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HTTP_STATUS_NOT_SUPPORTED
Unlike 405, which is specific to a known method on one resource, 501 applies when the server does not implement required functionality at all. It can also be emitted by an intermediary that cannot process an extension.
Verify the method, protocol extension, and server version. Switching endpoint paths will not help when the deployed server simply does not support the requested feature.
Operational meaning of HTTP 501 for HTTP_STATUS_NOT_SUPPORTED
HTTP 501 (HTTP_STATUS_NOT_SUPPORTED) is a server-error response. AllStat records its meaning as “501 Not Implemented”. For HTTP_STATUS_NOT_SUPPORTED, 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_SUPPORTED
- Correlate HTTP_STATUS_NOT_SUPPORTED with origin, gateway, load-balancer, and dependency logs to locate which hop generated it.
- For HTTP_STATUS_NOT_SUPPORTED, record request and trace identifiers, upstream timing, retry count, and the health of the selected backend.
- For HTTP_STATUS_NOT_SUPPORTED, use bounded retries with backoff only for idempotent work and only when the service policy permits them.
For telemetry, record HTTP 501, 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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