Fundamentals of Designing Idempotent REST APIs Quiz

Explore key principles and best practices for designing idempotent REST APIs, including idempotent methods, safe data changes, and practical scenarios. This quiz helps you identify common mistakes and solidify your understanding of reliable API operations and request handling.

1. Definition of Idempotence

   Which statement best defines idempotence in the context of REST APIs?

   1. Sending the same request once or multiple times achieves the same result.
   2. Each request always creates a new resource.
   3. Only GET requests are allowed multiple times.
   4. Requests only succeed on the first try.

   Explanation: Idempotence means that repeating the same request will not further change the system beyond the first application, ensuring consistency. Option B is incorrect because creating a new resource each time is not idempotent. Option C mistakenly suggests requests only work once, which is false. Option D wrongly limits idempotence to GET methods, while it applies to several HTTP methods.

2. Idempotent HTTP Methods

   Which of the following HTTP methods is inherently idempotent according to REST standards?

   1. PATCH
   2. CONNECT
   3. PUT
   4. POST

   Explanation: PUT is idempotent as sending the same request multiple times results in the same resource state. POST is not idempotent since it typically creates new resources. CONNECT is used to establish a tunnel and is not considered idempotent. PATCH is generally not idempotent, as it partially modifies resources.

3. Example of Idempotent Operation

   Given a REST API to update a user's email, which implementation describes an idempotent operation?

   1. A POST request that adds a user to the database every time.
   2. A PATCH request that increments the user's age by one.
   3. A GET request returning a list of users with random order.
   4. A PUT request that always updates the user email to user@example.com.

   Explanation: A PUT request that sets a fixed value is idempotent, as repeated requests have the same effect. The POST request creates duplicates, violating idempotence. Incrementing with PATCH is not idempotent because repeated requests further increment the value. A randomized GET response doesn’t affect server state and randomness is irrelevant to idempotence in this context.

4. Importance of Idempotency

   Why is designing idempotent endpoints important for REST APIs, especially with network retry scenarios?

   1. It allows all HTTP requests to change data.
   2. It limits access to sensitive data.
   3. It improves user interface rendering only.
   4. It prevents repeated requests from causing unintended side effects.

   Explanation: Idempotency ensures repeated requests do not cause duplicate or harmful changes, which is crucial when network issues cause retries. Option B is misleading, as idempotency restricts, not expands, data-changing potential. Option C incorrectly associates idempotency with UI rendering. Option D relates to security, not idempotence.

5. Distinguishing Safe and Idempotent Methods

   Which HTTP method is both safe and idempotent according to REST standards?

   1. POST
   2. PATCH
   3. DELETE
   4. GET

   Explanation: GET is both safe (does not modify resources) and idempotent (repeated calls return the same data). DELETE is idempotent but not safe since it removes data. POST can modify data and is not idempotent. PATCH is neither safe nor always idempotent.

6. Idempotency in DELETE Operations

   What makes a properly implemented DELETE operation idempotent in a REST API?

   1. Every DELETE request creates a new resource.
   2. Deleting the same resource repeatedly results in the same outcome after the first deletion.
   3. Each request to DELETE increments a resource version number.
   4. DELETE always fails on the second request.

   Explanation: A DELETE request is idempotent because deleting a missing or already deleted resource still results in the same system state. Option B is incorrect as DELETE should not create resources. Option C is wrong since a well-designed API will simply report the absence. Option D means repeated requests change state, violating idempotency.

7. Making POST Requests Idempotent

   Which practice can help make POST requests idempotent in a REST API?

   1. Allowing duplicate resource creation.
   2. Including a unique idempotency key in the request header.
   3. Randomizing response codes on repeated requests.
   4. Using GET instead of POST for data creation.

   Explanation: An idempotency key ensures the server recognizes repeated POSTs as the same request and avoids duplicate results. Option B would defeat the purpose of idempotency. GET is not suitable for resource creation and is not a replacement for POST. Option D adds unpredictability and does not address duplicate prevention.

8. Idempotency vs. Concurrency

   If multiple clients send identical PUT requests to update a user's phone number at the same time, what does idempotency guarantee?

   1. The phone number will be different after each update.
   2. The server rejects all requests except one.
   3. Only the first request updates the phone number.
   4. The resource will end up with the specified phone number regardless of how many requests are sent.

   Explanation: With idempotent PUT requests, the end result remains consistent regardless of the number of repetitions. Option B confuses idempotency with single-use operations. Option C contradicts the core principle that repeated PUTs yield the same result. Option D misleadingly suggests server rejection rather than consistent application.

9. Detecting Non-Idempotent Operations

   Which example describes a non-idempotent REST API operation?

   1. A PUT endpoint that updates a user's profile picture to the same image.
   2. A POST endpoint that creates a new order with each request.
   3. A DELETE endpoint that removes a specific comment.
   4. A GET endpoint that retrieves product details by ID.

   Explanation: POST typically creates resources and repeated requests can create multiple orders, violating idempotence. The PUT request causes no further change after the image is set. DELETE is idempotent since removing a removed comment doesn't cause more change. GET does not modify resources, maintaining safety and idempotency.

10. Handling Failures for Idempotency

    When implementing an idempotent endpoint, how should the server handle a repeated client request after a failure, such as a timeout?

    1. Process the request as if it were the same as the first attempt and ensure resource state does not change further.
    2. Deny the request and report an error to the client.
    3. Restart the entire transaction history for that resource.
    4. Always return a different resource state after each retry.

    Explanation: An idempotent endpoint ensures repeated identical requests lead to the same outcome and do not cause extra changes. Returning a different resource state on retries would violate idempotency. Denying retries offers no reliability benefit. Replaying all previous transactions is unnecessary overhead and not required for idempotent design.