Fixing Error 520 on Cloudflare Quickly and Easily

If you're managing a website that uses Cloudflare's content delivery network (CDN), you may have come across the dreaded Error 520: Web Server Is Returning an Unknown Error. It's one of the more frustrating HTTP errors because it doesn’t offer much detail about what's gone wrong. But don’t worry—while this error can be perplexing at first glance, fixing it is often easier than it appears.

In this article, we’ll explore what Cloudflare Error 520 actually means, why it occurs, and how you can quickly and easily resolve it. Whether you're a site administrator or a developer, you’ll find the information here practical and to-the-point.

What is Cloudflare Error 520?

Error 520 occurs when Cloudflare makes a successful connection to the origin web server, but it receives an unexpected or invalid response from that server. In essence, Cloudflare acts as a middleman between the user and your server. When it fails to understand or handle your server’s response, you’ll see a 520 error.

This error usually arises due to server-side issues such as configuration problems, crashes, or firewall settings silently blocking requests from Cloudflare.

Common Causes of Error 520

Before diving into solutions, understanding the root causes is crucial. Below are the most common reasons for a 520 error:

• Server crashes or resource limitations (e.g. out of memory)
• Malformed HTTP headers or empty responses
• Firewall or security software blocking Cloudflare’s IPs
• Keep-Alive or time-out settings misconfigured
• Origin server not properly handling SSL/TLS connections
• Request overload, where too many requests flood your origin server

How to Fix Error 520 Quickly and Easily

Let’s walk through simple and effective steps to troubleshoot and resolve Error 520. You don’t have to be a server wizard to follow this guide. Just take it step by step.

1. Restart Your Web Server

Sometimes all your server needs is a reboot. Rebooting can fix temporary issues such as high memory usage or process misbehavior.

Steps:

1. Log into your server via SSH or your hosting control panel.
2. Restart your web server (Apache, Nginx, etc.). For example:
   sudo systemctl restart apache2 or sudo systemctl restart nginx

This step alone often resolves the 520 error, especially when the cause is a temporary server crash.

2. Check Error Logs for Clues

Your server logs are filled with clues. Review them to identify what went wrong right before the 520 error began appearing.

Files to check:

• Apache logs: /var/log/apache2/error.log
• Nginx logs: /var/log/nginx/error.log
• Application logs depending on your framework (e.g., Laravel, Django)

Look for spikes in activity, PHP errors, or memory limit issues.

3. Disable or Adjust Firewall/Security Tools

Cloudflare connects from its own set of IP addresses. Firewalls or security applications like mod_security, fail2ban, or third-party plugins can mistakenly block these IPs.

Solutions:

• Whitelist Cloudflare IPs in your firewall or host settings.
• Temporarily disable controversial security rules, especially those related to HTTP headers.
• Review intrusion prevention logs that may show blocked requests from Cloudflare IPs.

You can find a list of Cloudflare’s IP ranges on their official documentation. Always make sure these aren’t being blocked.

4. Review and Fix HTTP Headers

If your server is sending malformed or oversized headers, Cloudflare may reject the response. Make sure your headers conform to HTTP RFC standards.

Also, ensure that your application isn’t sending duplicate or non-printable characters as headers. These are common in custom-coded APIs or misconfigured CMS systems.

5. Increase Server Resource Limits

In shared hosting or budget VPS environments, your server might run out of memory or CPU resources. This leads to timeouts or empty responses.

What to do:

• Monitor your server’s memory and CPU usage with tools like top or htop.
• If you're on shared hosting, contact your provider to increase limits or consider upgrading to a plan with more resources.

6. Test with cURL

Use cURL to replicate what Cloudflare is doing and spot inconsistencies in the server’s response.

curl -I http://yourdomain.com

If you see slow responses, unexpected errors, or no response at all, your server is likely the culprit.

7. Temporarily Disable Cloudflare

To confirm whether Cloudflare is the problem or just the messenger, pause Cloudflare and check if the site works directly through your origin server.

To pause Cloudflare:

• Go to your Cloudflare dashboard
• Navigate to your domain settings
• Select “Pause Cloudflare on Site” under “Advanced Actions”

Visit your site without Cloudflare. If the problem persists, then it’s your server. If it disappears, Cloudflare settings may need closer inspection.

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8. Contact Your Hosting Provider

If you've gone through the steps above and still can't find the issue, it might be time to talk to your hosting provider. They can access logs you can’t, or help you identify an underlying infrastructure issue.

9. Contact Cloudflare Support

If you suspect it’s a bug or issue on the Cloudflare side—especially if the error only happens occasionally or during specific requests—reach out to their support team.

Include these in your ticket:

• Your site URL
• Time and date of the error
• Ray ID (found at the bottom of the Cloudflare error page)
• Trace logs from your web server, if available

Preventive Measures for the Future

Once you’ve resolved the 520 error, it’s a good idea to adopt best practices that help you avoid running into it again.

• Regular server updates: Keep your web server, CMS, and plugins up to date.
• Use uptime monitoring tools: Tools like UptimeRobot or Pingdom can alert you early when problems arise.
• Error logging tools: Implement robust error tracking tools like Sentry or LogRocket.
• Optimize server response time: Reduce heavy operations in backend code and limit unnecessary database queries.
• Monitor firewall activity: Set regular alerts for blocked IP addresses or suspicious behavior.

Conclusion

Cloudflare's Error 520 can feel vague and intimidating, but it’s usually a server-side hiccup that can be resolved quickly with the right approach. From reviewing error logs to temporarily disabling Cloudflare, you have multiple tools at your disposal to fix the issue and keep your website running smoothly.

The key is not to panic. Work methodically through the potential causes, and in no time, you'll have your site back up and error-free.

Remember, every error is a chance to make your server configuration more robust and secure. Happy troubleshooting!