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Fix nginx 502 Bad Gateway and 504 Gateway Timeout

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Self-Hosting & Infra intermediate 7 min read $0.01 Updated 2026-10-18

Maps nginx error-log messages to causes and fixes for 502 and 504: connection refused, upstream timed out, premature close, socket permission and SELinux denials, oversized upstream headers, stale DNS and timeout tuning.

nginx is up but your app returns 502 or 504. The error log names the exact failure. Match its wording to the cause: refused connection, timeout, socket permission, oversized header or dead upstream.

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#nginx#502#504#reverse-proxy#upstream

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