Simple example of a Deployment with an env based on the namespace

README.md

Build environment variables on the values of other variables

https://kubernetes.io/docs/tasks/inject-data-application/define-interdependent-environment-variables/

Expose introspection information to pod

https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/

downward-test.yaml

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: downward-test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        envFrom:
          - configMapRef:
              name: my-configmap
        env:
        - name: DAT_NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace
        - name: TEST_URL
          value: "https://$(DAT_NAMESPACE)"