Nginx 502/504 Troubleshooting: A Field Engineer's Checklist When your upstream returns 502 or 504, here's the systematic approach I use. The Two Error Codes Code Meaning Typical Cause 502 Bad Gateway Nginx can't reach upstream Upstream down, wrong port, firewall 504 Gateway Timeout Upstream too ...
Source: [Dev.to](https://dev.to/jun_liu_ca219b73a8f1489b5/nginx-502504-troubleshooting-a-field-engineers-checklist-1cge)