apiVersion: kyverno.io/v1alpha1
kind: ClusterPolicy
metadata:
  name: validate-readonly-rootfilesystem
  annotations:
    policies.kyverno.io/category: Security Context
    policies.kyverno.io/description: A read-only root file system helps to enforce an immutable 
      infrastructure strategy; the container only needs to write on the mounted volume that p
      ersists the state. An immutable root filesystem can also prevent malicious binaries from 
      writing to the host system.
spec:
  rules:
  - name: validate-readonly-rootfilesystem
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Container require read-only rootfilesystem"
      pattern:
        spec:
          containers:
          - securityContext:
              readOnlyRootFilesystem: true