Fix Nginx 502 Bad Gateway: Upstream Connection Refused - Troubleshooting Cloudflare 521 Connection Error-Docker Nginx 502 Bad Gateway After Restart Fix

Updated 2026-07-28 02:37:00office-tools
Fix Nginx 502 Bad Gateway: Upstream Connection Refused - Troubleshooting Cloudflare 521 Connection Error-Docker Nginx 502 Bad Gateway After Restart Fix
Before changing system settings, save your work and note the exact error text so you can compare results after each step.

Extra verification checklist

  • Restart the affected app after changing permissions or configuration files.
  • Test the same workflow in a clean browser profile or a temporary user account.
  • Compare the result on another network if the error may be connection related.