Idempotency — Making Operations Safe to Retry
Design idempotent APIs with idempotency keys, handle at-least-once delivery safely, and implement deduplication across distributed systems.
A user clicks "Place Order." The request times out. Did the order go through? The user clicks again. Now there are two orders and two credit card charges.
This is the idempotency problem, and it shows up everywhere in distributed systems. Networks are unreliable. Requests get lost. Responses get lost. Clients retry. Message queues deliver duplicates. Without idempotent operations, every retry risks unintended side effects.
Idempotency means that performing the same operation multiple times produces the same result as performing it once. It is the foundation of reliable distributed systems.
What Idempotency Means
An operation is idempotent if calling it once or calling it N times produces the same result.
Idempotent:
SET user.name = "Alice"
SET user.name = "Alice" ← This lesson is part of the Guild Member curriculum. Plans start at $29/mo.