Yrden zeichen is a prototype of kubernetes admission controller. The idea is to create highly-customizable and configurable admission webhook for kubernetes which will keep bad deployments out of cluster.

TODO: describe deployment without embedding certificates into the pod

1. Create namespace for yrdenzeichen

   $ kubectl create namespace yrdenzeichen
   namespace/yrdenzeichen created

2. Generate ssl certificate and key for yrdenzeichen. For example, the Manage TLS Certificates in a Cluster guide can be followed.

3. As soon as you have both key (server.key.pem) and certificate (server.crt.pem) generate a Kubernetes secret with those:

   $ kubectl -n yrdenzeichen create secret generic yrdenzeichen-certs \
       --from-file server.crt.pem \
       --from-file server.key.pem
   secret/yrdenzeichen-certs created

4. Create deployment manifest for yrdenzeichen

   ---
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: yrdenzeichen
     namespace: yrdenzeichen
     labels:
       app.kubernetes.io/name: admission-webhook
       app.kubernetes.io/instance: yrdenzeichen
   spec:
     replicas: 3
     selector:
       matchLabels:
         app.kubernetes.io/name: admission-webhook
         app.kubernetes.io/instance: yrdenzeichen
     template:
       metadata:
         labels:
           app.kubernetes.io/name: admission-webhook
           app.kubernetes.io/instance: yrdenzeichen
       spec:
         containers:
         - name: yrdenzeichen
           image: anxolerd/yrden:20200723.1219
           imagePullPolicy: IfNotPresent
           ports:
           - containerPort: 3000
             name: http
           - containerPort: 3001
             name: https
           env:
           - name: HTTP_PORT
             value: '3000'
           - name: HTTPS_PORT
             value: '3001'
           - name: METRICS_PORT
             value: '9090'
           volumeMounts:
           - name: yrdenzeichen-certs
             mountPath: '/etc/ssl/'
             readOnly: true
           resources:
             requests:
               cpu: 100m
               memory: 32Mi
             limits:
               cpu: 200m
               memory: 64Mi
         volumes:
         - name: yrdenzeichen-certs
           secret:
             secretName: yrdenzeichen-certs
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: webhook
     namespace: yrdenzeichen
   spec:
     ports:
       - name: https
         port: 443
         targetPort: https
       - name: http
         port: 80
         targetPort: http
     selector:
       app.kubernetes.io/name: admission-webhook
       app.kubernetes.io/instance: yrdenzeichen

5. Apply yrdenzeichen deployment manifest created in previous step

   $ kubectl apply -f deployment.yaml
   deployment/yrdenzeichen created
   service/webhook created

6. Create admission webhook registration manifest

   ---
   apiVersion: admissionregistration.k8s.io/v1beta1
   kind: ValidatingWebhookConfiguration
   metadata:
     name: yrdenzeichen
   webhooks:
   - name: webhook.yrdenzeichen.svc.cluster.local
     clientConfig:
       caBundle: <certificate authority root certificate in base64>
       service:
         name: webhook
         namespace: yrdenzeichen
         port: 443
     # Enable only on selected namespaces
     namespaceSelector:
       matchExpressions:
       - key: io.github.anxolerd.yrdenzeichen/validation
         operator: In
         values: ["enabled"]
     rules:
     - operations: ["CREATE", "UPDATE"]
       apiGroups: ["apps"]
       apiVersions: ["v1"]
       resources: ["deployments", "replicasets", "statefulsets"]
       scope: "Namespaced"
     - operations: ["CREATE", "UPDATE"]
       apiGroups: [""]
       apiVersions: ["v1"]
       resources: ["pods"]
       scope: "Namespaced"
     failurePolicy: Fail # Other possible value is `Ignore`

7. Apply admission webhook registration created in previous step

   $ kubectl apply -f webhook.yaml
   validatingwebhookconfiguration.admissionregistration.k8s.io/yrdenzeichen created

8. Label namespaces you want to validate

   $ kubectl label namespace your-namespace io.github.anxolerd.yrdenzeichen/validation=enabled

Enabled validators and groups are configured via app/config.js file.

Validators should follow the following API:

validator :: KubernetesObject -> {valid: bool, errors: string[]}

Yrden is a simple magical sign used by witchers. When inscribed on a solid surface, it blocks the monsters from getting closer, scaring them off. [...] In "The Witcher", a short story in The Last Wish, Geralt uses Yrden to ensure his own safety inside the sarcophagus.

—https://witcher.fandom.com/wiki/Yrden