What is a 520 error? Causes and fixes

Key highlights 

• A 520 error occurs when Cloudflare receives an unexpected response from the origin server. 
• Common causes include server misconfigurations, connection resets and blocked Cloudflare IPs. 
• Fixing a 520 error involves checking server logs, adjusting response headers and whitelisting Cloudflare IPs. 
• Restarting web services, reviewing DNS settings and disabling .htaccess can help resolve the issue. 
• Regular server maintenance, monitoring logs and optimizing timeout settings can prevent future errors. 
• Upgrading to a reliable hosting provider can minimize server-related issues and improve uptime. 

Introduction 

Imagine this: a potential customer visits your website, eager to explore your offerings, but instead of the website loading smoothly, he’s met with a 520 error. Frustrated, he leaves—and just like that, you’ve lost a visitor, maybe even a sale. 

A 520 error can be a silent killer of website performance, disrupting traffic and damaging user trust. This Cloudflare-specific error occurs when the origin server sends an unexpected or incomplete response, leaving website owners scrambling for answers. This ultimately harms user trust and conversions. But don’t worry, we’ve got your back. 

 This blog will act as a guide to help you break down the causes of 520 error and provide fixes to keep your website running smoothly. 

What is a 520 error? 

A 520 error is a Cloudflare-specific HTTP status code that indicates the web server returned with an unknown or unexpected response. This typically happens when Cloudflare, acting as a proxy, cannot establish a stable connection with the origin server. Unlike a traditional 5xx error, which usually pinpoints a specific issue, the 520 error is more generic, making troubleshooting slightly more complex. 

Common causes of a 520 error 

1. Unexpected server responses 

If the origin server responds with an invalid or corrupted HTTP header, Cloudflare may not recognize the response, leading to a Cloudflare 520 error. This can occur due to improper server configuration, outdated software or misconfigured firewall rules blocking certain requests. Ensuring that HTTP headers are correctly formatted and that necessary configurations are updated can help mitigate this issue. 

2. Connection resets 

A connection reset occurs when the origin server abruptly closes the connection before a complete response is sent to Cloudflare. This could be caused by server overload, a misconfigured TCP timeout setting or an issue with the hosting provider’s network. Checking server logs and adjusting timeout settings can help resolve this problem. 

3. Large or malformed HTTP response headers 

When response headers exceed Cloudflare’s allowed limits or contain incorrect formatting, Cloudflare may reject them, triggering a 520 error. This can be caused by plugins or applications generating excessive data in headers.  

4. Empty or no response from the server 

If Cloudflare requests a resource and the server returns an empty response, it results in a Cloudflare 520 error since it expects a valid HTTP reply. This may happen due to a server crash, misconfigured cache settings or an issue with backend applications. Restarting the server, checking database connections and monitoring application logs can help troubleshoot this issue. 

5. Blocked Cloudflare IP addresses 

Some servers inadvertently block Cloudflare IP ranges, restricting access and causing errors in the communication process. This can happen due to security settings, firewall rules or hosting providers mistakenly identifying Cloudflare as a threat.  

How to fix a Cloudflare 520 error 

1. Check server error logs 

1. Log into your hosting control panel or SSH terminal. 
2. Navigate to the error log files (For example, Apache’s error_log or Nginx’s error.log). 
3. Look for entries related to connection resets, unexpected responses or timeouts. 
4. Identify any application crashes or missing resources like files, scripts, or configuration elements the server expects but cannot locate. 
5. Take corrective actions such as restarting services or updating software. 

Also read: How to Access Cpanel Error Logs for Troubleshooting 

2. Review DNS settings 

1. Open your Cloudflare dashboard and go to the DNS settings. 
2. Verify that the A record and CNAME record match the details provided by your hosting provider. 
3. Ensure the proxy status is correctly set (Orange Cloud for Cloudflare protection, Gray Cloud for direct traffic). 
4. Check if the TTL (Time-To-Live) values are correctly set for better resolution speed. 

