HTTP troubleshooting
520 Web Server Returned an Unknown Error
Your uptime monitor detected that the request reached the edge proxy network, but the origin web server returned an empty, unknown, or unexpected response that the proxy could not understand.
What 520 Status Code Means
- 1.
Protocol mismatches
The origin server sent back data that broke standard HTTP communication rules, making it unreadable.
- 2.
Connection drops
The backend server abruptly terminated the connection while the proxy was waiting for a full header response.
- 3.
Excessive header sizes
The origin web server sent back a response header payload that was too large for the cloud proxy to process.
Troubleshooting checklist
- 1.
Inspect origin error logs
Look directly into your NGINX or Apache error logs at the time of the crash to find dropped connection markers.
- 2.
Review custom headers
Check if your backend application is outputting broken, malformed, or excessively long custom cookie data.
- 3.
Examine server response states
Verify if specific scripts are crashing quietly right before they finish compiling their response data.
- 4.
Monitor system memory limits
Check if the server is running out of memory mid-transaction, causing it to clip the response payload short.
How to Fix It
- 1.
Fix malformed output scripts
Correct any backend code execution bugs that output raw text data before sending proper HTTP headers.
- 2.
Increase proxy buffer limits
Configure your web server settings to expand allowable header and buffer size capacities for clean processing.
- 3.
Restart web server daemons
Reboot your core web services to clear out corrupted worker loops that might be mangling response strings.
- 4.
Adjust security proxy filters
Tune down over-sensitive backend security modules that mangle incoming headers from proxy networks.
After the Service is Fixed
- 1.
Verify with Uptime Monitor
Confirm that the monitoring console logs a clean 200 OK once the origin server formats its output correctly.
- 2.
Track script memory bounds
Monitor application execution profiles to catch scripts that approach resource exhaustion ceilings.
- 3.
Validate header string integrity
Use diagnostic tools to check the exact layout of headers sent by your application for standards compliance.
- 4.
Review application updates
Audit recent code deployments to identify components that might have introduced unstable response formatting.