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A request whose repeated execution produces the same intended effect as a single execution on the server.
DESCRIPTION
Idempotency ensures that multiple identical requests have the same effect as one, simplifying retries and failure handling. HTTP methods like GET, PUT, and DELETE are defined as idempotent; POST is not. Idempotency is about side effects on server state, not response bodies. Implementing idempotency often involves deduplication keys, conditional requests, or idempotency keys. It is crucial for payment processing, job submission, and distributed systems with at-least-once delivery. Idempotency improves resilience under network retries and client restarts. Logging and auditing should reflect deduplicated operations. Design APIs to clearly document which operations are idempotent and how clients should supply keys.
ALTERNATIVE DEFINITIONS
MDN Web Docs
An HTTP method is idempotent if an identical request can be made once or several times in a row with the same effect while leaving the server in the same state.
Defines idempotency in terms of repeated requests leaving server state unchanged.
IETF RFC
A request method is considered “idempotent” if the intended effect on the server of multiple identical requests with that method is the same as the effect for a single such request.
Normative definition focusing on intended effect on server state.
RELATED TERMS
Safe Methods GET Method PUT Method POST Method Retry Policy Exactly-Once Semantics At-Least-Once Delivery Entity Matching Conditional Requests ETag
COMPETING TERMS
Non-idempotent Request
KNOWLEDGE AREAS
Software Engineering Data Integration & Interoperability Testing & Validation
TARGET AUDIENCE
Software Developer DevOps Engineer MLOps Engineer Cloud Architect
EXTERNAL SOURCES
- Wikipedia - Idempotence
- Stripe - Practical idempotency key guidance
- AWS Builders’ Library - Designing safe retries with idempotency
TOP QUESTIONS
Why are Idempotent Requests important?
They make retries safe, simplifying error handling and improving resilience in unreliable networks and distributed systems.
Category: Relevancy
Which HTTP methods are Idempotent Requests?
GET, PUT, DELETE, HEAD, OPTIONS, and TRACE are idempotent by definition. POST is not idempotent.
Category: Overview
How do idempotency keys work for Idempotent Requests?
Clients send a unique key; servers record the first result and replay it for duplicate requests, preventing duplicate side effects.
Category: How-to
What is a common mistake with Idempotent Requests?
Assuming identical responses; idempotency concerns side effects, not necessarily identical payloads or timestamps.
Category: Misunderstanding
How do conditional requests support Idempotent Requests?
ETags and If-Match ensure updates apply only if the resource matches an expected version, avoiding unintended changes.
Category: Requirements
Can Idempotent Requests depend on business rules?
Yes, idempotency may require domain logic to deduplicate or ignore duplicates, especially in financial systems.
Category: Opinion
How do retries interact with Idempotent Requests?
Retries are safe for idempotent operations; for non-idempotent ones, use keys or transactional outbox patterns.
Category: Requirements
What’s a hot topic around Idempotent Requests?
Standardizing idempotency keys and status semantics for replayed operations is gaining attention across APIs.
Category: Topic
How to test Idempotent Requests?
Invoke the same request multiple times and assert identical state changes. Use chaos tests with injected failures.
Category: Testing