How should an API signal temporary overload, and how should a client combine Retry-After, timeouts, and retries safely?

Retry-After, timeouts, and safe client retries

Coordinates server retry signals with client backoff, deadlines, idempotency, overload protection, and bounded retry budgets.

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TL;DR

A rate-limited request commonly returns 429, while temporary service unavailability can return 503. Either can include Retry-After as a delay in seconds or an HTTP date. The client respects that signal when practical, otherwise uses bounded exponential backoff with jitter. It retries only operations whose semantics make repetition safe, and it stops when the caller's cancellation or overall deadline expires.

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429, 503, Retry-After, exponential backoff, jitter, deadlines, idempotency, retry budgets, circuit breakers, and overload recovery.

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Why this question matters
Retries can recover from brief faults or multiply an outage. The server and client need a shared protocol signal plus a bounded policy for ambiguous outcomes and limited capacity.
A rate-limited request commonly returns 429, while temporary service unavailability can return 503. Either can include Retry-After as a delay in seconds or an HTTP date. The client respects that signal when practical, otherwise uses bounded exponential backoff with jitter. It retries only operations whose semantics make repetition safe, and it stops when the caller's cancellation or overall deadline expires.
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A timeout is ambiguous: the server may have completed the work after the client stopped waiting. GET can normally be retried, but a write needs idempotent method semantics or an idempotency key. I cap attempts, avoid retrying deterministic 4xx failures, and separate connection, per-attempt, and total-operation timeouts. Circuit breaking can stop repeated calls to a failing dependency, but it does not replace the retry budget or a useful fallback. Retry-After should reflect a capacity policy the service can actually honor.

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Retrying every exception and every non-200 response.
Starting a fresh full timeout for every attempt.
Retrying non-idempotent writes without an idempotency design.
Using identical fixed delays across all clients.

How should an API signal temporary overload, and how should a client combine Retry-After, timeouts, and retries safely?

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How should an API signal temporary overload, and how should a client combine Retry-After, timeouts, and retries safely?

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Tech stacks

Skill areas

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