Deploy Cerbos as a sidecar

The sidecar deployment model might be a preferrable option under the following circumstances:

You have a self-contained application that does not need to share policies with other applications in your environment.
You prefer to ship policy changes as application updates by bundling the two together.
You are concerned about network latency.

Cerbos supports serving the API over a Unix domain socket. This allows your application container to securely communicate with the Cerbos service with no network overhead. Because the Cerbos server is only listening over a Unix domain socket, no other applications in your network will be able to communicate with it — thus providing secrecy as a bonus side effect.

The following example illustrates a Kubernetes deployment with Cerbos as a sidecar.

We are using ghostunnel as the application container for demonstration purposes only. In a real production deployment the Cerbos endpoint should not be exposed to the network.

---
# Config map used to configure Cerbos.
apiVersion: v1
kind: ConfigMap
metadata:
  name: cerbos-sidecar-demo
  labels:
    app.kubernetes.io/name: cerbos-sidecar-demo
    app.kubernetes.io/component: cerbos
    app.kubernetes.io/version: "0.0.1"
data:
  ".cerbos.yaml": |-
      server:
        # Configure Cerbos to listen on a Unix domain socket.
        httpListenAddr: "unix:/sock/cerbos.sock"
      storage:
        driver: disk
        disk:
          directory: /policies
          watchForChanges: false
---
# Application deployment with Cerbos as a sidecar.
# Note that in this example we are simply proxying requests received
# by the main application (application container) to the Cerbos
# sidecar (`cerbos` container) for demonstration purposes. In a real
# production deployment the main application would not expose Cerbos
# to the outside world at all. It would communicate with the Cerbos
# sidecar privately to make policy decisions about the actions that
# it is performing.
#
# Bonus: You can re-purpose this example to deploy Cerbos in an
# environment that requires SPIFFE workload identities and/or
# regular certificate rotation and access restrictions. See the
# ghostunnel documentation at https://github.com/ghostunnel/ghostunnel
# for more information.
apiVersion: apps/v1
kind: Deployment
metadata:
  name: cerbos-sidecar-demo
  labels:
    app.kubernetes.io/name: cerbos-sidecar-demo
    app.kubernetes.io/component: cerbos-sidecar-demo
    app.kubernetes.io/version: "0.0.1"
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: cerbos-sidecar-demo
      app.kubernetes.io/component: cerbos-sidecar-demo
  template:
    metadata:
      labels:
        app.kubernetes.io/name: cerbos-sidecar-demo
        app.kubernetes.io/component: cerbos-sidecar-demo
    spec:
      containers:
        ########################################################################
        # Application container. Replace with your own application definition. #
        ########################################################################
        - name: application
          image: "ghostunnel/ghostunnel"
          imagePullPolicy: IfNotPresent
          args:
            - "server"
            - "--listen=:3592"
            - "--target=unix:/sock/cerbos.sock"
            - "--cert=/certs/tls.crt"
            - "--key=/certs/tls.key"
            - "--disable-authentication"
          ports:
            - name: http
              containerPort: 3592
          livenessProbe:
            httpGet:
              path: /_cerbos/health
              port: http
              scheme: HTTPS
          readinessProbe:
            httpGet:
              path: /_cerbos/health
              port: http
              scheme: HTTPS
          volumeMounts:
            # Mount the shared volume containing the socket
            - name: sock
              mountPath: /sock
            - name: certs
              mountPath: /certs
        ##################
        # Cerbos sidecar #
        ##################
        - name: cerbos
          image: "ghcr.io/cerbos/cerbos:0.39.0"
          imagePullPolicy: IfNotPresent
          args:
            - "server"
            - "--config=/config/.cerbos.yaml"
            - "--log-level=INFO"
          volumeMounts:
            # Mount the shared volume containing the socket
            - name: sock
              mountPath: /sock
            - name: config
              mountPath: /config
              readOnly: true
            - name: policies
              mountPath: /policies
      volumes:
        # Shared volume containing the socket.
        - name: sock
          emptyDir: {}
        - name: config
          configMap:
            name: cerbos-sidecar-demo
        - name: certs
          secret:
            secretName: cerbos-sidecar-demo
        - name: policies
          emptyDir: {}
---
# Use cert-manager to issue a certificate to the application.
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: cerbos-sidecar-demo
  labels:
    app.kubernetes.io/name: cerbos-sidecar-demo
    app.kubernetes.io/component: cerbos-sidecar-demo
    app.kubernetes.io/version: "0.0.1"
spec:
  isCA: true
  secretName: cerbos-sidecar-demo
  dnsNames:
    - cerbos-sidecar-demo.default.svc.cluster.local
    - cerbos-sidecar-demo.default.svc
    - cerbos-sidecar-demo.default
    - cerbos-sidecar-demo
  issuerRef:
    name: selfsigned-cluster-issuer
    kind: ClusterIssuer
    group: cert-manager.io