REST API between services in Microservices - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main advantage of using REST APIs between microservices?

Consider a system where multiple microservices communicate using REST APIs. What is the primary benefit of this approach?

A It enforces a strict contract and allows services to evolve independently.

B It requires all services to be written in the same programming language.

C It eliminates the need for any authentication or security measures.

D It guarantees zero network latency between services.

💡 Hint

Think about how REST APIs help services stay loosely connected.

REST APIs define clear contracts through endpoints and data formats, allowing each service to change internally without affecting others, promoting independent evolution.

❓ Architecture

intermediate

Which component is essential to manage REST API calls between microservices for load balancing?

In a microservices architecture using REST APIs, which component helps distribute incoming requests evenly across service instances?

A Message Queue

B Database Proxy

C API Gateway

D Load Balancer

💡 Hint

Think about what balances traffic among multiple servers.

A Load Balancer distributes incoming REST API requests across multiple instances of a service to ensure no single instance is overwhelmed.

❓ scaling

advanced

What is the best approach to handle high traffic REST API calls between microservices to avoid bottlenecks?

You notice that a microservice is overwhelmed by REST API calls from other services during peak times. Which approach best helps to scale and avoid bottlenecks?

A Disable caching to ensure fresh data on every request.

B Increase the timeout value for REST API calls to wait longer for responses.

C Implement asynchronous communication using message queues instead of direct REST calls.

D Reduce the number of service instances to limit traffic.

💡 Hint

Think about decoupling services to handle load better.

Using asynchronous messaging reduces direct REST API call load, allowing services to process requests at their own pace and improving scalability.

❓ tradeoff

advanced

What is a tradeoff when using REST APIs synchronously between microservices?

Using synchronous REST API calls between microservices has benefits and drawbacks. Which option correctly describes a tradeoff?

A Synchronous calls simplify error handling but increase latency and reduce fault tolerance.

B Synchronous calls eliminate network overhead but require complex message brokers.

C Synchronous calls guarantee zero data loss but prevent service scaling.

D Synchronous calls allow services to run offline without connectivity.

💡 Hint

Consider how waiting for responses affects system behavior.

Synchronous REST calls make it easier to handle errors immediately but can cause delays and cascading failures if a service is slow or down.

❓ estimation

expert

Estimate the number of REST API requests per second a microservice cluster can handle given these parameters

A microservice cluster has 5 instances. Each instance can handle 200 REST API requests per second. The load balancer distributes requests evenly. What is the total maximum requests per second the cluster can handle?

A 200 requests per second

B 1000 requests per second

C 400 requests per second

D 2500 requests per second

💡 Hint

Multiply the number of instances by the capacity per instance.

5 instances × 200 requests/second each = 1000 requests/second total capacity.

Practice

1. What is the main purpose of using a REST API between microservices?

easy

A. To allow services to communicate over HTTP using standard methods

B. To store data permanently in a database

C. To run services on the same machine only

D. To replace all backend logic with frontend code

Solution

1. Step 1: Understand REST API role in microservices

   REST APIs enable communication between independent services using HTTP methods like GET, POST, PUT, DELETE.

2. Step 2: Identify the correct purpose

   Storing data or running services on the same machine are not the main goals of REST APIs; they focus on communication.

3. Final Answer:

   To allow services to communicate over HTTP using standard methods -> Option A

4. Quick Check:

   REST API = communication over HTTP [OK]

Hint: REST APIs connect services via HTTP methods [OK]

Common Mistakes:

• Confusing REST API with database storage
• Thinking REST APIs run services locally only
• Assuming REST replaces backend logic

2. Which HTTP method is typically used to update an existing resource in a REST API between microservices?

easy

A. GET

B. PUT

C. POST

D. DELETE

Solution

1. Step 1: Recall HTTP methods and their purposes

   GET retrieves data, POST creates new data, PUT updates existing data, DELETE removes data.

2. Step 2: Match method to update action

   Updating a resource is done with PUT, which replaces or modifies the resource at the given URL.

3. Final Answer:

   PUT -> Option B

4. Quick Check:

   Update = PUT [OK]

Hint: PUT method updates resources in REST APIs [OK]

Common Mistakes:

• Using GET to update data
• Confusing POST with update instead of create
• Using DELETE to update resources

3. Consider this REST API call between two services:

GET /users/123

What is the expected result of this request?

medium

A. Retrieve details of the user with ID 123

B. Create a new user with ID 123

C. Delete the user with ID 123

D. Update the user with ID 123

Solution

1. Step 1: Analyze the HTTP method and URL

   The method is GET, which is used to retrieve data. The URL targets user with ID 123.

2. Step 2: Determine the action based on method

   GET requests fetch data without changing it, so it retrieves user details.

3. Final Answer:

   Retrieve details of the user with ID 123 -> Option A

4. Quick Check:

   GET /users/123 = retrieve user data [OK]

Hint: GET fetches data, not modifies it [OK]

Common Mistakes:

• Thinking GET creates or deletes data
• Confusing URL path with action
• Assuming GET updates resources

4. A microservice sends a POST request to another service's REST API but receives a 405 Method Not Allowed error. What is the most likely cause?

medium

A. The request body is missing required fields

B. The URL endpoint does not exist

C. The HTTP method POST is not supported by the endpoint

D. The server is down

Solution

1. Step 1: Understand 405 Method Not Allowed meaning

   This error means the server recognizes the URL but does not allow the HTTP method used.

2. Step 2: Match error to cause

   If POST is not supported on that endpoint, the server rejects it with 405. Other issues cause different errors.

3. Final Answer:

   The HTTP method POST is not supported by the endpoint -> Option C

4. Quick Check:

   405 error = method not allowed [OK]

Hint: 405 means method not allowed on endpoint [OK]

Common Mistakes:

• Confusing 405 with 404 (not found)
• Assuming missing fields cause 405
• Thinking server down causes 405

5. You design two microservices: Service A calls Service B's REST API to get user data. To improve scalability and reduce latency, which design choice is best?

hard

A. Service A calls Service B synchronously for every user request

B. Service A and B share a database to avoid API calls

C. Service B pushes user data to Service A via REST POST requests

D. Service A caches user data locally and refreshes periodically

Solution

1. Step 1: Evaluate synchronous calls impact

   Calling Service B synchronously for every request adds latency and load, reducing scalability.

2. Step 2: Consider caching benefits

   Caching user data locally in Service A reduces calls to Service B, improving response time and scalability.

3. Step 3: Assess other options

   Service B pushing data is complex and not typical REST usage; sharing a database breaks microservice independence.

4. Final Answer:

   Service A caches user data locally and refreshes periodically -> Option D

5. Quick Check:

   Caching improves scalability and latency [OK]

Hint: Cache data locally to reduce cross-service calls [OK]

Common Mistakes:

• Using synchronous calls for every request
• Sharing databases between microservices
• Expecting REST APIs to push data automatically