apiVersion: batch/v1
kind: Job
metadata:
  generateName: puzzle
spec:
  template:
    spec:
      containers:
      - name: main
        image: arbitrary-image
        env:
        - name: my_var
          valueFrom: <Contents of /mnt/my_var_value.txt>
        volumeMounts:
        - name: my-vol
          path: /mnt
      volumes:
      - name: my-vol
        persistentVolumeClaim:
          claimName: my-pvc