What is idempotency and why is it important in API design?

[fastqa]

Idempotency is a property of certain operations in which the result of performing the operation multiple times is the same as the result of performing it once.

Importance in API Design

• Consistency: Ensures that repeated requests do not lead to inconsistent results or unintended side effects.
• Reliability: Helps in handling network issues where a client might retry requests, ensuring the same outcome.
• Safety: Prevents duplicate transactions, which is crucial in financial applications.

Example

Consider an API endpoint for creating a user:

POST /users

If this endpoint is idempotent, multiple identical requests will create only one user, avoiding duplicates.

Common Pitfalls

• Non-idempotent Operations: Operations like POST can be non-idempotent if not designed carefully.
• State Management: Ensuring idempotency might require managing state or using unique identifiers.

Use Cases

• Payment Processing: Ensuring a payment is processed only once.
• Resource Creation: Avoiding multiple identical resources being created.