Kubernetes: Run container as non-root if there is no user specified

Question

How can I make every container run as non-root in Kubernetes?

Containers that do not specify a user, as in this example, and also do not specify a SecurityContext in the corresponding deployment, should still be able to be executed in the cluster - but without running as root. What options do you have here?

FROM debian:jessie
RUN apt-get update && apt-get install -y \
    git \
    python \
    vim
CMD ["echo", "hello world"]

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world
  namespace: mynamespace
spec:
  replicas: 1
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
        - image: hello-world
          name: hello-world

Answer 1

you can add Pod Security Policy to your cluster, there is an option (below) you can add to prevent any deployment from running without specifying a non-root user:

spec:
  runAsUser:
    rule: MustRunAsNonRoot

for more info about Pod Security Policy please go to this link: https://kubernetes.io/docs/concepts/security/pod-security-policy/