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Cert-manager and Let's Encrypt with Application Gateway for Containers - Gateway API

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This guide demonstrates how to use cert-manager to automatically issue and renew SSL/TLS certificates to one or more frontends of your Azure Application Gateway for Containers deployment. We use the Gateway API to configure the necessary resources.

For the purposes of this example, we have cert-manager configure certificates issued from Let's Encrypt to demonstrate an end-to-end deployment, where Application Gateway for Containers is providing TLS offloading.

A figure showing cert-manager retrieving a certificate from Let's Encrypt and storing it into Kubernetes' secret store for TLS with Application Gateway for Containers.

For certificates to be issued by Let's Encrypt, a challenge is required by the authority to validate domain ownership. This validation happens by allowing cert-manager to create a pod and HTTPRoute resource that exposes an endpoint during certificate issuance, proving your ownership of the domain name.

More details on cert-manager and Let's Encrypt with AKS in general may be found here.

Prerequisites

  1. If following the BYO deployment strategy, ensure that you set up your Application Gateway for Containers resources and ALB Controller

  2. If following the ALB managed deployment strategy, ensure that you provision your ALB Controller and the Application Gateway for Containers resources via the ApplicationLoadBalancer custom resource.

  3. Deploy sample HTTP application Apply the following deployment.yaml file on your cluster to create a sample web application to demonstrate the header rewrite.

    kubectl apply -f https://learn.microsoft.com/azure/application-gateway/for-containers/examples/traffic-split-scenario/deployment.yaml

    This command creates the following on your cluster:

    • a namespace called test-infra
    • two services called backend-v1 and backend-v2 in the test-infra namespace
    • two deployments called backend-v1 and backend-v2 in the test-infra namespace

Create a Gateway resource

Create a new Gateway resource that listens for HTTP requests from Let's Encrypt during the challenge process.

Create a gateway:

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: gateway-01
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
    cert-manager.io/issuer: letsencrypt-cert
spec:
  gatewayClassName: azure-alb-external
  listeners:
  - name: http-listener
    protocol: HTTP
    port: 80
    allowedRoutes:
        namespaces:
          from: Same
EOF

Note

When the ALB Controller creates the Application Gateway for Containers resources in ARM, it'll use the following naming convention for a frontend resource: fe-<8 randomly generated characters>

If you would like to change the name of the frontend created in Azure, consider following the bring your own deployment strategy.

Once the gateway resource is created, ensure the status is valid, the listener is Programmed, and an address is assigned to the gateway.

kubectl get gateway gateway-01 -n test-infra -o yaml

Example output of successful gateway creation.

status:
  addresses:
  - type: IPAddress
    value: xxxx.yyyy.alb.azure.com
  conditions:
  - lastTransitionTime: "2023-06-19T21:04:55Z"
    message: Valid Gateway
    observedGeneration: 1
    reason: Accepted
    status: "True"
    type: Accepted
  - lastTransitionTime: "2023-06-19T21:04:55Z"
    message: Application Gateway For Containers resource has been successfully updated.
    observedGeneration: 1
    reason: Programmed
    status: "True"
    type: Programmed
  listeners:
  - attachedRoutes: 0
    conditions:
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: ""
      observedGeneration: 1
      reason: ResolvedRefs
      status: "True"
      type: ResolvedRefs
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: Listener is accepted
      observedGeneration: 1
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: Application Gateway For Containers resource has been successfully updated.
      observedGeneration: 1
      reason: Programmed
      status: "True"
      type: Programmed
    name: https-listener
    supportedKinds:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute

Install Cert-Manager

Install cert-manager using Helm:

helm repo add jetstack https://charts.jetstack.io --force-update
helm install \
  cert-manager jetstack/cert-manager \
  --namespace cert-manager \
  --create-namespace \
  --version v1.16.0 \
  --set config.enableGatewayAPI=true \
  --set crds.enabled=true

The helm installation creates three deployments and some services and pods in a new namespace called cert-manager. It also installs cluster-scoped supporting resources, such as RBAC roles and Custom Resource Definitions.

Create a ClusterIssuer

Create a ClusterIssuer resource to define how cert-manager will communicate with Let's Encrypt. For this example, an HTTP challenge is used. During challenge, cert-manager creates an HTTPRoute resource and corresponding pod presenting a validation endpoint to prove ownership of the domain.

