Automatically change registry in pod definition

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In this post I will show you how you can automatically change the registry part in deployed pods in Kubernetes.

Parts of the K8S Security Lab series

Container Runetime Security
Advanced Kernel Security
Network Security
Secure Kubernetes Install
User Security
Image Security
  • Part1: Image security Admission Controller
  • Part2: Image security Admission Controller V2
  • Part3: Image security Admission Controller V3
  • Part4: Continuous Image security
  • Part5: trivy-operator 1.0
  • Part6: trivy-operator 2.1: Trivy-operator is now an Admisssion controller too!!!
  • Part7: trivy-operator 2.2: Patch release for Admisssion controller
  • Part8: trivy-operator 2.3: Patch release for Admisssion controller
  • Part8: trivy-operator 2.4: Patch release for Admisssion controller
  • Part8: trivy-operator 2.5: Patch release for Admisssion controller
  • Part9_ Image Signature Verification with Connaisseur
  • Part10: Image Signature Verification with Connaisseur 2.0
  • Part11: Image Signature Verification with Kyverno
  • Part12: How to use imagePullSecrets cluster-wide??
  • Part13: Automatically change registry in pod definition
  • Part14: ArgoCD auto image updater
    Pod Security
    Secret Security
    Monitoring and Observability
    Backup

    ImageSwap Mutating Admission Controller for Kubernetes

    The ImageSwap webhook enables you to define one or more mappings to automatically swap image definitions within Kubernetes Pods with a different registry.

    Install ImageSwap:

    $ kubectl apply -f https://raw.githubusercontent.com/phenixblue/imageswap-webhook/v1.4.2/deploy/install.yaml

    For swapping configuration ImageSwap use a configmap to define what image should change to what:

    apiVersion: v1
data:
  maps: |
    default:registry.example.com
    #gcr.io: # This is a comment
    gitlab.com:registry.example.com/gitlab
    noswap_wildcards:example.com    
kind: ConfigMap
metadata:
  creationTimestamp: null
  name: imageswap-maps
  namespace: imageswap-system

    Example MAPS Configs:

    Disable image swapping for all registries EXCEPT gcr.io

    default:
gcr.io:harbor.internal.example.com

    Enable image swapping for all registries except gcr.io

    With this, all images will be swapped except those that already match the harbor.internal.example.com pattern

    default:harbor.internal.example.com
noswap_wildcards:harbor.internal.example.com

    Test ImageSwap

    $ kubectl create ns test1
$ kubectl label ns test1 k8s.twr.io/imageswap=enabled

    Then deploy a pod:

    kubectl create deployment unsigned-my \
--image=docker.io/devopstales/testimage:unsigned

    ImageSwap can be disabled on a per workload level by adding the k8s.twr.io/imageswap label with a value of disabled to the pod template.

    Kyverno

    Here is an example of a Kyverno policy that validates that images are only pulled from an allowed list of image registries (based on wildcard patterns):

    apiVersion : kyverno.io/v1alpha1
kind: Policy
metadata:
  name: check-registries
spec:
  rules:
  - name: check-registries
    resource:
      kinds:
      - Deployment
      - StatefulSet
    validate:
      message: "Registry is not allowed"
      pattern:
        spec:
          template:
            spec:
              containers:
              - name: "*"
                # Check allowed registries
                image: "*/nirmata/* | https://private.registry.io/*"

    Rather than blocking Pods which come from outside registries, it is also possible to mutate them so the pulls are directed to approved registries.

    apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: replace-image-registry
  annotations:
    policies.kyverno.io/title: Replace Image Registry
    policies.kyverno.io/category: Sample
    policies.kyverno.io/severity: medium
    policies.kyverno.io/subject: Pod
    policies.kyverno.io/minversion: 1.3.6
    policies.kyverno.io/description: >-
      Rather than blocking Pods which come from outside registries,
      it is also possible to mutate them so the pulls are directed to
      approved registries. In some cases, those registries may function as
      pull-through proxies and can fetch the image if not cached.
      This policy policy mutates all images either
      in the form 'image:tag' or 'registry.corp.com/image:tag' to be prefaced
      with `myregistry.corp.com/`.            
spec:
  background: false
  rules:
    - name: replace-image-registry
      match:
        resources:
          kinds:
          - Pod
      mutate:
        patchStrategicMerge:
          spec:
            containers:
            - (name): "*"
              image: |-
                                                                {{ regex_replace_all('^[^/]+', '{{@}}', 'myregistry.corp.com') }}