How to Fix Cloudflare’s “Error 520: Web Server Is Returning an Unknown Error”

What is Error 520?

A common mistake causing an empty or unexpected response to the original server is the Cloudflare 520 error. This is especially true that a resource-intensive procedure prevents the server from sending a prompt answer.

There are various other 5XX errors too, including the 502 bad gateway error, but they are highly different from one another in many ways.

When an empty, unknown or unexpected Cloudflare response is returned from the source server, the Cloudflare error 520 triggers. When more resources than a program, cron job, or resource are required, the Server may not be able to answer all requests correctly.

This produces the following: “Error 520: Web server is returning an unknown error.”

This mistake could be justified by:

• The web server application source crashes: The web server application crash at the server source is one of the main causes of this problem. The most likely reason for this is the running of a resource-intensive script. As a consequence, the server cannot reply in a timely manner to requests.
• No Cloudflare IPs allowed at the origin: the firewall of the original server may present an impediment when connecting to a non-whitelisted IP address. Therefore, if the IP address of Cloudflare is not whitelisted, the 529 error can occur.
• The origin of the TCP idle web server takes less than 300 seconds: A network connection is set up and maintained through the TCP protocol. The unknown error can be caused if its timeout value is too low.
• Headers above the header size limit of Cloudflare (8kb): The immense use of cookies or the use of large cookies increases headers’ size. Crossing the memory limit also causes other errors apart from 520 errors, including Since the header limit of Cloudflare exists at 8kb, the header cannot be processed.
• Empty reply from a web server that lacks an HTTP status or reply body: this is usually done when the domain DNS points to a faulty server.

Step 1: Log in to Cloudflare to start. Find and click on your website on the list.

Step 2: Next, pick the DNS tab, then click the Proxy Status section on the Orange Cloud. You’re going to know that Cloudflare was off as the visible cloud became grey.

Fix 2: Pausing the Cloudflare.

After logging in, you can also choose to pause Cloudflare.

Step 1: From the list, select your connected site.

Step 2: Then, in the sidebar, scroll down until you see the Advanced Actions area. To stop Cloudflare from running on your site, click the Stop Cloudflare on the Site link.

Step 3: On the website, you’ll see a pop-up asking you to confirm that you wish to pause Cloudflare. Don’t hesitate to click the Confirm button.

Step 1: Click the Caching tab towards the top of the screen after login into Cloudflare.

Step 2: After that, scroll down to the Development Mode area and flip the Off switch. “On” should now appear.

If you’re unsure where to find your error logs, contact your web host provider. You can utilize the procedures below if your hosting provider uses cPanel.

Step 1: Go to the Metrics area of the dashboard after logging into cPanel. Then select Errors from the drop-down menu.

Step 2: The error log page shows errors in reverse chronological order, the most recent 300 messages. If you or your host changed the settings, the error log may show more errors.

Because it compares response headers from the origin server and Cloudflare when it’s used as a proxy, it can aid debugging. It’s also used to check if the headers are too large, which could be the cause of error 520. The methods below will show you how to produce a HAR file using your browser:

Step 1: Right-click on the page in your browser. Then choose Inspect.

Step 2: After the panel has opened, go to the Network tab and look for a red circle button on the upper left-hand side of the screen. Click it if it’s grey.

Step 3: Click the clear button after checking the Preserve log option next to the record button.Step 4: Reload the page that is causing the 520 problems. Then right-click anywhere in the Chrome developer tool’s messages section.Step 5: Save the file on your computer by selecting Save as HAR with Content.

Step 1: When the error occurred, provide the full URL(s) to the support team.

Step 2: The Ray ID of Cloudflare from the website where the error 520 messages appeared.

If you’re still having problems after attempting these steps, you should contact your web hosting provider for further help.