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Integrate Certificate Manager with Autocert for Kubernetes TLS

Autocert exists to make it easy to use mutual TLS to improve security within a cluster and to secure communication into, out of, and between Kubernetes clusters. To get a certificate you simply need to telll autocert your workload's name, using the autocert.step.sm/namepod annotation. Autocert will issue a cert to the pod, make it available in var/run/autocert.step.sm, and keep it renewed. It requires a certificate authority to issue certificates. This guide shows how to configure autocert to use Certificate Manager as the upstream CA.

Before you begin

You will need:

  • An account on the Smallstep platform. Need one? Register here
  • An Authority in Certificate Manager that will act as your upstream CA

Bootstrap with your CA

Bootstrapping with your Authority configures your workstation to trust the authority's root certificate.

Run:

step ca bootstrap --ca-url [your CA URL] \
    --fingerprint [your CA fingerprint] \
    --install

Add a provisioner

Autocert requires a JWK provisioner (it's the default type). Let's call it autocert. Run:

step ca provisioner add autocert --create

You’ll be asked to provide a password to encrypt the provisioner private key.

Create ConfigMaps and a Secret for Autocert

In Kubernetes, create a namespace for autocert:

kubectl create ns step

Output:

namespace/step created

Use the same password you entered when creating the provisioner to create the Secret.

kubectl -n step create secret generic autocert-password --from-file=password=autocert-password.txt

Output:

secret/autocert-password created

Now create a ConfigMap that includes your (bootstrapped) config dir:

kubectl -n step create configmap config --from-file $(step path)/config`

Output:

configmap/config created

We'll do the same thing for the certs dir, which contains our CA's root certificate:

kubectl -n step create configmap certs --from-file $(step path)/certs

Output:

configmap/certs created

Deploy Autocert

  1. Download the yaml config:

    curl -O https://raw.githubusercontent.com/smallstep/autocert/master/install/02-autocert.yaml

  2. Edit the caUrl in the autocert-config ConfigMap in the 02-autocert.yaml file you just downloaded. Change it from https://ca.step.svc.cluster.local to your Certificate Manager authority URL, e.g. https://autocert.areed.ca.smallstep.com.

  3. Run:

    kubectl apply -f https://raw.githubusercontent.com/smallstep/autocert/master/install/03-rbac.yaml

    Output:

    clusterrole.rbac.authorization.k8s.io/autocert-controller created
clusterrolebinding.rbac.authorization.k8s.io/autocert-controller created

  4. Now let's deploy autocert. Run:

    kubectl apply -f 02-autocert.yaml

    Output:

    service/autocert created
configmap/autocert-config created
deployment.apps/autocert created

  5. And, let's deploy the admission webhook:

    You can see in this block that we're including the root CA certificate (in base64) as part of the client configuration for autocert.

    cat <<EOF | kubectl apply -f -
apiVersion: admissionregistration.k8s.io/v1
kind: MutatingWebhookConfiguration
metadata:
  name: autocert-webhook-config
  labels: {app: autocert}
webhooks:
  - name: autocert.step.sm
    sideEffects: None
    admissionReviewVersions: ["v1beta1"]
    clientConfig:
      service:
        name: autocert
        namespace: step
        path: "/mutate"
      caBundle: $(cat $(step path)/certs/root_ca.crt | base64 | tr -d '\n')
    rules:
      - operations: ["CREATE"]
        apiGroups: [""]
        apiVersions: ["v1"]
        resources: ["pods"]
    namespaceSelector:
      matchLabels:
        autocert.step.sm: enabled
EOF

    output:

    mutatingwebhookconfiguration.admissionregistration.k8s.io/autocert-webhook-config created

Autocert is now added to the cluster and configured. You can run this command to verify the autocert pods are marked Ready.

kubectl -n step get deployment/autocert

Usage

Let’s create a test app that will use autocert. It’s a “Hello World” web server that uses mutual TLS authentication.

Since this deployment is in the default namespace, label it to tell autocert to issue and renew certificates for new pods with the autocert.step.sm/name annotation:

kubectl label namespace default autocert.step.sm=enabled

Output:

namespace/default labeled

To test things out, we'll create a deployment with the autocert.step.sm/name pod annotation. This example uses the name localhost, since we will be testing from our workstation.

cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: hello-mtls
  name: hello-mtls
spec:
  selector:
    matchLabels:
      app: hello-mtls
  template:
    metadata:
      annotations:
        autocert.step.sm/name: localhost
      labels:
        app: hello-mtls
    spec:
      containers:
      - image: smallstep/hello-mtls-server-go:latest
        name: hello-mtls
EOF

Output:

deployment.apps/hello-mtls created

For testing, forward localhost:8443 to port 443 on the pod.

kubectl port-forward deploy/hello-mtls 8443:443

Output:

Forwarding from 127.0.0.1:8443 -> 443
Forwarding from [::1]:8443 -> 443

Keep this running in the background during the next steps.

Now issue a client certificate signed by your CA. You’ll need this to authenticate to the “Hello mTLS” test server.

step ca certificate andrew@smallstep.com areed.crt areed.key

Finally, you should be able to verify it's all working:

curl --cacert $(step path)/certs/root_ca.crt \
     --cert areed.crt --key areed.key \
     https://localhost:8443

Output:

Hello andrew@smallstep.com!
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