Tip

Other challenges supported by Let's Encrypt are documented on letsencrypt.org - Challenge Types

kubectl apply -f - <<EOF
apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: letsencrypt-prod
  namespace: test-infra
spec:
  acme:
    server: https://acme-v02.api.letsencrypt.org/directory # production endpoint
    #server: https://acme-staging-v02.api.letsencrypt.org/directory # staging endpoint
    email: your-email@example.com
    privateKeySecretRef:
      name: letsencrypt-private-key
    solvers:
      - http01:
          gatewayHTTPRoute:
            parentRefs:
              - name: gateway-01
                namespace: test-infra
                kind: Gateway
EOF

Verify the resource was created

kubectl get ClusterIssuer -A -o yaml

The status should show True and type Ready.

  status:
    acme:
      lastPrivateKeyHash: x+xxxxxxxxxxxxxxxxxxxxxxx+MY4PAEeotr9XH3V7I=
      lastRegisteredEmail: your-email@example.com
      uri: https://acme-staging-v02.api.letsencrypt.org/acme/acct/165888253
    conditions:
    - lastTransitionTime: "2024-10-04T21:22:40Z"
      message: The ACME account was registered with the ACME server
      observedGeneration: 1
      reason: ACMEAccountRegistered
      status: "True"
      type: Ready

Create a certificate

kubectl apply -f - <<EOF
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: letsencrypt-cert
  namespace: test-infra
spec:
  secretName: letsencrypt-secret # name published to secret store
  issuerRef:
    name: letsencrypt-prod # ClusterIssuer resource name
    kind: ClusterIssuer
  dnsNames:
    - contoso.com # domain name to be used
EOF

Execute the following command to validate issuance of the certificate. If the certificate has been issued, the value of the READY column should be True.

kubectl get certificate letsencrypt-cert -n test-infra

If the certificate wasn't issued, you can execute the following command to validate the status of a challenge.

Note

If the certificate has been successfully issued, the challenge will no longer be listed.

kubectl get challenges -n test-infra -o yaml

Enable HTTPS on the Gateway resource

Modify the gateway to add a second listener to terminate HTTPS requests with the issued Let's Encrypt certificate.

Create a gateway:

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: gateway-01
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
    cert-manager.io/issuer: letsencrypt-cert
spec:
  gatewayClassName: azure-alb-external
  listeners:
  - name: http-listener
    protocol: HTTP
    port: 80
    allowedRoutes:
        namespaces:
          from: Same
  - name: https-listener
    port: 443
    protocol: HTTPS
    tls:
      certificateRefs:
      - name: letsencrypt-secret
    allowedRoutes:
      namespaces:
        from: Same
EOF

Note

When the ALB Controller creates the Application Gateway for Containers resources in ARM, it'll use the following naming convention for a frontend resource: fe-<8 randomly generated characters>

If you would like to change the name of the frontend created in Azure, consider following the bring your own deployment strategy.

Create a HTTPRoute that listens for your hostname

Create a HTTPRoute to handle requests received by the https-listener listener.

Important

Ensure you replace contoso.com with the domain name you are expecting the certificate to be issued to.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: https-example
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
  hostnames:
  - "contoso.com"
  rules:
  - backendRefs:
    - name: backend-v1
      port: 8080
EOF

Once the HTTPRoute resource is created, ensure the route is Accepted and the Application Gateway for Containers resource is Programmed.

kubectl get httproute cert-manager-route -n test-infra -o yaml

Verify the status of the Application Gateway for Containers resource is successfully updated.

status:
  parents:
  - conditions:
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: ""
      observedGeneration: 1
      reason: ResolvedRefs
      status: "True"
      type: ResolvedRefs
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: Route is Accepted
      observedGeneration: 1
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: Application Gateway For Containers resource has been successfully updated.
      observedGeneration: 1
      reason: Programmed
      status: "True"
      type: Programmed
    controllerName: alb.networking.azure.io/alb-controller
    parentRef:
      group: gateway.networking.k8s.io
      kind: Gateway
      name: gateway-01
      namespace: test-infra

Test access to the application

Now we're ready to send some traffic to our sample application, via the hostname used for your certificate.

Important

Ensure you replace contoso.com with the domain name you are expecting the certificate to be issued to.

curl https://contoso.com/ -v 2>&1 | grep issuer

Upon result, you should see

* issuer: C=US; O=Let's Encrypt; CN=R10

Congratulations, you have installed ALB Controller, deployed a backend application, issued a certificate from Let's Encrypt with cert-manager, and routed traffic to the application via Application Gateway for Containers.