API gateway patterns in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary role of an API Gateway in microservices architecture?

Choose the best description of the main function of an API Gateway.

A It acts as a single entry point that routes client requests to multiple backend services.

B It directly manages the internal communication between microservices without client involvement.

C It replaces the need for load balancers by distributing traffic evenly.

D It stores all the data for the microservices in a centralized database.

💡 Hint

Think about how clients interact with many services through one interface.

An API Gateway provides a unified entry point for clients, routing requests to appropriate backend services. It does not store data or replace load balancers but complements them.

❓ Architecture

intermediate

Which API Gateway pattern best supports aggregating data from multiple microservices into one response?

Select the API Gateway pattern designed to combine responses from several services into a single client response.

A Aggregator Pattern

B Proxy Pattern

C Chained Pattern

D Facade Pattern

💡 Hint

Think about a pattern that collects and merges data from different sources.

The Aggregator Pattern collects data from multiple backend services and combines it into one response for the client, simplifying client interactions.

❓ scaling

advanced

How does an API Gateway help improve scalability in a microservices system?

Identify the way an API Gateway contributes to system scalability.

A By storing user sessions and state information centrally.

B By caching responses and reducing repeated calls to backend services.

C By directly scaling database clusters automatically.

D By replacing microservices with a monolithic service.

💡 Hint

Consider how reducing backend load can help scale the system.

API Gateways can cache frequent responses, which reduces the number of calls to backend services, thus improving scalability and performance.

❓ tradeoff

advanced

What is a common tradeoff when using an API Gateway in a system architecture?

Choose the main disadvantage or risk introduced by adding an API Gateway.

A It always increases the overall system latency significantly.

B It eliminates the need for security measures in backend services.

C It removes the need for service discovery mechanisms.

D It can become a single point of failure if not designed with redundancy.

💡 Hint

Think about what happens if the gateway stops working.

An API Gateway centralizes traffic, so if it fails and lacks redundancy, it can bring down access to all services, making it a critical point to protect.

❓ estimation

expert

Estimate the number of concurrent connections an API Gateway must handle for a system with 10,000 daily active users, each making 50 requests per hour during peak 2 hours.

Calculate the approximate concurrent connections the API Gateway should support during peak load.

A Approximately 140,000 concurrent connections

B Approximately 14,000 concurrent connections

C Approximately 7,000 concurrent connections

D Approximately 700 concurrent connections

💡 Hint

Calculate total requests during peak, then estimate how many happen simultaneously assuming average request duration.

10,000 users × 50 requests/hour = 500,000 requests/hour. Peak is 2 hours, so 500,000 requests spread over 2 hours = 250,000 requests/hour during peak. That is about 69 requests per second (250,000 / 3600). Assuming each request lasts 100ms (0.1s), concurrent connections = 69 × 0.1 = ~7. So 700 is a safe estimate considering bursts and overhead.

Practice

1. What is the primary role of an API Gateway in a microservices architecture?

easy

A. To act as a single entry point that routes client requests to multiple backend services

B. To store data persistently for backend services

C. To replace all backend services with a monolithic service

D. To serve as a database query optimizer

Solution

1. Step 1: Understand the role of API Gateway

   An API Gateway acts as a single entry point for clients to access multiple backend services, simplifying client communication.

2. Step 2: Eliminate incorrect options

   Options A, C, and D describe roles unrelated to API Gateway functions like data storage or replacing services.

3. Final Answer:

   To act as a single entry point that routes client requests to multiple backend services -> Option A

4. Quick Check:

   API Gateway = Single entry point routing [OK]

Hint: API Gateway = single access point for many services [OK]

Common Mistakes:

• Confusing API Gateway with database or storage
• Thinking API Gateway replaces backend services
• Assuming API Gateway only handles security

2. Which of the following is the correct way to configure an API Gateway to route requests to a backend service named user-service?

easy

A. "/users": "user-service/api/v1/users"

B. "/users": "http://user-service/api/v1/users"

C. "users": "http://user-service/api/v1/users"

D. "/users": "http://user-service/api/v1"

Solution

1. Step 1: Check URL path and protocol

   The route key should start with a slash and the backend URL must include the protocol (http://) and full path.

