Nginx Error Reference
1 model · 15 error codes
Browse Nginx error code collections, meanings, and related context across the current corpus.
About Nginx Error Reference
Nginx is a web server, reverse proxy, and load balancer that handles HTTP requests, TLS termination, static file delivery, and upstream proxying. When Nginx operates as a reverse proxy, it sits between the client and a backend application server, forwarding requests and responses. This dual role means Nginx can produce errors from two perspectives: as the server directly responding to the client, and as a proxy reporting upstream failures.
Nginx reports errors through two channels. Standard HTTP status codes (400, 403, 500, 502, 503, 504) appear in both HTTP responses to clients and in access logs. Nginx-specific codes (444, 494, 495, 496, 497, 499) appear only in access and error logs — they are never sent as HTTP response status codes to the client. The 444 code, for example, means Nginx closed the connection without sending any HTTP response at all, which is useful for silently dropping malicious requests. The 499 code means the client disconnected before Nginx finished sending the response.
FixerCode documents 15 Nginx error codes across 1 model, covering both standard HTTP codes that Nginx surfaces and Nginx-specific logging codes. Each entry explains whether the code appears in HTTP responses or only in logs, what triggered it, and how it relates to standard HTTP behavior.
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Frequently Asked Questions
As a web server, Nginx serves static files and terminates TLS directly. As a reverse proxy, Nginx forwards requests to a backend application server (like Node.js, PHP-FPM, or uWSGI) and relays responses back. When acting as a proxy, Nginx can report upstream failures through standard HTTP 5xx codes like 502 (Bad Gateway) and 504 (Gateway Timeout).
Nginx-specific codes like 444 and 499 describe connection-level events that are not part of the HTTP response cycle. A 444 means Nginx closed the connection without sending any response, so there is no HTTP status code to return. A 499 means the client already disconnected, so sending an HTTP response is impossible. These codes exist for logging and diagnostics, not for HTTP communication.
When Nginx acts as a reverse proxy and the backend is slow or unresponsive, Nginx can return a 504 Gateway Timeout to the client. Nginx also logs the upstream response time in its access log, which helps identify which backend requests are consistently slow. The proxy_read_timeout and proxy_connect_timeout directives control how long Nginx waits before reporting a timeout.