Why REST API design for systems in HLD? - Purpose & Use Cases

The Big Idea

What if your systems could talk to each other as easily as sending a text message?

The Scenario

Imagine you have multiple software systems that need to talk to each other. Without a clear way to communicate, each system uses its own method, like sending emails or calling each other on the phone. This makes sharing data slow and confusing.

The Problem

Using manual methods to connect systems is slow and full of mistakes. Each system might expect different formats or messages, causing errors. It's like trying to understand someone speaking a different language without a translator.

The Solution

REST API design creates a simple, common language for systems to talk. It uses clear rules and standard formats so every system understands each other easily. This makes communication fast, reliable, and easy to maintain.

Before vs After

✗ Before

Send email with data
Wait for reply
Parse reply manually

✓ After

GET /users/123 HTTP/1.1
Host: api.example.com
Accept: application/json

What It Enables

With REST API design, systems can connect smoothly and scale easily, unlocking powerful integrations and automation.

Real Life Example

Online shopping sites use REST APIs to connect their inventory, payment, and shipping systems so your order is processed quickly and correctly.

Key Takeaways

Manual system communication is slow and error-prone.

REST APIs provide a clear, standard way for systems to interact.

This leads to faster, more reliable, and scalable system integration.

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