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HTTP_STATUS_REQUEST_HEADER_TOO_LARGE
The code is not standardized. Oversized cookies, long authorization tokens, many forwarding headers, or generated tracing headers are common causes. Other servers may return 400 or 431 for the same underlying condition.
Measure the complete request header size and review NGINX header-buffer settings together with application cookie policy. Raising limits should be deliberate because it increases per-connection memory use.
Because 494 is internal to NGINX rather than standardized HTTP, clients should not depend on seeing it as an ordinary response code. Investigate the configured request-header limits and actual incoming headers, especially large Cookie fields. Raising buffer limits without controlling unbounded header growth can merely postpone the same failure.
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