Azure App Gateway - Backend Health 404 error

Question

I am trying to configure Azure Application Gateway with ADFS. The Backend pool points to ADFS Web Application Proxy. The backend health check is reporting as unhealthy. I am getting an a error: received invalid status code 404 in the backend servers http response

Everything appears to be configured correctly and I can access the site when bypassing the App Gateway

Answer 1

This was resolved by re-configuring the health probe

Answer 2

In my case with the App Service as a backend pool, I had to create a custom Health probe(http-probe for ex.) to be used in the HTTP setting(http for ex.), where the HTTP setting(http for ex.) is the one configured in the Request Routing Rule.