Integrate Kubernetes cert-manager with an internal ACME CA

About this tutorial

In this example, we'll configure Kubernetes cert-manager to get a certificate from an internal ACME server, using cert-manager's ACME issuer.

  • Estimated effort: Reading time ~4 mins, Lab time ~20 to 60 mins.


0. Before you begin

This example uses the ACME dns-01 challenge type, with Google Cloud DNS. We'll create a service account on Google Cloud that cert-manager will use to solve DNS challenges. For other DNS providers, or other ACME challenge types, you'll need to change the challenge solver settings below.

1. Create a Kubernetes cluster

For this tutorial, I created a Google Compute Engine VM running a kind cluster. I'm using kind for testing, but pretty much any Kubernetes cluster will do.

$ kind cluster create

2. Set up cert-manager to trust your internal CA

Let's install Kubernetes cert-manager and patch it so that it will trust your internal ACME CA.

First, install cert-manager:

$ kubectl apply --validate=false -f

Next, create a ConfigMap that contains your ACME server's CA certificate. To find your certificate's PEM file, select your CA in the Google Cloud CAS Console, and view your CA certificate under the Actions menu.

Create a file called internal-ca.yaml, replacing the certificate shown here with your own:

apiVersion: v1 data: internal-ca.pem: | -----BEGIN CERTIFICATE----- [REPLACE with your CA certificate] -----END CERTIFICATE----- kind: ConfigMap metadata: name: ca-pemstore namespace: cert-manager resourceVersion: "9978" selfLink: /api/v1/namespaces/cert-manager/configmaps/ca-pemstore ---

Apply it:

$ kubectl apply -f internal-ca.yaml

To inject this ConfigMap into cert-manager, we need to patch the cert-manager Deployment to add the CA certificate as a container volume mount.

Create a file called cm-ca-patch.yaml:

spec: template: spec: containers: - args: - --v=2 - --cluster-resource-namespace=$(POD_NAMESPACE) - --leader-election-namespace=kube-system name: cert-manager volumeMounts: - name: ca-pemstore mountPath: /etc/ssl/certs/internal-ca.pem subPath: internal-ca.pem readOnly: false resources: {} volumes: - name: ca-pemstore configMap: # Provide the name of the ConfigMap containing the files you want # to add to the container name: ca-pemstore

Apply the patch:

$ kubectl patch deployment cert-manager -n cert-manager --patch "$(cat cm-ca-patch.yaml)"

Cert-manager is now configured to trust your ACME CA.

3. Create a GCP service account and import its credentials

Not using Google Cloud Platform? You can skip this step and configure the cert-manager Issuer in step 4 to use a different challenge solver. See cert-manager's documentation for http-01 and dns-01 solvers.

We're going to have cert-manager solve dns-01 ACME challenges. So, it will need to be able to manage DNS entries.

Let's create a Google Cloud Platform service account with the roles/dns.admin role. Replace the PROJECT_ID here with your own:

$ export PROJECT_ID=step-cas-test $ gcloud iam service-accounts create dns01-solver \ --project $PROJECT_ID --display-name "dns01-solver" $ gcloud projects add-iam-policy-binding $PROJECT_ID \ --member serviceAccount:dns01-solver@$ \ --role roles/dns.admin

Now import the service account's credentials as a Kubernetes secret:

$ gcloud iam service-accounts keys create key.json \ --iam-account dns01-solver@$ $ kubectl create secret generic clouddns-dns01-solver-svc-acct \ --from-file=key.json

4. Create the cert-manager Issuer

Finally, let's create an cert-manager Issuer to perform dns-01 ACME challenges. Make a new file called acme-issuer.yaml:

apiVersion: kind: Issuer metadata: name: acme-issuer spec: acme: email: server: https://ca.smallstep.internal/acme/acme/directory privateKeySecretRef: name: acme-issuer-account-key solvers: - dns01: cloudDNS: # Your Google Cloud Platform project ID: project: step-cas-test # Your Google CloudDNS zone name we will use for DNS01 challenges: hostedZoneName: step-cas-internal serviceAccountSecretRef: name: clouddns-dns01-solver-svc-acct key: key.json

Replace the values for email, server URL, project and hostedZoneName with your own. Your Smallstep ACME endpoint will always take the form of https://[your CA hostname]/acme/acme/directory.

Apply it:

$ kubectl apply -f acme-issuer.yaml

You now have an automated ACME certificate manager running inside your Kubernetes cluster.

5. Issue a test certificate

Let's get a test certificate from our ACME CA, using a Certificate object. Create a file called tls-certificate.yaml:

apiVersion: kind: Certificate metadata: name: k8s-internal namespace: default spec: secretName: k8s-internal-tls issuerRef: name: acme-issuer dnsNames: - k8s.smallstep.internal

Replace the dnsNames value with a DNS name that's inside your zone.

Apply it:

$ kubectl apply -f tls-certificate.yaml

You can check the status with kubectl get certificaterequest or kubectl describe certificate:

$ kubectl get certificaterequest NAME READY AGE k8s-internal-nzbnm True 7s $ kubectl describe certificate k8s-internal Name: k8s-internal Namespace: default ... Kind: Certificate Metadata: Creation Timestamp: 2020-11-03T23:06:46Z ... Spec: Dns Names: k8s.smallstep.internal Issuer Ref: Name: acme-issuer Secret Name: k8s-internal-tls Status: Conditions: Last Transition Time: 2020-11-03T23:11:01Z Message: Certificate is up to date and has not expired Reason: Ready Status: True Type: Ready Not After: 2020-11-04T23:11:01Z Not Before: 2020-11-03T23:11:01Z Renewal Time: 2020-11-04T15:11:01Z Revision: 1 Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Issuing 10m cert-manager Issuing certificate as Secret does not exist Normal Generated 10m cert-manager Stored new private key in temporary Secret resource "k8s-internal-g79jq" Normal Requested 10m cert-manager Created new CertificateRequest resource "k8s-internal-nzbnm" Normal Issuing 9m33s cert-manager The certificate has been successfully issued

As you can see, cert-manager will automatically renew the certificate when approximately 2/3 of its lifetime has elapsed.

That's it! You now have automated, short-lived certificates for your Kubernetes cluster. There are many use cases for X.509 certificates issued through cert-manager.