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Use certificates with LetsEncrypt.org on Application Gateway for AKS clusters

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This section configures your AKS to use LetsEncrypt.org and automatically obtain a TLS/SSL certificate for your domain. The certificate is installed on Application Gateway, which performs 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.

Tip

Also see What is Application Gateway for Containers.

Use the following steps to install cert-manager on your existing AKS cluster.

  1. Helm Chart

    Run the following script to install the cert-manager helm chart. The script performs the following actions:

    • creates a new cert-manager namespace on your AKS
    • creates the following CRDs: Certificate, Challenge, ClusterIssuer, Issuer, Order
    • installs cert-manager chart (from docs.cert-manager.io)
    #!/bin/bash

# Install the CustomResourceDefinition resources separately
kubectl apply -f https://github.com/cert-manager/cert-manager/releases/download/v1.10.1/cert-manager.crds.yaml

# 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 the cert-manager Helm chart
# Helm v3+
helm install \
  cert-manager jetstack/cert-manager \
  --namespace cert-manager \
  --version v1.10.1 \
  # --set installCRDs=true

# To automatically install and manage the CRDs as part of your Helm release,
# you must add the --set installCRDs=true flag to your Helm installation command.

  2. ClusterIssuer Resource

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

    Cert-manager uses the non-namespaced ClusterIssuer resource to 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 a certificate. More details on configuring ClusterIssuer properties here. ClusterIssuer instructs 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 following YAML is http01. Other challenges are documented on letsencrypt.org - Challenge Types

    Important

    Update <YOUR.EMAIL@ADDRESS> in the following YAML.

    #!/bin/bash
kubectl apply -f - <<EOF
apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: letsencrypt-staging
spec:
  acme:
    # You must replace this email address with your own.
    # Let's Encrypt uses 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 won't 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: example-issuer-account-key
    # 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:
              ingressclassName: azure/application-gateway
EOF

  3. Deploy App

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

    Ensure your 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). The annotation certmanager.k8s.io/cluster-issuer: letsencrypt-staging, which tells cert-manager to process the tagged Ingress resource.

    Important

    Update <PLACEHOLDERS.COM> in the following YAML 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
spec:
  tls:
  - hosts:
    - <PLACEHOLDERS.COM>
    secretName: guestbook-secret-name
  rules:
  - host: <PLACEHOLDERS.COM>
      http:
      paths:
      - backend:
          serviceName: frontend
          servicePort: 80
EOF

    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 certificate authority. The staging certificate is issued by CN=Fake LE Intermediate X1. This warning is an indication that the system worked as expected and you're ready for your production certificate.

  4. Production Certificate

    Once your staging certificate is set up successfully, you can switch to a production ACME server:

    1. Replace the staging annotation on your Ingress resource with: certmanager.k8s.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 previous ClusterIssuer YAML with https://acme-v02.api.letsencrypt.org/directory

  5. Certificate Expiration and Renewal

    Before the Lets Encrypt certificate expires, cert-manager automatically updates the certificate in the Kubernetes secret store. At that point, Application Gateway Ingress Controller applies the updated secret referenced in the ingress resources it's using to configure the Application Gateway.