REST API design for systems in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding REST API Statelessness

Which statement best describes the statelessness principle in REST API design?

A API requests can depend on previous requests to complete successfully.

B The server must store session information to track user state between requests.

C Each API request must contain all information needed to process it, without relying on stored context on the server.

D Clients should maintain no state and rely on the server to remember previous interactions.

💡 Hint

Think about how REST APIs handle client-server communication without storing session data.

REST APIs are stateless, meaning each request is independent and contains all necessary information. The server does not store client context between requests.

❓ Architecture

intermediate

Choosing HTTP Methods for REST API

Which HTTP method is the most appropriate for updating an existing resource completely in a REST API?

A PUT

B POST

C GET

D DELETE

💡 Hint

Consider which method replaces the entire resource at the given URI.

PUT is used to update or replace an existing resource completely. POST is usually for creating new resources, GET for retrieving, and DELETE for removing.

❓ scaling

advanced

Scaling REST APIs with Caching

Which caching strategy best improves REST API scalability by reducing server load for frequently requested data?

A Disable caching to always serve fresh data.

B Use client-side caching with cache-control headers and ETags.

C Store all responses permanently on the server without expiration.

D Cache only POST request responses on the client.

💡 Hint

Think about how HTTP headers help clients avoid unnecessary requests.

Client-side caching with cache-control headers and ETags allows clients to reuse responses when data hasn't changed, reducing server load and improving scalability.

❓ tradeoff

advanced

Tradeoffs in REST API Versioning

What is a common tradeoff when using URI versioning (e.g., /v1/resource) in REST API design?

A It eliminates the need for documentation since versions are clear in the URI.

B It allows seamless backward compatibility without any extra server maintenance.

C It forces clients to always use the latest API version without choice.

D It simplifies client requests but can lead to duplicated code and maintenance overhead on the server.

💡 Hint

Consider how versioning affects server code and client flexibility.

URI versioning makes it clear which API version is used but can cause duplicated endpoints and extra maintenance effort on the server side.

❓ estimation

expert

Estimating API Throughput for a High-Traffic REST Service

A REST API server handles 10,000 requests per second on average. Each request takes 50ms of server processing time. How many concurrent requests must the server handle to sustain this throughput without queuing?

A 500 concurrent requests

B 200 concurrent requests

C 50 concurrent requests

D 1000 concurrent requests

💡 Hint

Use Little's Law: Concurrent = Throughput × Latency.

Little's Law states that the number of concurrent requests equals throughput multiplied by average processing time. 10,000 req/s × 0.05 s = 500 concurrent requests.

Practice

1. Which HTTP method is typically used to retrieve data from a REST API without modifying it?

easy

A. DELETE

B. POST

C. GET

D. PUT

Solution

1. Step 1: Understand HTTP methods in REST

   GET is used to request data without changing the server state.

2. Step 2: Match method to action

   POST creates or modifies data, PUT updates, DELETE removes data.

3. Final Answer:

   GET -> Option C

4. Quick Check:

   Retrieve data = GET [OK]

Hint: GET is for reading data only, no changes [OK]

Common Mistakes:

• Confusing POST with GET
• Using PUT for data retrieval
• Thinking DELETE retrieves data

2. Which of the following is the correct URL format to access a specific user with ID 123 in a REST API?

easy

A. /users/123

B. /users/getUser?id=123

C. /getUser/123

D. /users?id=123

Solution

1. Step 1: Identify RESTful URL design

   REST URLs use resource names and IDs as path segments, not actions or query for specific resource.

2. Step 2: Compare options

   /users/123 correctly points to user resource with ID 123; others use verbs or query parameters incorrectly.

3. Final Answer:

   /users/123 -> Option A

4. Quick Check:

   Resource ID in path = /users/123 [OK]

Hint: Use resource path + ID, avoid verbs in URL [OK]

Common Mistakes:

• Using verbs like getUser in URL
• Using query params for resource ID
• Mixing action names with resource paths

3. Given the following REST API call: DELETE /orders/456, what is the expected outcome?

medium

A. It deletes order 456 from the system

B. It updates order 456's status

C. It retrieves order 456's details

D. It creates a new order with ID 456

Solution

1. Step 1: Understand HTTP DELETE method

   DELETE is used to remove a resource identified by the URL.

2. Step 2: Analyze the URL and method

   /orders/456 points to order with ID 456; DELETE removes it.

3. Final Answer:

   It deletes order 456 from the system -> Option A

4. Quick Check:

   DELETE + resource ID = delete resource [OK]

Hint: DELETE method removes resource at given URL [OK]

Common Mistakes:

• Thinking DELETE retrieves data
• Confusing DELETE with POST
• Assuming DELETE creates or updates

4. A developer designed a REST API endpoint as POST /users/123/updateEmail to update a user's email. What is the main issue with this design?

medium

A. Using POST instead of GET for update

B. Including action 'updateEmail' in the URL violates REST principles

C. Missing user ID in the URL

D. Using query parameters instead of path variables

Solution

1. Step 1: Review REST URL design principles

   REST APIs should use resource paths, not actions in URLs.

2. Step 2: Identify the problem in the URL

   Including 'updateEmail' is an action, which breaks REST design; updates should use PUT or PATCH on /users/123.

3. Final Answer:

   Including action 'updateEmail' in the URL violates REST principles -> Option B

4. Quick Check:

   URLs represent resources, not actions [OK]

Hint: Avoid verbs in URLs; use HTTP methods for actions [OK]

Common Mistakes:

• Using verbs in URL paths
• Confusing POST with GET for updates
• Omitting resource IDs

5. You need to design a REST API for a system managing books and their authors. Which design best follows REST principles for retrieving all books by a specific author with ID 789?

hard

A. /books/authors/789

B. /books?author=789

C. /getBooksByAuthor/789

D. /authors/789/books

Solution

1. Step 1: Understand resource hierarchy in REST

   Authors and books are resources; books by an author are a sub-resource of author.

2. Step 2: Evaluate URL options

   /authors/789/books clearly shows books belonging to author 789, following REST resource nesting.

3. Step 3: Consider query vs path

   While query parameters can filter, nested resource path is more RESTful for related resources.

4. Final Answer:

   /authors/789/books -> Option D

5. Quick Check:

   Nested resource path shows relationship [OK]

Hint: Use nested paths for related resources [OK]

Common Mistakes:

• Using verbs in URL
• Overusing query parameters
• Ignoring resource relationships