Idempotent API Explained

Ensure safe retries without duplicate side effects — the API design principle that prevents double charges, duplicate orders, and data corruption.

Idempotent API

An idempotent API endpoint produces the same result regardless of how many times the same request is sent, ensuring safe retries without causing duplicate side effects like double charges or duplicate records.

Explanation

Network failures, timeouts, and retries are inevitable in distributed systems. Without idempotency, retrying a failed payment request might charge the customer twice. Idempotent APIs guarantee that repeating the same request produces the same outcome. Implementation typically uses idempotency keys: the client sends a unique key with each request, and the server stores the result. If the same key is sent again, the server returns the stored result instead of re-executing the operation. HTTP methods GET, PUT, and DELETE are inherently idempotent; POST is not and requires explicit implementation.

Bookuvai Implementation

Bookuvai implements idempotency for all state-changing API endpoints, especially payment and order processing. We use idempotency keys stored in Redis with configurable TTLs, return cached responses for duplicate requests, and ensure database operations use upsert patterns where possible.

Key Facts

  • Same request produces same result regardless of repetition count
  • Essential for safe retries in distributed systems
  • Idempotency keys let servers detect and deduplicate repeated requests
  • GET, PUT, DELETE are naturally idempotent; POST requires explicit implementation
  • Critical for payment processing, order creation, and financial operations

Related Terms

Frequently Asked Questions

How do idempotency keys work?
The client generates a unique key (UUID) and sends it with the request. The server checks if that key was seen before. If yes, it returns the stored result. If no, it processes the request and stores the result keyed by the idempotency key.
How long should idempotency keys be stored?
Store keys long enough to cover retry windows — typically 24-48 hours. Shorter TTLs risk missing retries after extended outages. Longer TTLs consume more storage. For payment operations, err on the side of longer retention.
Are all REST methods idempotent?
GET, PUT, DELETE, and HEAD are idempotent by definition. POST and PATCH are not inherently idempotent. POST creates new resources (repeating creates duplicates), so POST endpoints need explicit idempotency implementation.