ARCHITECTURE Signal 165
The First Idempotency Key
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Engineers rely on idempotency keys daily to handle the fundamental distributed systems problem that exactly-once delivery is impossible and instead guarantee exactly-once processing through de-duplication. Understanding the pattern's history clarifies that Stripe named but did not invent the concept, and earlier implementations like Amazon EC2's ClientToken and Nottingham's POE draft predate it.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
Idempotency keys solve the core distributed systems problem that exactly-once delivery is impossible by enabling exactly-once processing through message de-duplication.
Stripe popularized the "Idempotency-Key" header around 2015, but the pattern predates it—Amazon EC2's ClientToken and Mark Nottingham's 2005 "POST Once Exactly" draft are earlier documented instances.
The current IETF draft specification for idempotency keys credits both Stripe's documented patterns and Nottingham's 2005 draft as origins.
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