If you want to pull from a docker registry you need to docker login first.

Image Digest

List all container registries for all containers running in a cluster

root@scw-k8s:~# k get pods -A -ojsonpath='{range .items[*]}{.spec.containers[*].image}{"\n"}{end}'
nginx
k8s.gcr.io/coredns/coredns:v1.8.6
k8s.gcr.io/coredns/coredns:v1.8.6
k8s.gcr.io/etcd:3.5.1-0
k8s.gcr.io/kube-apiserver:v1.23.6
k8s.gcr.io/kube-controller-manager:v1.23.6
k8s.gcr.io/kube-proxy:v1.23.6
k8s.gcr.io/kube-scheduler:v1.23.6
docker.io/weaveworks/weave-kube:2.8.1 docker.io/weaveworks/weave-npc:2.8.1

More precisely, we are interested in digest, which references an exact image version (which is much better than using tags)

root@scw-k8s:~# k get pods -A -ojsonpath='{range .items[*]}{.status.containerStatuses[*].imageID}{"\n"}{end}'

k8s.gcr.io/coredns/coredns@sha256:5b6ec0d6de9baaf3e92d0f66cd96a25b9edbce8716f5f15dcd1a616b3abd590e
k8s.gcr.io/coredns/coredns@sha256:5b6ec0d6de9baaf3e92d0f66cd96a25b9edbce8716f5f15dcd1a616b3abd590e
k8s.gcr.io/etcd@sha256:64b9ea357325d5db9f8a723dcf503b5a449177b17ac87d69481e126bb724c263
k8s.gcr.io/kube-apiserver@sha256:0cd8c0bed8d89d914ee5df41e8a40112fb0a28804429c7964296abedc94da9f1
k8s.gcr.io/kube-controller-manager@sha256:df94796b78d2285ffe6b231c2b39d25034dde8814de2f75d953a827e77fe6adf
k8s.gcr.io/kube-proxy@sha256:cc007fb495f362f18c74e6f5552060c6785ca2b802a5067251de55c7cc880741
k8s.gcr.io/kube-scheduler@sha256:02b4e994459efa49c3e2392733e269893e23d4ac46e92e94107652963caae78b
docker.io/weaveworks/weave-kube@sha256:d797338e7beb17222e10757b71400d8471bdbd9be13b5da38ce2ebf597fb4e63 docker.io/weaveworks/weave-npc@sha256:38d3e30a97a2260558f8deb0fc4c079442f7347f27c86660dbfc8ca91674f14c
r

Secure container registries

Install OPA Gatekeeper: kubectl create -f https://raw.githubusercontent.com/killer-sh/cks-course-environment/master/course-content/opa/gatekeeper.yaml

Create OPA template to restrict allowed container registries

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8strustedimages
spec:
  crd:
    spec:
      names:
        kind: K8sTrustedImages
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8strustedimages
        violation[{"msg": msg}] {
          image := input.review.object.spec.containers[_].image
          not startswith(image, "docker.io/")
          not startswith(image, "k8s.gcr.io/")
          msg := "not trusted image!"
        }

Specify for what kind of resources the K8sTrustedImages OPA constraint template will be applied (e.g. pods)

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sTrustedImages
metadata:
  name: pod-trusted-images
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]

And now test it!

# will not work :)
controlplane $ k run podx --image=nginx
Error from server ([pod-trusted-images] not trusted image!): admission webhook "validation.gatekeeper.sh" denied the request: [pod-trusted-images] not trusted image!


# how about this
controlplane $ k run podx --image=docker.io/nginx
pod/podx created

Deploy webhook service (en external service) which will validate image policy so called: ImagePolicyWebhook

Configure kube-apiserver server first (will not work until you do some further configuration)

vim /etc/kubernetes/manifests/kube-apiserver
...
    - --enable-admission-plugins=NodeRestriction,ImagePolicyWebhook
    - --admission-control-config-file=/etc/kubernetes/admission/admission_config.yaml
...
    - mountPath: /etc/kubernetes/admission
      name: k8s-admission
      readOnly: true 

...
  - hostPath:
      path: /etc/kubernetes/admission
      type: DirectoryOrCreate
    name: k8s-admission
...

:wq

Configure admission_config.yaml the one which is specified in kube-apiserver under --admission-control-config-file

cat admission_config.yaml
apiVersion: apiserver.config.k8s.io/v1
kind: AdmissionConfiguration
plugins:
  - name: ImagePolicyWebhook
    configuration:
      imagePolicy:
        kubeConfigFile: /etc/kubernetes/admission/kubeconf
        allowTTL: 50
        denyTTL: 50
        retryBackoff: 500
        defaultAllow: false

Configure /etc/kubernetes/admission/kubeconf everything what is inside

cat /etc/kubernetes/admission/kubeconf
apiVersion: v1
kind: Config

# clusters refers to the remote service.
clusters:
- cluster:
    certificate-authority: /etc/kubernetes/admission/external-cert.pem  # CA for verifying the remote service.
    server: https://external-service:1234/check-image                   # URL of remote service to query. Must use 'https'.
  name: image-checker

contexts:
- context:
    cluster: image-checker
    user: api-server
  name: image-checker
current-context: image-checker
preferences: {}

# users refers to the API server's webhook configuration.
users:
- name: api-server
  user:
    client-certificate: /etc/kubernetes/admission/apiserver-client-cert.pem     # cert for the webhook admission controller to use
    client-key:  /etc/kubernetes/admission/apiserver-client-key.pem             # key matching the cert

External service deployment

root@controlplane:~# cat image-policy-webhook.yaml 
apiVersion: v1
kind: Service
metadata:
  labels:
    app: image-bouncer-webhook
  name: image-bouncer-webhook
spec:
  type: NodePort
  ports:
    - name: https
      port: 443
      targetPort: 1323
      protocol: "TCP"
      nodePort: 30080
  selector:
    app: image-bouncer-webhook
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: image-bouncer-webhook
spec:
  selector:
    matchLabels:
      app: image-bouncer-webhook
  template:
    metadata:
      labels:
        app: image-bouncer-webhook
    spec:
      containers:
        - name: image-bouncer-webhook
          imagePullPolicy: Always
          image: "kainlite/kube-image-bouncer:latest"
          args:
            - "--cert=/etc/admission-controller/tls/tls.crt"
            - "--key=/etc/admission-controller/tls/tls.key"
            - "--debug"
            - "--registry-whitelist=docker.io,k8s.gcr.io"
          volumeMounts:
            - name: tls
              mountPath: /etc/admission-controller/tls
      volumes:
        - name: tls
          secret:
            secretName: tls-image-bouncer-webhook

Test ImagePolicyWebhook

root@cks-master:/etc/kubernetes/admission# k run test1 --image=nginxError from server (Forbidden): pods "test1" is forbidden: Post "https://external-service:1234/check-image?timeout=30s": dial tcp: lookup external-service on 169.254.169.254:53: no such host

Task

Convert the existing Deployment crazy-deployment to use the image digest of the current tag instead of the tag.

k get pod crazy-deployment-77869b449b-286sv -o jsonpath='{.status.containerStatuses[*].imageID}'

k set image deployment crazy-deployment *=docker.io/library/httpd@sha256:c7b8040505e2e63eafc82d37148b687ff488bf6d25fc24c8bf01d71f5b457531