geek-cookbook/docs/kubernetes/ssl-certificates/secret-replicator.md

Secret Replicator

As explained when creating our LetsEncrypt Wildcard certificates, it can be problematic that Certificates can't be shared between namespaces. One simple solution to this problem is simply to "replicate" secrets from one "source" namespace into all other namespaces.

!!! summary "Ingredients"

* [x] A [Kubernetes cluster](/kubernetes/cluster/) 
* [x] [Flux deployment process](/kubernetes/deployment/flux/) bootstrapped
* [x] [secret-replicator](/kubernetes/ssl-certificates/secret-replicator/) deployed to request/renew certificates
* [x] [LetsEncrypt Wildcard Certificates](/kubernetes/ssl-certificates/wildcard-certificate/) created in the `letsencrypt-wildcard-cert` namespace

Kiwigrid's "Secret Replicator" is a simple controller which replicates secrets from one namespace to another.¹

Preparation

Namespace

We need a namespace to deploy our HelmRelease and associated ConfigMaps into. Per the flux design, I create this example yaml in my flux repo:

apiVersion: v1
kind: Namespace
metadata:
  name: secret-replicator

HelmRepository

Next, we need to define a HelmRepository (a repository of helm charts), to which we'll refer when we create the HelmRelease. We only need to do this once per-repository. Per the flux design, I create this example yaml in my flux repo:

apiVersion: source.toolkit.fluxcd.io/v1beta1
kind: HelmRepository
metadata:
  name: kiwigrid
  namespace: flux-system
spec:
  interval: 15m
  url: https://kiwigrid.github.io

Kustomization

Now that the "global" elements of this deployment have been defined, we do some "flux-ception", and go one layer deeper, adding another Kustomization, telling flux to deploy any YAMLs found in the repo at /secret-replicator. I create this example Kustomization in my flux repo:

apiVersion: kustomize.toolkit.fluxcd.io/v1beta1
kind: Kustomization
metadata:
  name: secret-replicator
  namespace: flux-system
spec:
  interval: 15m
  path: ./secret-replicator
  prune: true # remove any elements later removed from the above path
  timeout: 2m # if not set, this defaults to interval duration, which is 1h
  sourceRef:
    kind: GitRepository
    name: flux-system
  validation: server
  healthChecks:
    - apiVersion: apps/v1
      kind: Deployment
      name: secret-replicator
      namespace: secret-replicator

ConfigMap

Now we're into the secret-replicator-specific YAMLs. First, we create a ConfigMap, containing the entire contents of the helm chart's values.yaml. Paste the values into a values.yaml key as illustrated below, indented 4 spaces (since they're "encapsulated" within the ConfigMap YAML). I create this example yaml in my flux repo:

apiVersion: v1
kind: ConfigMap
metadata:
  name: secret-replicator-helm-chart-value-overrides
  namespace: secret-replicator
data:
  values.yaml: |-
    # Default values for secret-replicator.
    # This is a YAML-formatted file.
    # Declare variables to be passed into your templates.

    image:
      repository: kiwigrid/secret-replicator
      tag: latest #0.2.0 It's 0.1.0 and latest listed in dockerhub. No 0.2.0 anymore 
      pullPolicy: IfNotPresent 
      ## Specify ImagePullSecrets for Pods
      ## ref: https://kubernetes.io/docs/concepts/containers/images/#specifying-imagepullsecrets-on-a-pod
      # pullSecrets: myregistrykey

    # csv list of secrets
    secretList: "letsencrypt-wildcard-cert"
    # secretList: "secret1,secret2

    ignoreNamespaces: "kube-system,kube-public"

    # If defined, allow secret-replicator to watch for secrets in _another_ namespace
    secretNamespace: "letsencrypt-wildcard-cert"

    rbac:
    enabled: true

    resources: {}
    # limits:
    #   cpu: 50m
    #   memory: 20Mi
    # requests:
    #   cpu: 20m
    #   memory: 20Mi

    nodeSelector: {}

    tolerations: []

    affinity: {}

--8<-- "kubernetes-why-full-values-in-configmap.md"

Note that the following values changed from default, above:

• secretList: letsencrypt-wildcard-cert
• secretNamespace: letsencrypt-wildcard-cert

HelmRelease

Lastly, having set the scene above, we define the HelmRelease which will actually deploy the secret-replicator controller into the cluster, with the config we defined above. I save this in my flux repo:

apiVersion: helm.toolkit.fluxcd.io/v2beta1
kind: HelmRelease
metadata:
  name: secret-replicator
  namespace: secret-replicator
spec:
  chart:
    spec:
      chart: secret-replicator
      version: 0.6.x
      sourceRef:
        kind: HelmRepository
        name: kiwigrid
        namespace: flux-system
  interval: 15m
  timeout: 5m
  releaseName: secret-replicator
  valuesFrom:
  - kind: ConfigMap
    name: secret-replicator-helm-chart-value-overrides
    valuesKey: values.yaml # This is the default, but best to be explicit for clarity

--8<-- "kubernetes-why-not-config-in-helmrelease.md"

Serving

Once you've committed your YAML files into your repo, you should soon see some pods appear in the secret-replicator namespace!

How do we know it worked?

Look for secrets across the whole cluster, by running kubectl get secrets -A | grep letsencrypt-wildcard-cert. What you should see is an identical secret in every namespace. Note that the Certificate only exists in the letsencrypt-wildcard-cert namespace, but the secret it generates is what gets replicated to every other namespace.

Troubleshooting

If your certificate is not created aren't created as you expect, then the best approach is to check the secret-replicator logs, by running kubectl logs -n secret-replicator -l app.kubernetes.io/name=secret-replicator.

--8<-- "recipe-footer.md"

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1. To my great New Zealandy confusion, "Kiwigrid GmbH" is a German company 🤷 ↩︎