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URL Redirect for Azure Application Gateway for Containers - Gateway API

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Application Gateway for Containers allows you to return a redirect response to the client based three aspects of a URL: protocol, hostname, and path. For each redirect, a defined HTTP status code may be returned to the client to define the nature of the redirect.

Usage details

URL redirects take advantage of the RequestRedirect rule filter as defined by Kubernetes Gateway API.

Redirection

A redirect sets the response status code returned to clients to understand the purpose of the redirect. The following types of redirection are supported:

  • 301 (Moved permanently): Indicates that the target resource is assigned a new permanent URI. Future references to this resource use one of the enclosed URIs. Use 301 status code for HTTP to HTTPS redirection.
  • 302 (Found): Indicates that the target resource is temporarily under a different URI. Since the redirection can change on occasion, the client should continue to use the effective request URI for future requests.

Redirection capabilities

  • Protocol redirection is commonly used to tell the client to move from an unencrypted traffic scheme to traffic, such as HTTP to HTTPS redirection.

  • Hostname redirection matches the fully qualified domain name (fqdn) of the request. This is commonly observed in redirecting an old domain name to a new domain name; such as contoso.com to fabrikam.com.

  • Path redirection has two different variants: prefix and full.

    • Prefix redirection type will redirect all requests starting with a defined value. For example: a prefix of /shop would match /shop and any text after. For example, /shop, /shop/checkout, and /shop/item-a would all redirect to /shop as well.
    • Full redirection type matches an exact value. For example: /shop could redirect to /store, but /shop/checkout wouldn't redirect to /store.

The following figure illustrates an example of a request destined for contoso.com/summer-promotion being redirected to contoso.com/shop/category/5. In addition, a second request initiated to contoso.com via http protocol is returned a redirect to initiate a new connection to its https variant.

A diagram showing the Application Gateway for Containers returning a redirect URL to a client.

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 deploy a sample TLS certificate to demonstrate redirect capabilities.

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

    This command creates the following on your cluster:

    • a namespace called test-infra
    • one service called echo in the test-infra namespace
    • one deployment called echo in the test-infra namespace
    • one secret called listener-tls-secret in the test-infra namespace

Deploy the required Gateway API resources

  1. 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: http-listener
    port: 80
    protocol: HTTP
    allowedRoutes:
      namespaces:
        from: Same
  - name: https-listener
    port: 443
    protocol: HTTPS
    allowedRoutes:
      namespaces:
        from: Same
    tls:
      mode: Terminate
      certificateRefs:
      - kind : Secret
        group: ""
        name: listener-tls-secret
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: Hostname
    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

Create an HTTPRoute resource for contoso.com that handles traffic received via https.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: https-contoso
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
    sectionName: https-listener
  hostnames:
  - "contoso.com"
  rules:
  - backendRefs:
    - name: echo
      port: 80
EOF

When the HTTPRoute resource is created, ensure the HTTPRoute resource shows Accepted and the Application Gateway for Containers resource is Programmed.

kubectl get httproute rewrite-example -n test-infra -o yaml

Verify the Application Gateway for Containers resource is successfully updated for each HTTPRoute.

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

Once the gateway is created, create an HTTPRoute resource for contoso.com with a RequestRedirect filter that redirects http traffic to https.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-to-https-contoso-redirect
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
    sectionName: http-listener
  hostnames:
  - "contoso.com"
  rules:
    - matches:
      filters:
        - type: RequestRedirect
          requestRedirect:
            scheme: https
            statusCode: 301
EOF

When the HTTPRoute resource is created, ensure the HTTPRoute resource shows Accepted and the Application Gateway for Containers resource is Programmed.

kubectl get httproute rewrite-example -n test-infra -o yaml

Verify the Application Gateway for Containers resource is successfully updated for each HTTPRoute.

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 an HTTPRoute resource for contoso.com that handles a redirect for the path /summer-promotion to a specific URL. By eliminating sectionName, demonstrated in the http to https HTTPRoute resources, this redirect rule applies to both HTTP and HTTPS requests.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: summer-promotion-redirect
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
    sectionName: https-listener
  hostnames:
  - "contoso.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /summer-promotion
    filters:
      - type: RequestRedirect
        requestRedirect:
          path:
            type: ReplaceFullPath
            replaceFullPath: /shop/category/5
          statusCode: 302
  - backendRefs:
    - name: echo
      port: 80
EOF

When the HTTPRoute resource is created, ensure the HTTPRoute resource shows Accepted and the Application Gateway for Containers resource is Programmed.

kubectl get httproute rewrite-example -n test-infra -o yaml

Verify the Application Gateway for Containers resource is successfully updated for each HTTPRoute.

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 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}')

When you specify the server name indicator using the curl command, http://contoso.com should return a response from the Application Gateway for Containers with a location header defining a 301 redirect to https://contoso.com.

fqdnIp=$(dig +short $fqdn)
curl -k --resolve contoso.com:80:$fqdnIp http://contoso.com/ -v

Via the response we should see:

* Added contoso.com:80:xxx.xxx.xxx.xxx to DNS cache
* Hostname contoso.com was found in DNS cache
*   Trying xxx.xxx.xxx.xxx:80...
* Connected to contoso.com (xxx.xxx.xxx.xxx) port 80 (#0)
> GET / HTTP/1.1
> Host: contoso.com
> User-Agent: curl/7.81.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 301 Moved Permanently
< location: https://contoso.com/
< date: Mon, 26 Feb 2024 22:56:23 GMT
< server: Microsoft-Azure-Application-LB/AGC
< content-length: 0
<
* Connection #0 to host contoso.com left intact

When you specify the server name indicator using the curl command, https://contoso.com/summer-promotion Application Gateway for Containers should return a 302 redirect to https://contoso.com/shop/category/5.

fqdnIp=$(dig +short $fqdn)
curl -k --resolve contoso.com:443:$fqdnIp https://contoso.com/summer-promotion -v

Via the response we should see:

> GET /summer-promotion HTTP/2
> Host: contoso.com
> user-agent: curl/7.81.0
> accept: */*
>
* TLSv1.2 (IN), TLS header, Supplemental data (23):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* old SSL session ID is stale, removing
* TLSv1.2 (IN), TLS header, Supplemental data (23):
* TLSv1.2 (OUT), TLS header, Supplemental data (23):
* TLSv1.2 (IN), TLS header, Supplemental data (23):
< HTTP/2 302
< location: https://contoso.com/shop/category/5
< date: Mon, 26 Feb 2024 22:58:43 GMT
< server: Microsoft-Azure-Application-LB/AGC
<
* Connection #0 to host contoso.com left intact

Congratulations, you have installed ALB Controller, deployed a backend application, and used Gateway API to configure both an HTTP to HTTPS redirect and path based redirection to specific client requests.