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HTTP_STATUS_HEADER_FIELDS_TOO_LARGE
The response can identify the offending header, but it may also be returned for the combined header section. Large cookies, long authorization tokens, forwarding chains, and custom tracing headers are frequent causes.
Capture the request headers and their encoded sizes. Remove stale cookies or reduce oversized headers; changing only the body will not affect a 431 response.
RFC 6585: Additional HTTP Status Codes
Operational meaning of HTTP 431 for HTTP_STATUS_HEADER_FIELDS_TOO_LARGE
HTTP 431 (HTTP_STATUS_HEADER_FIELDS_TOO_LARGE) is a client-error response. AllStat records its meaning as “431 Request Header Fields Too Large”. For HTTP_STATUS_HEADER_FIELDS_TOO_LARGE, interpret it with the request method, selected representation, response headers, and the specification or product that defines the code; the number alone does not prove that application work completed.
Client and server handling for HTTP_STATUS_HEADER_FIELDS_TOO_LARGE
- Treat HTTP_STATUS_HEADER_FIELDS_TOO_LARGE as a condition visible at the request boundary; inspect authentication, syntax, preconditions, routing, and resource state before retrying.
- For HTTP_STATUS_HEADER_FIELDS_TOO_LARGE, preserve the response body and challenge or retry-related headers because they often carry the actionable reason.
- For HTTP_STATUS_HEADER_FIELDS_TOO_LARGE, automatic retry is safe only when the method and status contract allow it and the request has been corrected.
For telemetry, record HTTP 431, method, authority, route template rather than secrets, response headers relevant to caching or retry, latency, upstream identity, and whether the response originated at the application or an intermediary.
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