Google Certificate Authority Service Issuer for cert-manager

This repository contains an external Issuer for cert-manager that issues certificates using Google Cloud Certificate Authority Service (CAS), using managed private CAs to issue certificates.

Getting started

Prerequisites

CAS-enabled GCP project

Enable the Certificate Authority API (privateca.googleapis.com) in your GCP project by following the official documentation.

CAS-managed Certificate Authorities

You can create a ca pool containing a certificate authority in your current Google project with:

gcloud privateca pools create my-pool --location us-east1
gcloud privateca roots create my-ca --pool my-pool --key-algorithm "ec-p384-sha384" --subject="CN=my-root,O=my-ca,OU=my-ou" --max-chain-length=2 --location us-east1

You should also enable the root CA you just created when prompted by gcloud.

It is recommended to create subordinate CAs for signing leaf certificates. See the official documentation.

cert-manager

If not already running in the cluster, install cert-manager by following the official documentation.

Installing Google CAS Issuer for cert-manager

helm repo add jetstack https://charts.jetstack.io --force-update
helm upgrade -i cert-manager-google-cas-issuer jetstack/cert-manager-google-cas-issuer -n cert-manager --wait

Or alternatively, assuming that you have installed cert-manager in the cert-manager namespace, you can use a single kubectl command to install Google CAS Issuer. Visit the GitHub releases, select the latest release and copy the command, e.g.

kubectl apply -f https://github.com/jetstack/google-cas-issuer/releases/download/v0.6.1/google-cas-issuer-v0.6.1.yaml

You can then skip to the Setting up Google Cloud IAM section.

Build and push the controller image

Note: you can skip this step if using the public images at quay.io.

Build the docker image:

make docker-build

Push the docker image or load it into kind for testing

make docker-push || kind load docker-image quay.io/jetstack/cert-manager-google-cas-issuer:latest

Deploy the controller

Deploy the issuer controller:

cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: google-cas-issuer
  namespace: cert-manager
  labels:
    app: google-cas-issuer
spec:
  selector:
    matchLabels:
      app: google-cas-issuer
  replicas: 1
  template:
    metadata:
      labels:
        app: google-cas-issuer
    spec:
      serviceAccountName: ksa-google-cas-issuer
      containers:
      # update the image to your registry if you built and pushed your own image.
      - image: quay.io/jetstack/cert-manager-google-cas-issuer:latest
        imagePullPolicy: IfNotPresent
        name: google-cas-issuer
        resources:
          limits:
            cpu: 100m
            memory: 30Mi
          requests:
            cpu: 100m
            memory: 20Mi
      terminationGracePeriodSeconds: 10
EOF

By default, the Google CAS Issuer controller will be deployed into the cert-manager namespace.

NAME                                      READY   STATUS    RESTARTS   AGE
cert-manager-6cd8cb4b7c-m8q4k             1/1     Running   0          34h
cert-manager-cainjector-685b87b86-4jvtb   1/1     Running   1          34h
cert-manager-webhook-76978fbd4c-rrx85     1/1     Running   0          34h
google-cas-issuer-687685dc46-lrjkc        1/1     Running   0          28h

Setting up Google Cloud IAM

Firstly, create a Google Cloud IAM service account. This service account will be used by the CAS Issuer to access the Google Cloud CAS APIs.

gcloud iam service-accounts create sa-google-cas-issuer

Apply the appropriate IAM bindings to this account. This example permits the least privilege, to create certificates (ie roles/privateca.certificates.create) from a specified CA pool (my-pool), but you can use other roles as necessary (see Predefined Roles for more details).

gcloud privateca pools add-iam-policy-binding my-pool --role=roles/privateca.certificateRequester --member="serviceAccount:sa-google-cas-issuer@$(gcloud config get-value project | tr ':' '/').iam.gserviceaccount.com" --location=us-east1

Inside GKE with workload identity

Workload identity lets you bind a Kubernetes service account to a Google Cloud service account. In order to take advantage of this, your GKE cluster must be set up to use it. If you want to create a cluster from scratch to test the issuer, you can enable it like so:

gcloud container clusters create test --region us-east1 --num-nodes=1 --preemptible \
  --workload-pool=$(gcloud config get-value project | tr ':' '/').svc.id.goog

