Use Let's Encrypt certificates on Application Gateway for AKS clusters
You can configure your Azure Kubernetes Service (AKS) instance to use Let's Encrypt and automatically obtain a TLS/SSL certificate for your domain. The certificate is installed on Azure Application Gateway, which performs TLS/SSL termination for your AKS cluster.
The setup that this article describes uses the cert-manager Kubernetes add-on, which automates the creation and management of certificates.
Tip
Consider Application Gateway for Containers for your Kubernetes ingress solution.
Install the add-on
Use the following steps to install cert-manager on your existing AKS cluster:
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 cluster - Creates the following custom resource definitions (CRDs):
Certificate
,Challenge
,ClusterIssuer
,Issuer
,Order
- Installs the cert-manager chart (from the cert-manager site)
#!/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.
- Creates a new
Create a
ClusterIssuer
resource. Cert-manager requires this resource to represent the Let's Encrypt certificate authority that issues the signed certificate.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 particular domain name and to issue a certificate. You can get more details on configuringClusterIssuer
properties in the cert-manager documentation.ClusterIssuer
instructs cert-manager to issue certificates by using the Let's Encrypt staging environment that's used for testing. (The root certificate is not present in browser/client trust stores.)The default challenge type in the following YAML is
http01
. You can find other challenge types in the Let's Encrypt documentation.In the following YAML, be sure to replace
<YOUR.EMAIL@ADDRESS>
with your information.#!/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
Create an ingress resource to expose the
guestbook
application by using the Application Gateway deployment with the Let's Encrypt certificate.Ensure that your Application Gateway deployment has a public frontend IP configuration with a DNS name. Use the default
azure.com
domain, or provision an Azure DNS zone and then assign your own custom domain. The annotationcertmanager.k8s.io/cluster-issuer: letsencrypt-staging
tells cert-manager to process the tagged ingress resource.In the following YAML, be sure to replace
<PLACEHOLDERS.COM>
with your own domain or with the Application Gateway domain (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 by using the automatically issued Let's Encrypt certificate for staging.Your browser might warn you about an invalid certificate authority. The reason is that
CN=Fake LE Intermediate X1
issued the staging certificate. This warning means that the system worked as expected and you're ready for your production certificate.After you successfully set up your staging certificate, you can switch to a production ACME server:
- Replace the staging annotation on your ingress resource with
certmanager.k8s.io/cluster-issuer: letsencrypt-prod
. - Delete the existing staging
ClusterIssuer
resource that you created earlier. Create a new staging resource by replacing the ACME server from the previousClusterIssuer
YAML withhttps://acme-v02.api.letsencrypt.org/directory
.
- Replace the staging annotation on your ingress resource with
Before the Let's Encrypt certificate expires, cert-manager
automatically updates the certificate in the Kubernetes secret store. At that point, the Application Gateway Ingress Controller applies the updated secret referenced in the ingress resources that it's using to configure Application Gateway.