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HTTP_STATUS_NOT_EXTENDED
It was defined for the experimental HTTP Extension Framework. The response should explain which extension policy or mandatory extension was not satisfied.
Because support is uncommon, verify that the status came from the intended server and inspect its response body. Do not add arbitrary headers unless the application documents the required extension.
RFC 2774: HTTP Extension Framework
Operational meaning of HTTP 510 for HTTP_STATUS_NOT_EXTENDED
HTTP 510 (HTTP_STATUS_NOT_EXTENDED) is a server-error response. AllStat records its meaning as “510 Not Extended”. For HTTP_STATUS_NOT_EXTENDED, 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_NOT_EXTENDED
- Correlate HTTP_STATUS_NOT_EXTENDED with origin, gateway, load-balancer, and dependency logs to locate which hop generated it.
- For HTTP_STATUS_NOT_EXTENDED, record request and trace identifiers, upstream timing, retry count, and the health of the selected backend.
- For HTTP_STATUS_NOT_EXTENDED, use bounded retries with backoff only for idempotent work and only when the service policy permits them.
For telemetry, record HTTP 510, 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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