Certificate issuance with LetsEncrypt.org

NOTE: Application Gateway for Containers has been released, which introduces numerous performance, resilience, and feature changes. Please consider leveraging Application Gateway for Containers for your next deployment.

This section configures your AKS to leverage LetsEncrypt.org and automatically obtain a TLS/SSL certificate for your domain. The certificate will be installed on Application Gateway, which will perform SSL/TLS termination for your AKS cluster. The setup described here uses the cert-manager Kubernetes add-on, which automates the creation and management of certificates.

Follow the steps below to install cert-manager on your existing AKS cluster.

Helm Chart

Run the following script to install the cert-manager helm chart. This will:

create a new cert-manager namespace on your AKS
create the following CRDs: Certificate, Challenge, ClusterIssuer, Issuer, Order
install cert-manager chart (from docs.cert-manager.io)

# Install the CustomResourceDefinition resources separately
# Note: --validate=false is required per https://github.com/jetstack/cert-manager/issues/2208#issuecomment-541311021
kubectl apply -f https://raw.githubusercontent.com/jetstack/cert-manager/release-0.13/deploy/manifests/00-crds.yaml --validate=false

# Create the namespace for cert-manager
kubectl create namespace cert-manager

# Label the cert-manager namespace to disable resource validation
kubectl label namespace cert-manager cert-manager.io/disable-validation=true

# Add the Jetstack Helm repository
helm repo add jetstack https://charts.jetstack.io

# Update your local Helm chart repository cache
helm repo update

# Install v0.11 of cert-manager Helm chart
helm install cert-manager \
  --namespace cert-manager \
  --version v0.13.0 \
  jetstack/cert-manager

ClusterIssuer Resource

Create a ClusterIssuer resource. It is required by cert-manager to represent the Lets Encrypt certificate authority where the signed certificates will be obtained.

By using the non-namespaced ClusterIssuer resource, cert-manager will issue certificates that can be consumed from multiple namespaces. Let’s Encrypt uses the ACME protocol to verify that you control a given domain name and to issue you a certificate. More details on configuring ClusterIssuer properties here. ClusterIssuer will instruct cert-manager to issue certificates using the Lets Encrypt staging environment used for testing (the root certificate not present in browser/client trust stores).

The default challenge type in the YAML below is http01. Other challenges are documented on letsencrypt.org - Challenge Types

IMPORTANT: Update <YOUR.EMAIL@ADDRESS> in the YAML below

kubectl apply -f - <<EOF
apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
metadata:
  name: letsencrypt-staging
spec:
  acme:

    # You must replace this email address with your own.
    # Let's Encrypt will use this to contact you about expiring
    # certificates, and issues related to your account.
    email: <YOUR.EMAIL@ADDRESS>

    # ACME server URL for Let’s Encrypt’s staging environment.
    # The staging environment will not issue trusted certificates but is
    # used to ensure that the verification process is working properly
    # before moving to production
    server: https://acme-staging-v02.api.letsencrypt.org/directory

    privateKeySecretRef:
      # Secret resource used to store the account's private key.
      name: letsencrypt-secret

    # Enable the HTTP-01 challenge provider
    # you prove ownership of a domain by ensuring that a particular
    # file is present at the domain
    solvers:
    - http01:
        ingress:
            class: azure/application-gateway
EOF

Deploy App

Create an Ingress resource to Expose the guestbook application using the Application Gateway with the Lets Encrypt Certificate.

Ensure you Application Gateway has a public Frontend IP configuration with a DNS name (either using the default azure.com domain, or provision a Azure DNS Zone service, and assign your own custom domain). Note the annotation cert-manager.io/cluster-issuer: letsencrypt-staging, which tells cert-manager to process the tagged Ingress resource.

IMPORTANT: Update <PLACEHOLDERS.COM> in the YAML below with your own domain (or the Application Gateway one, for example 'kh-aks-ingress.westeurope.cloudapp.azure.com')
```
kubectl apply -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: guestbook-letsencrypt-staging
annotations:
    kubernetes.io/ingress.class: azure/application-gateway
    cert-manager.io/cluster-issuer: letsencrypt-staging
    cert-manager.io/acme-challenge-type: http01
spec:
tls:
- hosts:
    - <PLACEHOLDERS.COM>
    secretName: guestbook-secret-name
rules:
- host: <PLACEHOLDERS.COM>
    http:
    paths:
    - backend:
        service:
            name: frontend
            port:
                number: 80
EOF
```
Use kubectl describe clusterissuer letsencrypt-staging to view the state of status of the ACME account registration. Use kubectl get secret guestbook-secret-name -o yaml to view the certificate issued.

After a few seconds, you can access the guestbook service through the Application Gateway HTTPS url using the automatically issued staging Lets Encrypt certificate. Your browser may warn you of an invalid cert authority. The staging certificate is issued by CN=Fake LE Intermediate X1. This is an indication that the system worked as expected and you are ready for your production certificate.
Production Certificate Once your staging certificate is setup successfully you can switch to a production ACME server:
1. Replace the staging annotation on your Ingress resource with: cert-manager.io/cluster-issuer: letsencrypt-prod
2. Delete the existing staging ClusterIssuer you created in the previous step and create a new one by replacing the ACME server from the ClusterIssuer YAML above with https://acme-v02.api.letsencrypt.org/directory
Certificate Expiration and Renewal Before the Lets Encrypt certificate expires, cert-manager will automatically update the certificate in the Kubernetes secret store. At that point, Application Gateway Ingress Controller will apply the updated secret referenced in the ingress resources it is using to configure the Application Gateway.