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Backend MTLS with Application Gateway for Containers - Gateway API

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This document helps set up an example application that uses the following resources from Gateway API. Steps are provided to:

  • Create a Gateway resource with one HTTPS listener.
  • Create an HTTPRoute resource that references a backend service.
  • Create a BackendTLSPolicy resource that has a client and CA certificate for the backend service referenced in the HTTPRoute.

Background

Mutual Transport Layer Security (MTLS) is a process that relies on certificates to encrypt communications and identify clients to a service. This enables backend workloads to further increase its security posture by only trusting connections from authenticated devices.

See the following figure:

A diagram showing the Application Gateway for Containers backend MTLS process.

Prerequisites

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

  2. If following the ALB managed deployment strategy, ensure you provision your ALB Controller and provision 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 and deploy sample secrets to demonstrate backend mutual authentication (mTLS).

    kubectl apply -f https://raw.githubusercontent.com/MicrosoftDocs/azure-docs/refs/heads/main/articles/application-gateway/for-containers/examples/https-scenario/end-to-end-ssl-with-backend-mtls/deployment.yaml

    This command creates the following on your cluster:

    • A namespace called test-infra
    • One service called mtls-app in the test-infra namespace
    • One deployment called mtls-app in the test-infra namespace
    • One config map called mtls-app-nginx-cm in the test-infra namespace
    • Four secrets called backend.com, frontend.com, gateway-client-cert, and ca.bundle in the test-infra namespace

Deploy the required Gateway API resources

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
spec:
  gatewayClassName: azure-alb-external
  listeners:
  - name: https-listener
    port: 443
    protocol: HTTPS
    allowedRoutes:
      namespaces:
        from: Same
    tls:
      mode: Terminate
      certificateRefs:
      - kind : Secret
        group: ""
        name: frontend.com
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

Once the gateway is created, create an HTTPRoute resource.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: https-route
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
  rules:
  - backendRefs:
    - name: mtls-app
      port: 443
EOF

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

kubectl get httproute https-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

Create a BackendTLSPolicy

kubectl apply -f - <<EOF
apiVersion: alb.networking.azure.io/v1
kind: BackendTLSPolicy
metadata:
  name: mtls-app-tls-policy
  namespace: test-infra
spec:
  targetRef:
    group: ""
    kind: Service
    name: mtls-app
    namespace: test-infra
  default:
    sni: backend.com
    ports:
    - port: 443
    clientCertificateRef:
      name: gateway-client-cert
      group: ""
      kind: Secret
    verify:
      caCertificateRef:
        name: ca.bundle
        group: ""
        kind: Secret
      subjectAltName: backend.com
EOF

Once the BackendTLSPolicy object is created, check the status on the object to ensure that the policy is valid:

kubectl get backendtlspolicy -n test-infra mtls-app-tls-policy -o yaml

Example output of valid BackendTLSPolicy object creation:

status:
  conditions:
  - lastTransitionTime: "2023-06-29T16:54:42Z"
    message: Valid BackendTLSPolicy
    observedGeneration: 1
    reason: Accepted
    status: "True"
    type: Accepted

Test access to the application

Now we're ready to send some traffic to our sample application, via the FQDN assigned to the frontend. Use the following command to get the FQDN:

fqdn=$(kubectl get gateway gateway-01 -n test-infra -o jsonpath='{.status.addresses[0].value}')

Curling this FQDN should return responses from the backend as configured on the HTTPRoute.

curl --insecure https://$fqdn/

Congratulations, you have installed ALB Controller, deployed a backend application and routed traffic to the application via the ingress on Application Gateway for Containers.