Using cert-manager

Ambassador Edge Stack has simple and easy built-in support for automatically using ACME with the http-01 challenge to create and renew TLS certificates. However, this support is not available in Emissary, and it is limited to the ACME http-01 challenge type. If you’re running Emissary, or if you require more flexible certificate management (such as using ACME’s dns-01 challenge, or using a non-ACME certificate source), external certificate management tools are also supported.

One such tool is Jetstack’s cert-manager, which is a general-purpose tool for managing certificates in Kubernetes. Cert-manager will automatically create and renew TLS certificates and store them as Kubernetes secrets for easy use in a cluster. Emissary will automatically watch for secret changes and reload certificates upon renewal.

Note: This document assumes cert-manager v0.15 or greater. This document has been updated to use CRD standards specified in v0.15. Legacy CRD support was removed in cert-manager v0.15, see their upgrading document for more info.

Install cert-manager

There are many different ways to install cert-manager. For simplicity, we will use Helm.

Create the cert-manager CRDs.

kubectl apply -f https://github.com/jetstack/cert-manager/releases/latest/download/cert-manager.crds.yaml

Add the jetstack Helm repository.

helm repo add jetstack https://charts.jetstack.io && helm repo update

Install cert-manager.

kubectl create ns cert-manager
helm install cert-manager --namespace cert-manager jetstack/cert-manager

Issuing certificates

cert-manager issues certificates from a CA such as Let’s Encrypt. It does this using the ACME protocol which supports various challenge mechanisms for verifying ownership of the domain.

Issuer

An Issuer or ClusterIssuer identifies which Certificate Authority cert-manager will use to issue a certificate. Issuer is a namespaced resource allowing you to use different CAs in each namespace, a ClusterIssuer is used to issue certificates in any namespace. Configuration depends on which ACME challenge you are using.

Certificate

A Certificate is a namespaced resource that references an Issuer or ClusterIssuer for issuing certificates. Certificates define the DNS name(s) a key and certificate should be issued for, as well as the secret to store those files (e.g. ambassador-certs). Configuration depends on which ACME challenge you are using.

By duplicating issuers, certificates, and secrets one can support multiple domains with SNI.

Challenge

cert-manager supports two kinds of ACME challenges that verify domain ownership in different ways: HTTP-01 and DNS-01.

DNS-01 challenge

The DNS-01 challenge verifies domain ownership by proving you have control over its DNS records. Issuer configuration will depend on your DNS provider. This example uses AWS Route53.

Create the IAM policy specified in the cert-manager AWS Route53 documentation.
Note the accessKeyID and create a secret named prod-route53-credentials-secret in the cert-manager namespace that has a key value: secret-access-key from your AWS IaM credentials.

Create and apply a ClusterIssuer.

---
apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
metadata:
  name: letsencrypt-prod
spec:
  acme:
    email: email@example.com
    server: https://acme-v02.api.letsencrypt.org/directory
    privateKeySecretRef:
      name: letsencrypt-prod
    solvers:
    - selector:
        dnsZones:
          - "myzone.route53.com"
      dns01:
        route53:
          region: us-east-1
          accessKeyID: {accessKeyID}
          hostedZoneID: {Hosted Zone ID} # optional, allows you to reduce the scope of permissions in Amazon IAM
          secretAccessKeySecretRef:
            name: prod-route53-credentials-secret
            key: secret-access-key

Create and apply a Certificate.

---
apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: myzone.route53.com
  # cert-manager will put the resulting Secret in the same Kubernetes
  # namespace as the Certificate. You should create the certificate in
  # whichever namespace you want to configure a Host.
spec:
  secretName: ambassador-certs
  issuerRef:
    name: letsencrypt-prod
    kind: ClusterIssuer
  commonName: myzone.route53.com
  dnsNames:
  - myzone.route53.com

Verify the secret is created.

$ kubectl get secrets -n ambassador
NAME                     TYPE                                  DATA      AGE
ambassador-certs         kubernetes.io/tls                     2         1h

HTTP-01 challenge

The HTTP-01 challenge verifies ownership of the domain by sending a request for a specific file on that domain. cert-manager accomplishes this by sending a request to a temporary pod with the prefix /.well-known/acme-challenge/. To perform this challenge:

Create and apply a ClusterIssuer.

---
apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
metadata:
  name: letsencrypt-prod
spec:
  acme:
    email: email@example.com
    server: https://acme-v02.api.letsencrypt.org/directory
    privateKeySecretRef:
      name: letsencrypt-prod
    solvers:
    - http01:
        ingress:
          class: nginx
      selector: {}

Create and apply a Certificate.

---
apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: ambassador-certs
  # cert-manager will put the resulting Secret in the same Kubernetes
  # namespace as the Certificate. You should create the certificate in
  # whichever namespace you want to configure a Host.
  namespace: ambassador
spec:
  secretName: ambassador-certs
  issuerRef:
    name: letsencrypt-prod
    kind: ClusterIssuer
  dnsNames:
  - example.com

Apply both the ClusterIssuer and Certificate

After applying both of these YAML manifests, you will notice that cert-manager has spun up a temporary pod named cm-acme-http-solver-xxxx but no certificate has been issued. Check the cert-manager logs and you will see a log message that looks like this:

$ kubectl logs cert-manager-756d6d885d-v7gmg
...
Preparing certificate default/ambassador-certs with issuer
Calling GetOrder
Calling GetAuthorization
Calling HTTP01ChallengeResponse
Cleaning up old/expired challenges for Certificate default/ambassador-certs
Calling GetChallenge
wrong status code '404'
Looking up Ingresses for selector certmanager.k8s.io/acme-http-domain=161156668,certmanager.k8s.io/acme-http-token=1100680922
Error preparing issuer for certificate default/ambassador-certs: http-01 self check failed for domain "example.com

Create a Mapping for the /.well-known/acme-challenge/ route.

cert-manager uses an Ingress to issue the challenge to /.well-known/acme-challenge/ that is incompatible with Ambassador. We will need to create a Mapping so the cert-manager can reach the temporary pod.

---
apiVersion: getambassador.io/v3alpha1
kind: Mapping
metadata:
  name: acme-challenge-mapping
spec:
  hostname: "*"
  prefix: /.well-known/acme-challenge/
  rewrite: ""
  service: acme-challenge-service

---
apiVersion: v1
kind: Service
metadata:
  name: acme-challenge-service
spec:
  ports:
  - port: 80
    targetPort: 8089
  selector:
    acme.cert-manager.io/http01-solver: "true"

Apply the YAML and wait a couple of minutes. cert-manager will retry the challenge and issue the certificate.

Verify the secret is created:

$ kubectl get secrets
NAME                     TYPE                                  DATA      AGE
ambassador-certs         kubernetes.io/tls                     2         1h
ambassador-token-846d5   kubernetes.io/service-account-token   3         2h

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Last modified July 1, 2024: Update AESproductName to Ambassador Edge Stack, productName to Emissary, and OSSproductName to Emissary (bdb5ad8)