: golang
      resources:
        requests:
          memory: "32Mi"
          cpu: "125m"
        limits:
          memory: "64Mi"
          cpu: "250m"
      env:
        - name: GOMAXPROCS
          valueFrom:
            resourceFieldRef:
              containerName: my-app
              resource: limits.cpu

The example above would sets GOMAXPROCS to 1 because resourceFieldRef gets the limits.cpu for that container as shown in the docs