k8s-duplicator

k8s-duplicator

k8s-duplicator is a kubernetes controller that duplicates secrets from one to all other namespaces and keeps them in sync.

Motivation

This controller can be used to sync any secret into all namespaces by adding the annotation duplicator.k8s.nicktriller.com/duplicate: "true" to the secret.

My specific use case for this controller is provisioning a wildcard certificate with cert-manager and then making the certificate available in all namespaces as described in the cert manager docs:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: wildcard-k8s-nicktriller-com
  namespace: kube-system
spec:
  dnsNames:
  - '*.k8s.nicktriller.com'
  issuerRef:
    group: cert-manager.io
    kind: ClusterIssuer
    name: letsencrypt-prod
  secretName: wildcard-k8s-nicktriller-com
  secretTemplate:
    annotations:
      # Annotation that instructs k8s-duplicator to duplicate the certificate secret to all namespaces
      duplicator.k8s.nicktriller.com/duplicate: "true"

kubernetes-reflector is a similar project with more features that can be used to achieve the same goal, but it had reliability problems - it would randomly stop reconciling secrets until it was restarted. Also, implementing my own controller seemed like a fun project.

Install

See chart README for available config options.

helm repo add k8s-duplicator https://nicktriller.github.io/k8s-duplicator/
helm repo update
helm upgrade --install -n k8s-duplicator --create-namespace k8s-duplicator k8s-duplicator/k8s-duplicator

Usage

Add the annotation duplicator.k8s.nicktriller.com/duplicate: "true" to a secret to duplicate it to all namespaces. The copies will be kept in sync with the original secret. Copies are deleted if the original secret is deleted or the duplicate annotation is removed from the original secret. Copies have the same name as the original secret. If a namespace already contains a secret with the same name as the original secret, the controller will not overwrite it. Labels and annotations are not copied from the original secret to the copies.

apiVersion: v1
kind: Secret
metadata:
  name: my-secret
  namespace: some-namespace
  annotations:
    duplicator.k8s.nicktriller.com/duplicate: "true"
stringData:
  foo: bar

The copies are annotated with an annotation that references the original secret:

apiVersion: v1
kind: Secret
metadata:
  name: my-secret
  namespace: another-namespace
  annotations:
    duplicator.k8s.nicktriller.com/source: "some-namespace/my-secret"
stringData:
  foo: bar

Release process

Push a git tag in the form of docker-1.0.0 on main branch to publish a docker image to dockerhub. The docker image will be tagged with the version given in the git tag.

Push a git tag in the form of helm-1.0.0 on main branch to publish the helm chart. The chart is packaged and pushed into gh_pages branch with the chart version set to the version given in the git tag. appVersion in Chart.yaml is not overwritten by CI.

Make sure to update the the helm chart changelog and application changelog as appropriate.