How to diagnose random Azure FrontDoor 503 errors

Question

Hi there,

I have FrontDoor setup in front of multiple backend Web App. I've noticed there's a number of random 503 errors each day. The requests themselves are valid, and retrying generally works, however, the initial request that fails is not hitting the backend Web App. The backend health at the times of the errors are also 100%, and it can't be a timeout because the error is immediate (timeout is also extended to 240 seconds). It seems like FrontDoor itself is having some kind of health issue, but there's no health issues mentioned.

After doing some research, I've increased the timeout to 240 and also remove accept-encoding from the request for byte range requests as recommended in the link provided below,

https://learn.microsoft.com/en-us/azure/frontdoor/front-door-troubleshoot-routing

However, still a number of random 503 errors/blank page each day is showing out.

Please advise.

Thank you.

Answer 1

We've been experiencing the exact same issue but Azure support hasn't been of much help and has been rather dismissive of the issue.

Answer 2

@Daniel Lee , Apologies for the inconvenience caused. Looks like you have implemented all the client side checks for 503 error. Now, we will check if there are any server-side issues raised here, for that you need to provide us with the actual tracking ID or GUID on top of that web page along with your subscription. Please do mail these details to azcommunity@microsoft.com for further insights.

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