If you want to use the CAS issuer in an existing cluster, you can still enable the workload identity feature with:

gcloud container clusters update CLUSTER_NAME --region=CLUSTER_REGION \
  --workload-pool="$(gcloud config get-value project | tr ':' '/').svc.id.goog"

Bind the Kubernetes service account (ksa-google-cas-issuer) to the Google Cloud service account:

export PROJECT=$(gcloud config get-value project | tr ':' '/')

gcloud iam service-accounts add-iam-policy-binding \
  --role roles/iam.workloadIdentityUser \
  --member "serviceAccount:$PROJECT.svc.id.goog[cert-manager/ksa-google-cas-issuer]" \
  sa-google-cas-issuer@${PROJECT:?PROJECT is not set}.iam.gserviceaccount.com

kubectl annotate serviceaccount \
  --namespace cert-manager \
  ksa-google-cas-issuer \
  iam.gke.io/gcp-service-account=sa-google-cas-issuer@${PROJECT:?PROJECT is not set}.iam.gserviceaccount.com \
  --overwrite=true

Outside GKE or in an unrelated GCP project

Create a key for the service account and download it to a local JSON file.

gcloud iam service-accounts keys create $(gcloud config get-value project | tr ':' '/')-key.json \
  --iam-account sa-google-cas-issuer@$(gcloud config get-value project | tr ':' '/').iam.gserviceaccount.com

The service account key should be stored in a Kubernetes secret in your cluster so it can be accessed by the CAS Issuer controller.

 kubectl -n cert-manager create secret generic googlesa --from-file $(gcloud config get-value project | tr ':' '/')-key.json

Configuring the Issuer

cert-manager is configured for Google CAS using either a GoogleCASIssuer (namespace-scoped) or a GoogleCASClusterIssuer (cluster-wide).

Inspect the sample configurations below and update the PROJECT_ID as appropriate. Credentials can be omitted if you have configured the CAS issuer controller with Workload Identity.

# googlecasissuer-sample.yaml
apiVersion: cas-issuer.jetstack.io/v1beta1
kind: GoogleCASIssuer
metadata:
  name: googlecasissuer-sample
spec:
  project: $PROJECT_ID
  location: us-east1
  caPoolId: my-pool
  # credentials are optional if workload identity is enabled
  credentials:
    name: "googlesa"
    key: "$PROJECT_ID-key.json"

kubectl apply -f googlecasissuer-sample.yaml

or

# googlecasclusterissuer-sample.yaml
apiVersion: cas-issuer.jetstack.io/v1beta1
kind: GoogleCASClusterIssuer
metadata:
  name: googlecasclusterissuer-sample
spec:
  project: $PROJECT_ID
  location: us-east1
  caPoolId: my-pool
  # credentials are optional if workload identity is enabled
  credentials:
    name: "googlesa"
    key: "$PROJECT_ID-key.json"

kubectl apply -f googlecasclusterissuer-sample.yaml

Creating your first certificate

You can now create certificates as normal, but ensure the IssuerRef is set to the GoogleCASIssuer or GoogleCASClusterIssuer created in the previous step.

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: demo-certificate
  namespace: default
spec:
  # The secret name to store the signed certificate
  secretName: demo-cert-tls
  # Common Name
  commonName: cert-manager.io.demo
  # DNS SAN
  dnsNames:
    - cert-manager.io
    - jetstack.io
  # Duration of the certificate
  duration: 24h
  # Renew 8 hours before the certificate expiration
  renewBefore: 8h
  # Important: Ensure the issuerRef is set to the issuer or cluster issuer configured earlier
  issuerRef:
    group: cas-issuer.jetstack.io
    kind: GoogleCASClusterIssuer # or GoogleCASIssuer
    name: googlecasclusterissuer-sample # or googlecasissuer-sample

kubectl apply -f demo-certificate.yaml

In short time, the certificate will be requested and made available to the cluster.

kubectl get certificates,secret
NAME                                           READY   SECRET         AGE
certificate.cert-manager.io/demo-certificate   True    demo-cert-tls  1m

NAME                                     TYPE                                  DATA   AGE
secret/demo-cert-tls                     kubernetes.io/tls                     3      1m