Kubernetes Mutating Webhook for Secret replication

The responsibility of this webhook is to patch all newly created/updated namespaces so that they contain predefined empty secret with given annotation.

This repo produces one helm chart available via helm repository https://ysoftdevs.github.io/secret-duplicator. There are also 2 docker images:

• ghcr.io/ysoftdevs/secret-duplicator/secret-duplicator - the image containing the webhook itself
• ghcr.io/ysoftdevs/secret-duplicator/webhook-cert-generator - helper image responsible for (re)generating the certificates

Helm description

The helm chart consists of 2 parts: the certificate generator and the webhook configuration itself.

Certificate generation part periodically generates certificates signed by kubernetes' CA and passes them to the webhook where they are used as server-side certificates. The flow works roughly like this:

1. We generate a CSR using openssl and tie the certificate to the webhook's service DNS.
2. We create a k8s CertificateSigningRequest from the openssl CSR.
3. We approve this request using our special ServiceAccount with approve permissions. This makes kubernetes issue the certificate
4. We fetch the certificate from the k8s CSR (at .status.certificate) and create a secret from it
5. We also create a CronJob that does this periodically as k8s only issues certificates for 1 year

The main part is the deployment and the web hook configuration. The flow is as follows

1. The MutatingWebhookConfiguration we create instructs k8s to pass all requests for creating/updating all Namespaces to our webhook before finishing the request
2. We check whether the Namespaces has the correctly defined secret configuration. if not, we create the secret.
3. We also check whether we have the secret with correct annotation. If not, we update the secret

Of note is also a fact that the chart runs a lookup to the connected cluster to fetch the CA bundle for the MutatingWebhook. This means helm template won't work.

Running locally

1. Create the prerequisite resources:

   kubectl create ns secret-duplicator
   
   kubectl create secret -n secret-duplicator \
       generic acr-dockerconfigjson-source \
       --type=kubernetes.io/dockerconfigjson \
       --from-literal=.dockerconfigjson='<your .dockerconfigjson configuration file>'

2. Build the images and run the chart

   make build-image
   helm upgrade -i secret-duplicator \
       -n secret-duplicator \
       charts/secret-duplicator

   Alternatively, you can use the pre-built, publicly available helm chart and docker images:

   helm repo add secret-duplicator https://ysoftdevs.github.io/secret-duplicator
   helm repo update
   helm upgrade -i secret-duplicator \
       -n secret-duplicator \
       secret-duplicator/secret-duplicator

3. To test whether everything works, you can run

   kubectl create ns yolo    

   The get command should display some non-empty result.

Releasing locally

To authenticate to the docker registry to push the images manually, you will need your own Github Personal Access Token. For more information follow this guide https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry#authenticating-to-the-container-registry