Thank you for reaching out.
I understand you have a single App Service as a backend of your Azure Front Door and in the Health probe logs you keep getting result: OriginError with a 301 status code as well.
I think this is expected because for Azure Front Door Healthprobe as documented here a 200 OK status code indicates the origin is healthy. Any other status code is considered a failure. As the health probe is getting a 301 response hence the backend is marked as unavailable.
A quick fix here will be to change the path of the health probe which will return a 200 response when the App Service is healthy.
As per the best practices document here It's usually a good idea to monitor a webpage or location that you specifically design for health monitoring. Your application logic can consider the status of all of the critical components required to serve production traffic including application servers, databases, and caches.
Hope this helps! Please let me know if you have any additional questions. Thank you!
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