Portfolio ↗

Idempotency Keys

Client-generated keys stored atomically with the operation they guard.

5Questions
7Flashcards
3Terms
Drill this topic All of API & Integration Architecture
Questions

5 to work through

  1. advanced

    A card-issuing platform exposes an API where duplicate requests would move money twice. What is the complete idempotency contract, including the cases most implementations miss?

    2 min answer
  2. advanced

    A payment API supports idempotency keys. Duplicate charges still occur occasionally. The server implementation is correct. Where is the bug?

    2 min answer
  3. advanced

    A payment integration retries on timeout. Finance reports occasional double charges. The provider supports idempotency keys and they are being used. Diagnose.

    2 min answer
  4. advanced

    A payments API must guarantee that a network retry never charges a customer twice. Design the mechanism end to end.

    2 min answer
  5. advanced

    A payments flow in a mobility app creates duplicate charges when the mobile network drops the response and the client retries. Design the idempotency mechanism and identify where teams most often get it wrong.

    2 min answer
Terminology

3 terms in this topic

pattern

Idempotency Key

A client-generated identifier that lets a server recognise a retried request and return the original result instead of performing the action twice.

 concept

Idempotency Scope

The boundary within which an idempotency key is unique and meaningful — per account, per endpoint, or global — and the retention window it lives for.

 case-study

Stripe: Idempotency Keys as a Public API Contract

Stripe made safe retry a documented, client-controlled property of its API, which is why network failures during payments do not produce duplicate charges.
API & Integration Architecture

Neighbouring topics

API & Integration

General material on integrating systems through contracts.

4 quiz 15 cards 13 terms

REST Design

Resources, uniform methods, status codes and statelessness.

4 quiz 7 cards 3 terms

GraphQL

Client-specified queries, N+1 resolution and query-cost control.

4 quiz 9 cards 4 terms

gRPC APIs

Contract-first RPC, generated clients and protobuf compatibility rules.

3 quiz 8 cards 3 terms

Webhooks

Push callbacks, signature verification, ordering and at-least-once delivery.

5 quiz 12 cards 7 terms

API Versioning

URL, header and account-pinned versioning, and who carries the burden.

5 quiz 9 cards 5 terms

Backward Compatibility

Which changes are safe, and how to make breakage a build failure.

3 quiz 6 cards 3 terms

Contract Testing

Verifying what consumers actually rely on, without a shared environment.

5 quiz 12 cards 2 terms

API Documentation

OpenAPI as a machine-checked contract rather than as prose.

4 quiz 5 cards 2 terms

Rate Limiting

Algorithms, shared counters, and signalling rejection properly.

4 quiz 12 cards 4 terms

Pagination & Filtering

Offset versus cursor, stable ordering and unbounded result sets.

4 quiz 7 cards 3 terms

API Error Handling

Error shapes, retryability signals and machine-readable causes.

3 quiz 11 cards 4 terms

Event-Driven Integration

Publishing facts rather than commands, and versioning event schemas.

4 quiz 11 cards 5 terms

Message Formats

JSON, Protobuf, Avro — schema evolution and payload economics.

3 quiz 8 cards 2 terms

Schema Registry

Enforcing compatibility on events the way CI enforces it on code.

2 quiz 7 cards 4 terms

Integration Patterns

Routers, translators, splitters, aggregators and dead letter channels.

3 quiz 8 cards 6 terms

Legacy Integration

Reaching systems that cannot change, without importing their model.

4 quiz 11 cards 3 terms

Partner & B2B Integration

External contracts, onboarding, sandboxes and long deprecation windows.

4 quiz 9 cards 3 terms

APIs as Products

Ownership, lifecycle, deprecation policy and developer experience.

5 quiz 12 cards 3 terms