Error 520 Unknown Error

Mainton Company - IT solutions for business since 2004

This article will talk about what Error 520 Unknown Error is. It indicates that the CloudFlare system cannot process the response from the web server on which the site is located.

There are special services to monitor the online status of a site and assess site accessibility. One of these services is the BAILRY service – a free regular (periodic) website accessibility check. This service also has a paid subscription for constant monitoring of site availability.

The most common causes of the error:

  • connection reset (after a successful request, the server closed the connection);
  • the request header exceeds the Cloudflare header size limit (more than 8 KB);
  • empty response from the server;
  • incorrect response from the server.

Recommendations for fixing 520 Unknown Error

Contact your hosting provider or site administrator and request a review of your origin web server’s error logs for failures and look out for the following common causes:

  • The Origin web server application crashes
  • Cloudflare IPs are not allowed
  • Origin web server TCP idle timeout shorter than 300 seconds
  • Headers larger than 8 KB (usually due to too many cookies)
  • An empty response from the origin web server that has no HTTP status code or response body
  • Response headers are missing or the original web server is not returning correct HTTP error responses

Error 520 is common in some PHP applications that cause the original web server to crash.

If Error 520 continues after contacting your hosting provider or site administrator, please provide the following information to Cloudflare Support:

  • Full URL of the resource requested when the error occurred
  • Cloudflare cf-request-id or cf-ray from error message 520
  • Output from (replace with your hostname and domain where the 520 error occurred)
  • Two HAR files:
    • one with Cloudflare enabled on your site, and
    • another with Cloudflare temporarily disabled

Finally, it is important to note that the trust of clients and users in your website, as well as your position in search engines, directly depend on the availability of your resource (website) at any given time.

And you can control this availability using the BAILRY service – a unique software product that has no analogues on the market. To stay informed, sign up for a free regular (periodic) website accessibility check today!