Also read: What is DNS (Domain Name System) and How Does it Work? 

3. Whitelist Cloudflare IP ranges 

1. Log into your server’s firewall or security settings. 
2. Add Cloudflare’s IP ranges to your firewall whitelist to prevent accidental blocking. 
3. Update security plugins (such as mod_security) to ensure they do not restrict Cloudflare’s traffic. 

4. Examine and adjust response headers 

1. Use browser developer tools (Network tab) or tools like curl -I to inspect response headers. 
2. Remove any unnecessary, malformed or excessively large headers. 
3. Ensure the headers conform to standard HTTP specifications to avoid conflicts. 

5. Restart web services 

1. If using Apache, restart it with sudo systemctl restart apache2. 
2. If using Nginx, restart it with sudo systemctl restart nginx. 
3. If on a shared hosting plan, restart services via the hosting panel. 
4. Check if restarting resolves the issue and monitor server logs for errors. 

6. Disable .htaccess temporarily 

1. Connect to your server using FTP or SSH. 
2. Locate the .htaccess file in the root directory. 
3. Rename it to .htaccess_backup. 
4. Check if the site loads properly after this change. 
5. If the issue is resolved, review .htaccess rules for misconfigurations before restoring. 

7. Pause Cloudflare 

1. Log into your Cloudflare dashboard. 
2. Under Overview, select Pause Cloudflare on Site. 
3. Access the website directly via its IP address to check if the origin server is responding correctly. 
4. If the error persists, troubleshoot the issue on the hosting provider’s side. 

Also read: A detailed guide on using Cloudflare 

Tired of dealing with server-side issues like 520 errors? With Bluehost’s managed hosting you’ll never have to troubleshoot errors again—we handle it for you. 

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Preventing future Cloudflare 520 errors 

1. Regular server maintenance 

Perform routine server maintenance to keep your website running smoothly. This includes: 

• Updating software: Regularly update your web server, CMS, plugins and other applications to ensure security and compatibility. 
• Firewall checks: Ensure your firewall settings are correctly configured to allow legitimate traffic while blocking potential threats. 
• Resource monitoring: Track CPU, memory and disk usage to prevent server overloads and unexpected crashes. 
• Database optimization: Periodically clean up unused data and optimize database queries to improve performance. 

2. Monitor server performance and logs 

Regularly reviewing performance metrics helps detect potential issues before they escalate into 520 errors. Follow these instructions to stay in the clear: 

• Enable logging: Ensure that your web server’s error logs and access logs are enabled. 
• Analyze logs regularly: Check for repeated errors, slow response times and failed requests. 
• Use monitoring tools: Tools like New Relic, Datadog or server-native monitoring solutions can help provide real-time insights. 
• Set up alerts: Configure alerts for unusual traffic spikes, excessive error rates or server downtime so that you can act quickly whenever issues arise. 

3. Configure appropriate timeout settings 

Adjust your server timeout settings to prevent connection interruptions that might cause Cloudflare to return a 520 error: 

• Increase timeout values: Set higher timeout limits for PHP, Apache or Nginx to accommodate slow responses. 
• Optimize application response time: Identify slow database queries or inefficient code that might delay responses. 
• Configure keep-alive settings: Ensure that persistent connections are allowed to improve data transfer efficiency. 
• Test with different settings: Gradually adjust timeout settings and monitor the impact on the performance to find an optimal balance. 

Final thoughts 

A Cloudflare 520 error may seem like a frustrating roadblock, but with the right troubleshooting approach, it’s a problem you can solve. By identifying the root causes, tweaking server settings and implementing proactive measures, you can keep your website stable, accessible and error-free. 

Preventing future errors isn’t just about quick fixes, it’s about building a reliable foundation for your site. If you’d rather prefer a more hands-off approach, we can ensure 100% uptime and dedicated support with our hosting. 

Contact Bluehost today to know more about our managed hosting service. 

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