Cloudflare 520 error while Origin work fine (Enterprise support case not response yet)
Hi, Anyone had experienced Cloudflare got 520 error (and some client request timeout got 499)?
I checked on origin side everything work fine, firewall on origin allowed all of any public ip from cloudflare. Origin side work fine and tell us that cloudflare didn't send request to origin.
This problem occur around 1-2mins and I afraid that occur again without any prevention, those request really important to business for us.
3 Replies
Support AI
I'm happy to help you troubleshoot the issue.
Based on the Cloudflare documentation, Error 520 occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare. (Source: https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-520/)
Given that you've checked the origin side and everything seems fine, and the firewall allows all public IP addresses from Cloudflare, it's possible that the issue lies in the communication between Cloudflare and your origin server.
Here are a few potential causes mentioned in the documentation:
* Headers exceeding 16 KB (often due to excessive cookies)
* Empty or malformed responses lacking an HTTP status code or response body
* Missing response headers or origin web server not returning proper HTTP error responses
* Incorrect HTTP/2 configuration at the origin server
To troubleshoot further, you may want to check the following:
* Review your origin server's error logs to see if there are any errors or warnings related to the requests that timed out.
* Verify that your origin server is correctly configured to handle HTTP/2 connections, as Cloudflare connects to servers that announce support for HTTP/2 connections via ALPN.
* Check if there are any issues with your SSL/TLS configuration, as this can also cause errors.
If you're still unable to resolve the issue, you may want to provide more information about your setup and configuration to help further troubleshoot the problem.
Regarding the 499 error, it's a client request timeout error, which means that the client (in this case, Cloudflare) timed out waiting for a response from your origin server. This could be related to the same underlying issue causing the 520 error.
I hope this helps you get started on troubleshooting the issue. If you have any further questions or need more specific guidance, feel free to ask!
Sources
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I checked every well known issue on internet, but not match with my case. I'm not sure that every part on Cloudflare broken during that time? 2025-08-21 06:33 UTC
I'm joining you, I got the same error the day before yesterday. At first, everything was working smoothly, but then it suddenly crashed with a 520 error. Could it be because I'm in Russia?