Redirect Azure App Static url to my own using gateway

Question

I've setup our environment within app service plans along with all applications. I created a gateway within azure along with pointing my domain to azure. I'm now trying to setup a redirect that will go from the azure assigned URL for the app to my own. For example, azure assigns the URL,

abc.azurewebsites.net and I want it to instead go to dev.abc.com.

I'm missing something because I can successfully deploy my app from visual studio to the azure IP, and it works that way. But if I manually type the desired URL, it states.

<h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>

I've looked at the front door app and couldn't get that to work as desired either. Any guidance would be appreciated.

Answer 1

Hello @Steve Young ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you have an App service with Application gateway configured with your custom domain but on accessing the App via the Application gateway/Front Door, it is getting redirected to the App service URL and you would like to access it with your custom domain URL.

This URL redirection is a known issue with reverse proxy and multitenant PaaS services.

Multitenant PaaS services often require a registered and validated host name in order to route an incoming request to the appropriate tenant's back-end server. This is because there's typically a shared pool of load balancers that accept incoming requests for all tenants. The tenants commonly use the incoming host name to look up the correct back end for the customer tenant.

To make it easy to get started, these platforms typically provide a default domain that's preconfigured to route traffic to your deployed instance. For App Service, this default domain is azurewebsites.net. Each web app that you create gets its own subdomain, for example, contoso.azurewebsites.net.

Having a different host name at the reverse proxy (in your case, Application gateway/Front Door) than the one that's provided to the back-end application server can lead to cookies or redirect URLs that don't work properly. For example, session state can get lost, authentication can fail, or back-end URLs can inadvertently be exposed to end users. This is what is happening in your case.

The recommended solution for this issue is to preserve the original HTTP host name when you use a reverse proxy in front of a web application.

Refer: https://learn.microsoft.com/en-us/azure/architecture/best-practices/host-name-preservation#implementation-guidance-for-common-azure-services

Back-end configuration or the changes required on your web app/App service:

Since you are using an App Service, you can attach a custom domain name to the web app and avoid using the default azurewebsites.net host name towards the back end.

Refer: https://learn.microsoft.com/en-us/azure/architecture/best-practices/host-name-preservation#back-end-configuration

https://learn.microsoft.com/en-us/azure/static-web-apps/custom-domain-external

https://learn.microsoft.com/en-us/azure/app-service/app-service-web-tutorial-custom-domain?tabs=root%2Cazurecli

https://learn.microsoft.com/en-us/azure/app-service/manage-custom-dns-migrate-domain

Reverse proxy configuration or changes required on your Azure Application gateway/Front Door:

• If you use Application Gateway as the reverse proxy, you can ensure that the original host name is preserved by disabling Override with new host name on the back-end HTTP setting. Doing so disables both Pick host name from back-end address and Override with specific domain name. (Both of these settings override the host name.)
• If you use Azure Front Door Classic, you can avoid overriding the host name by leaving the back-end host header blank in the back-end pool definition.
• If you use Azure Front Door Standard or Premium, you can preserve the host name by leaving the origin host header blank in the origin definition.

Refer: https://learn.microsoft.com/en-us/azure/architecture/best-practices/host-name-preservation#reverse-proxy-configuration

https://learn.microsoft.com/en-us/azure/architecture/best-practices/host-name-preservation#azure-front-door

Once you make the above changes, your Azure Application gateway/Front Door custom domain URL will not redirect to the backend/origin (App service) host name URL anymore.

Refer the below docs for more details on this issue:

https://learn.microsoft.com/en-us/azure/application-gateway/troubleshoot-app-service-redirection-app-service-url

https://learn.microsoft.com/en-us/azure/architecture/best-practices/host-name-preservation#potential-issues

Kindly let us know if the above helps or you need further assistance on this issue.

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