Need some help for Azure Front Door issue.

Hi Eric Gao,

Thanks for reaching out in Microsoft Q&A forum,

When your site uses Azure Front Door and suddenly starts returning 504 errors, it means that AFD is routing traffic to your backend (for example an App Service, VM, or AKS), but the backend either takes too long to respond or doesn’t respond at all. The 504 is essentially AFD saying, “I asked the server, but I didn’t get a proper answer in time, so I’m giving up and returning this error.”

Where to look first

• Check backend performance Bypass Front Door and hit the backend directly (use the backend URL or IP). If it’s slow or hangs, AFD will time out and return 504. Look at logs from your app, database, or any downstream APIs to see if requests are taking longer than 30 seconds.
• Check backend health in AFD In the Azure portal, go to your Front Door profile → Backend pools → see if the backend shows as Unhealthy or intermittent health. If health probes fail, AFD may stop routing traffic or fall back to a slower path, which can also cause 504s.
• Review AFD timeout settings The default origin response timeout is 30 seconds. If your backend realistically needs more time (for example 60–120 seconds), you can increase the Origin response timeout in the Front Door profile (Standard/Premium SKUs) up to 240 seconds. This reduces 504s without changing your app code.
• Check network and security Make sure NSG rules, firewalls, WAF, or load balancers are not blocking or delaying traffic from AFD’s POPs. If AFD is routed through a private link or VNet, ensure the Private Endpoint is approved and connected.
• Use logs and ErrorInfo Look at AFD’s diagnostics / Front Door Analytics logs and filter for 504 responses plus the ErrorInfo field. If it shows OriginTimeout, you know the backend simply took too long and you either need to optimize the backend or increase the timeout.

Reference:

• Troubleshoot common issues - Azure Front Door | Microsoft Learn
• Configure Azure Front Door Logs | Microsoft Learn

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

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