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URL Redirect for Azure Application Gateway for Containers - Ingress 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. Any 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 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 IngressExtension resources

  1. Create an IngressExtension resource to handle HTTP to HTTPS redirect for contoso.com

    kubectl apply -f - <<EOF
apiVersion: alb.networking.azure.io/v1
kind: IngressExtension
metadata:
  name: http-to-https
  namespace: test-infra
spec:
  rules:
    - host: contoso.com
      requestRedirect:
        statusCode: 301
        scheme: https
EOF

  2. Create an IngressExtension resource to handle a path based redirect from contoso.com/summer-promotion to contoso.com/shop/category/5.

    kubectl apply -f - <<EOF
apiVersion: alb.networking.azure.io/v1
kind: IngressExtension
metadata:
  name: summer-promotion-redirect
  namespace: test-infra
spec:
  rules:
    - host: contoso.com
      requestRedirect:
        statusCode: 302
        path:
          type: ReplaceFullPath
          replaceFullPath: /shop/category/5
EOF

Deploy the required Ingress resources

  1. Create the first Ingress resource to listen for HTTPS requests.

    kubectl apply -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress-https
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
    alb.networking.azure.io/alb-frontend: ingress-fe
spec:
  ingressClassName: azure-alb-external
  tls:
    - hosts:
        - contoso.com
      secretName: listener-tls-secret
  rules:
    - host: contoso.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: echo
                port:
                  number: 80
EOF

  2. Create the second Ingress resource to listen on port 80 and redirect to HTTPS.

    kubectl apply -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress-http
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
    alb.networking.azure.io/alb-frontend: ingress-fe
    alb.networking.azure.io/alb-ingress-extension: http-to-https
spec:
  ingressClassName: azure-alb-external
  rules:
    - host: contoso.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: echo
                port:
                  number: 80
EOF

  3. Create a third Ingress resource to listen on port 80 and 443 for contoso.com/summer-promotion and redirect to contoso.com/shop/category/5.

    kubectl apply -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress-summer-promotion-redirect
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
    alb.networking.azure.io/alb-frontend: ingress-fe
    alb.networking.azure.io/alb-ingress-extension: summer-promotion-redirect
spec:
  ingressClassName: azure-alb-external
  tls:
    - hosts:
        - contoso.com
      secretName: listener-tls-secret
  rules:
    - host: contoso.com
      http:
        paths:
          - path: /summer-promotion
            pathType: Prefix
            backend:
              service:
                name: ignored-for-redirect
                port:
                  number: 80
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.

For each Ingress resource, ensure the status is valid, the listener is Programmed, and an address is assigned to the ingress resource. For all three Ingress resources, you should see the same hostname in this example.

kubectl get ingress ingress-https -n test-infra -o yaml

Example output of successful Ingress creation.

status:
  loadBalancer:
    ingress:
    - hostname: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.fzyy.alb.azure.com
      ports:
      - port: 443
        protocol: TCP

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 ingress ingress-http -n test-infra -o jsonpath='{.status.loadBalancer.ingress[0].hostname}')

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 Ingress API to configure both an HTTP to HTTPs redirect and path based redirection to specific client requests.