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After moving an application to a PaaS platform, intermittent 502 errors occur due to Nginx’s retry behavior, HTTP/1.1 connection reuse, and a mismatch between Ingress and uwsgi protocols, which can be diagnosed through error statistics and packet capture.
The article details a step‑by‑step investigation of intermittent 502 errors when routing client requests through Nginx to a Node.js service, identifies malformed URL characters triggering Node's clientError event as the root cause, and presents code and configuration fixes to prevent the issue.
This article analyzes a recurring Nginx 502 Bad Gateway error triggered by oversized response headers from PHP‑FPM, explores whether fastcgi_buffer_size is the root cause, captures communication data between Nginx and PHP‑FPM, conducts systematic tests with varying buffer sizes, and draws conclusions about header handling and buffer configuration.