A Kubernetes ClusterSecret

No, at this moment ClusterSecret, unlike ClusterRole, doesn’t officially exist in any version of Kubernetes yet. I’ve seen some discussion like this, so looks like it will be a while to have a ClusterSecret.

But why do I need a ClusterSecret in the first place? The reason is very simple: To be DRY. Imagine I have a few apps deployed into several different namespaces and they all need to pull from my private docker registry. This looks like:

├── namespace-1
│   ├── image-pull-secret
│   └── deployment-app-1
├── namespace-2
│   ├── image-pull-secret
│   └── deployment-app-2
...

It’s a tad straight forward that all the image-pull-secret secrets are the same but as there’s no ClusterSecret they have to be duplicated all over the place. And to make things nicer, if the private registry changes its token, all of these secrets need to be updated at once.

Of course I’m not the first one to be frustrated by this and there are tools built by the community already. ClusterSecret operator is one of them. But when I looked at kubernetes-reflector I immediately liked its simple approach: it can reflects 1 source secret or configmap to many mirror ones in all namespaces! Also it’s easy to integrate with existing SealedSecret operator with reflector.

Here’s how to install kubernetes-reflector quickly with all default settings(copied from its README). I chose to save this file and let my FluxCD to install it for me.

kubectl apply -f https://github.com/emberstack/kubernetes-reflector/releases/latest/download/reflector.yaml

Now I can create a image pull secret for my private docker registry in kube-system namespace and then the reflector will copy it to a few namespaces which match the regex for the namespace whitelist.

The command to create a image pull secret is

kubectl create secret docker-registry image-pull-secret -n kube-system --docker-server=<your-registry-server> --docker-username=<your-name> --docker-password=<your-pword> --docker-email=<your-email>

The full sealed secret command will be

kubectl create secret docker-registry image-pull-secret -n kube-system --docker-server=<your-registry-server> --docker-username=<your-name> --docker-password=<your-pword> --docker-email=<your-email> | \
  kubeseal --controller-namespace=sealed-secrets --controller-name=sealed-secrets -o yaml > image-pull-secret.yaml

Then I’ll add a few magic annotation to let the reflector pick up the job

# this is image-pull-secret.yaml
apiVersion: bitnami.com/v1alpha1
kind: SealedSecret
metadata:
  creationTimestamp: null
  name: image-pull-secret
  namespace: kube-system
spec:
  encryptedData:
    .dockerconfigjson: AgA4E6mcpri...
  template:
    metadata:
      creationTimestamp: null
      name: image-pull-secret
      namespace: kube-system
      annotations:
        reflector.v1.k8s.emberstack.com/reflection-allowed: "true"
        reflector.v1.k8s.emberstack.com/reflection-auto-enabled: "true"
        reflector.v1.k8s.emberstack.com/reflection-auto-namespaces: "wordpress-.*"
status: {}

So when I deploy this file, first the SealedSecret operator will decrypt this into a normal secret with those annotations(note. adding annotations won’t break the encryption, but changing name or namespace could). And then the reflector will create the image-pull-secret secrets in all namespaces which start with wordpress- prefix.

Mission accomplished 🙂

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