Linux Web App with AlwaysOn

Question

Hi

We're using Linux Web App with .NET 9.0. Running on P0v3 at least with 2 Instances using "Automatic" Scale out method.

We have AlwaysOn enabled. However, the application does not allow anonymous requests.

That means, every unauthenticated call to any endpoint, including root "/", will be anwered by the backend with an HTTP 302 to redirect the user to the IDP.

From the documentation, it was not clear to me whether this could be a problem.

Is this a problem for the “AlwaysOn” feature or the App Service in General if the Application answers with 302 ?

If so, is it possible to change the "AlwaysOn" Probe Endpoint for Linux App Services ?

Thanks

Answer 1

Hi @Stefan Geiger
This behavior is normal and does not mean there is an issue with the Always On feature or Azure App Service. With Always On enabled, the platform regularly sends an HTTP GET request to the root path ("/") of your application to keep it warm and responsive. If your app requires authentication and redirects unauthenticated requests, an HTTP 302 response is still valid because it shows the app and network are accessible. Always On does not need a 200 (OK) status code; it just requires a response without a timeout or server error (5xx). So, a 302 redirect will not stop the app from staying active.

Currently, Azure App Service on Linux does not let you change the Always On probe endpoint. The setting available for Windows App Service (like WEBSITE_ALWAYS_ON_PATH) is not supported on Linux, so the probe will keep targeting the root path. If your app blocks anonymous access, it’s a good practice to provide a lightweight health endpoint that allows anonymous requests and returns HTTP 200. While Always On cannot use a custom path on Linux, having a public health endpoint can help with monitoring and future integrations with load balancers or health checks.
https://learn.microsoft.com/en-us/azure/app-service/configure-common?tabs=portal
https://learn.microsoft.com/en-us/azure/app-service/monitor-instances-health-check?utm_source=chatgpt.com&tabs=dotnet
Let me know if you have any further assistances needed.