Kubernetes Image Mapper Prototype

The goal of this repository is to allow a kubernetes application to be deployed with images which have been moved to a private registry, but without editing the application configuration. A webhook rewrites the image references in the application's pods according to a mapping which is configured using custom resources.

To do:

• Additional features - see issues

For more context, please see the image relocation repository's README.

Details

This repository consists of a MutatingAdmissionWebhook which rewrites kubernetes pods to use relocated image references. The mapping from original to relocated image references is built by deploying imagemap custom resources which are processed by a controller also provided by this repository.

Each imagemap is namespaced and applies only to pods in the same namespace.

When an imagemap is deployed, if it is inconsistent with other imagemaps in the namespace, it is rejected and the status of the imagemap details the inconsistency (in a Ready condition with status false). After the inconsistency has been corrected, the rejected imagemap is automatically redeployed after a short delay (currently one minute).

If an imagemap is updated and this results in the imagemap being rejected, the original imagemap is undeployed.

Usage

The following was tested using a GKE cluster.

• Install Jetstack certificate manager:

kubectl create namespace cert-manager && \
kubectl apply --validate=false -f https://github.com/jetstack/cert-manager/releases/download/v0.12.0/cert-manager.yaml

• If you want the controller and webhook to provide detailed logs, enable debug logging in the currently active patch file, such asconfig/default/manager_auth_proxy_patch.yaml, like this:

      ...
      - name: manager
        args:
        - "--metrics-addr=127.0.0.1:8080"
        - "--enable-leader-election"
        - "--debug"
      ...

• Build and deploy the webhook:

make docker-build docker-push IMG=<some-registry>/<project-name>:tag &&
make deploy IMG=<some-registry>/<project-name>:tag

• Deploy a sample imagemap custom resource, after editing it to replace <repo prefix> with a suitable repository prefix (e.g. gcr.io/my-sandbox) to which you and the cluster have access:

# remember to edit config/samples/mapper_v1alpha1_imagemap.yaml
kubectl apply -f config/samples/mapper_v1alpha1_imagemap.yaml

• Observe the image map resources:

kubectl get imagemaps

Output:

NAME              AGE
bootcamp-sample   1m

• Create a pod, e.g.:

kubectl run kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1 --port=8080

• Observe the relocated image in the pod, e.g.:

kubectl get pod kubernetes-bootcamp-xxx -oyaml

Output:

...
spec:
  containers:
  - image: <repo prefix>/kubernetes-bootcamp:v1
...

Note: the image value under containerStatuses may not be the relocated value. This is a known issue when an image has multiple references referring to it.

• View the logs from the webhook, e.g.:

kubectl logs image-mapper-controller-manager-xxx -n image-mapper-system

• Now tidy up:

kubectl delete deployment kubernetes-bootcamp
kubectl delete -f config/samples/mapper_v1alpha1_imagemap.yaml
make undeploy IMG=<some-registry>/<project-name>:tag
kubectl delete -f https://github.com/jetstack/cert-manager/releases/download/v0.12.0/cert-manager.yaml