2. Step 2: Validate each option

   "/users": "http://user-service/api/v1/users" correctly uses "/users" as route and full URL with protocol and path. "/users": "user-service/api/v1/users" misses protocol. "users": "http://user-service/api/v1/users" misses leading slash in route. "/users": "http://user-service/api/v1" misses the full path to users.

3. Final Answer:

   "/users": "http://user-service/api/v1/users" -> Option B

4. Quick Check:

   Route starts with / and URL includes http:// [OK]

Hint: Routes start with / and backend URLs need protocol [OK]

Common Mistakes:

• Omitting http:// in backend URL
• Missing leading slash in route path
• Using incomplete backend service path

3. Given the following API Gateway configuration snippet, what will be the response path for a client request to /orders/123?

{
  "/orders": "http://order-service/api/v2/orders"
}

medium

A. http://order-service/api/v2/orders/orders/123

B. http://order-service/api/v2/orders

C. http://order-service/orders/123

D. http://order-service/api/v2/orders/123

Solution

1. Step 1: Understand path forwarding in API Gateway

   The gateway appends the path after the route key to the backend URL. Here, "/orders" is the route key, so "/123" is appended.

2. Step 2: Construct the full backend URL

   Appending "/123" to "http://order-service/api/v2/orders" results in "http://order-service/api/v2/orders/123".

3. Final Answer:

   http://order-service/api/v2/orders/123 -> Option D

4. Quick Check:

   Request path appended after route key URL [OK]

Hint: API Gateway appends extra path after route key URL [OK]

Common Mistakes:

• Not appending the extra path segment
• Duplicating the route key in backend URL
• Ignoring the original request path

4. An API Gateway is configured with the following routes:

{
  "/products": "http://product-service/api/products",
  "/products/details": "http://product-details-service/api/details"
}

A client request to /products/details/456 returns a 404 error. What is the likely cause?

medium

A. The more specific route "/products/details" is shadowed by the generic "/products" route

B. The backend URL for "/products/details" is missing the protocol

C. API Gateway does not support nested routes

D. The client request path is malformed

Solution

1. Step 1: Analyze route matching order

   API Gateways usually match routes in order or by specificity. If the generic "/products" route is matched first, it will forward requests to product-service, ignoring the more specific route.

2. Step 2: Understand 404 cause

   The product-service likely does not handle "/details/456", causing 404. The specific route is shadowed and never reached.

3. Final Answer:

   The more specific route "/products/details" is shadowed by the generic "/products" route -> Option A

4. Quick Check:

   Route specificity matters to avoid shadowing [OK]

Hint: Specific routes must be checked before generic ones [OK]

Common Mistakes:

• Ignoring route matching priority
• Assuming API Gateway can't handle nested routes
• Blaming client request format without checking routes

5. You need to design an API Gateway pattern that aggregates data from user-service and order-service to provide a single response for a client request to /user-orders/{userId}. Which pattern best fits this requirement?

hard

A. Rate limiting pattern to restrict client requests

B. Simple proxy pattern forwarding requests directly to one service

C. Backend for Frontend (BFF) pattern to combine multiple service responses

D. Circuit breaker pattern to handle service failures

Solution

1. Step 1: Identify the need for data aggregation

   The client wants combined data from two services in one response, which requires aggregation logic.

2. Step 2: Match pattern to requirement

   The Backend for Frontend (BFF) pattern is designed to aggregate and tailor responses for specific client needs by calling multiple backend services.

3. Final Answer:

   Backend for Frontend (BFF) pattern to combine multiple service responses -> Option C

4. Quick Check:

   Data aggregation needs BFF pattern [OK]

Hint: Aggregate multiple services with Backend for Frontend pattern [OK]

Common Mistakes:

• Choosing simple proxy which doesn't aggregate
• Confusing rate limiting with aggregation
• Using circuit breaker which handles failures, not aggregation