image-clone-controller

A Kubernetes controller which watches the applications and "caches" the images by re-uploading to our own registry repository and reconfiguring the applications to use these copies.

Demo

The controller in action: https://asciinema.org/a/O7Qk6BiZaoAiVMUSaXkOBkOdM

You can actually spot it doing its thing on itself directly after deploying. But after that the functionality is demonstrated on an example nginx deployment.

Prerequisites

Kubebuilder (Project was scaffolded with version 3.0.0-beta.0. Earlier version might not work.)
docker (>=19.0 - Earlier versions might work but were not tested.)

Setting up the Backup Registry

Either create a file ./config/manager/secrets/.dockerconfigjson with the content:

{
  "auths": {
    "<registry>": {
      "username": "<username>",
      "password": "<password>",
      "email": "<email>",
      "auth": "<base64 encoded '<username>:<password>'>"
    }
  }
}

or just run hack/generate_pull_secret.sh and follow the prompt.

How to deploy

$ export IMG="<registry>/<image>:<tag>"
$ make docker-build
$ make docker-push
$ make deploy

Known bugs

Some source images when retagged trigger a 401 Unauthorized when pushed to the "backup registry".
No testing.

Disclaimer

This is my first Kubernetes controller, so this probably is far from best practices. There are always things to improve, but learning to write a controller by doing it while working and having 2 kids at home during corona are the reasons why I kept the scope pretty narrow and went for the naive/pragmatic approach. (Like always copying the image, since the push will figure out if it already exists remotely.)

Nevertheless it was a great learning experience. kubebuilder took care of a lot of scaffolding and also helped leading the way.

I still have no clue how to properly test a controller. :(