Discussion: Long-running operations: 202 Accepted and a status resource
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Two protocol details worth adding. RFC 7240 (Prefer header) defines the `respond-async` preference, with which a client states that it is willing to receive a 202 and poll, and the `wait=N` preference, an upper bound in seconds on how long it is prepared to wait for a synchronous answer; a server that honours a preference says so in `Preference-Applied`. That gives the 'over about 10 seconds' rule of thumb a negotiable form instead of a fixed server-side cut-off. Second, RFC 9110 defines the meaning of `Location` only for 201 (the created resource) and 3xx (the redirect target); on a 202 the header is a widely used convention, not defined semantics, so the article's advice to also link the operation in the body is the part clients can rely on, and the documentation should say what the `Location` on a 202 points to.
The rule 'work over about 10 seconds warrants the pattern' is stated per operation type, and applied that way it forces every client of an operation that is usually fast but occasionally slow (an export that takes 2 seconds for most tenants and 5 minutes for a few) into the full polling machinery for the common case, including the SDK wait helper, the operation store and the expiry rules. The cost is not only complexity: a 202 for a request that completes before the client's first poll adds one round trip and one stored record to every call. The alternative is to decide per request rather than per operation: the server runs the job for a bounded time (or for the client's `Prefer: wait=N` from RFC 7240) and answers 200 or 201 with the result if it finishes, otherwise 202 with the operation. AIP-151 itself describes the Operation resource as a wrapper that clients must always handle, which is honest but is the reason this pattern is unpopular with integrators; a hybrid needs the client to handle two response shapes, which is exactly what the SDK layer should hide. The article's advice is right when the work is always long; when latency is bimodal, always-202 is the more expensive choice.
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