Idempotency in Distributed Calls
Guarantee safe retries over unreliable networks: Idempotency keys, unique database constraints, conditional writes, and deduplication caches.
01.1. What is Idempotency and Why is it Mandatory in Distributed Systems?
In mathematics and computer science, an operation is idempotent if applying it multiple times produces the exact same end state as applying it once:
f(f(x)) = f(x)
The Network Timeout Dilemma:
In distributed systems, networks are inherently unreliable. When an API client calls POST /payments/charge and encounters a 5-second network timeout, the client has no way of knowing whether:
- The request timed out before reaching the server (card was not charged).
- The server successfully charged the customer's card, but the HTTP
200 OKresponse was dropped on the return route (card was charged).
If the client retries blindly without idempotency protection, the customer will be charged twice. If the client does not retry, the order may fail silently.
Idempotency makes network retries 100% safe.
Idempotent API Request Lifecycle 🔑
Idempotent API Request Lifecycle 🔑
Preventing duplicate payment execution using Idempotency-Key headers.
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