GraphQL vs REST Interview Questions and Answers (15 Must-Know Questions)

Master GraphQL vs REST with 15 interview questions and answers. Learn architecture differences, performance, caching, versioning, security, scalability, Spring Boot implementation, enterprise use cases, migration strategies, and production best practices.

Introduction

REST has been the dominant architectural style for building web APIs for over two decades. It is simple, resource-oriented, cache-friendly, and widely adopted across enterprise systems.

GraphQL, introduced by Facebook (Meta) in 2015, offers a different approach. Instead of exposing multiple REST endpoints with fixed responses, GraphQL provides a single endpoint where clients request exactly the data they need.

Both technologies solve API communication problems, but they excel in different scenarios. REST is ideal for straightforward CRUD services, caching, and public APIs, while GraphQL shines in applications with complex data relationships, multiple client types, and rapidly evolving user interfaces.

Modern enterprises often use both REST and GraphQL together, selecting the right technology for each use case rather than replacing one with the other.

What You'll Learn

REST vs GraphQL
Architecture Differences
Performance
Caching
Versioning
Security
Scalability
Spring Boot Support
Enterprise Use Cases
Migration Strategies

REST vs GraphQL Architecture

               REST Architecture

Client
   │
   ▼
GET /users
GET /orders
GET /payments
   │
   ▼
Spring Boot REST Services
   │
   ▼
Database


--------------------------------------------


             GraphQL Architecture

Client
   │
   ▼
POST /graphql
   │
   ▼
GraphQL Execution Engine
   │
   ▼
Resolvers
   │
   ▼
Database • REST APIs • Kafka

Request Flow Comparison

REST

Client

↓

Multiple Endpoints

↓

Business Logic

↓

Responses



GraphQL

Client

↓

Single Endpoint

↓

Schema Validation

↓

Resolvers

↓

Single Response

1. What is the Main Difference Between REST and GraphQL?

Answer

REST is a resource-based architectural style, while GraphQL is a query language and runtime for APIs.

REST exposes multiple endpoints.

Example

/users

/orders

/products

GraphQL typically exposes a single endpoint.

POST /graphql

Clients decide which fields to retrieve.

2. How Do REST and GraphQL Retrieve Data?

Answer

REST returns predefined resource representations.

Example

GET /users/101

GraphQL

query {

  user(id:101){

      name
      email

  }

}

GraphQL allows clients to retrieve only the required fields.

3. What are Over-Fetching and Under-Fetching?

Answer

REST may return more information than required.

Example

GET /users/101

Returns

Name
Address
Email
Phone
Preferences
Orders

Even if only the name is needed.

GraphQL

{

 user(id:101){

     name

 }

}

Returns only the requested field.

GraphQL also avoids under-fetching by allowing nested object retrieval in a single request.

4. Which One Performs Better?

Answer

Performance depends on the use case.

REST performs well for:

Simple CRUD
CDN caching
Static resources
Public APIs

GraphQL performs well for:

Mobile applications
Complex dashboards
Nested object graphs
Multiple frontend applications
BFF (Backend for Frontend)

There is no universal winner.

5. How Do REST and GraphQL Handle Versioning?

Answer

REST commonly versions endpoints.

/api/v1/users

/api/v2/users

GraphQL usually evolves the schema without introducing new endpoints.

Techniques include:

Deprecating fields
Adding optional fields
Maintaining backward compatibility

6. Which One is Easier to Cache?

Answer

REST integrates naturally with HTTP caching.

Example

Browser cache
CDN
Reverse proxy
ETag
Cache-Control

GraphQL caching is more complex because every query may request different fields.

GraphQL often uses:

Persisted queries
Client-side caches
DataLoader
Redis

7. Which One is More Flexible?

Answer

GraphQL offers significantly more flexibility.

Clients can:

Choose fields
Retrieve nested objects
Combine multiple resources
Reduce network calls

REST responses are predefined by the server.

8. How Do Spring Boot Applications Support Both?

Answer

Spring Boot supports REST using:

Spring MVC
Spring WebFlux

GraphQL support is provided by:

Spring for GraphQL

Example REST

@GetMapping("/users/{id}")

Example GraphQL

@QueryMapping

Both technologies integrate seamlessly with Spring Security, Spring Data, and Spring Boot Actuator.

9. Which One is Better for Microservices?

Answer

REST remains the most common communication mechanism between microservices.

GraphQL is commonly used as:

API Gateway
Backend for Frontend (BFF)
Aggregation Layer

Example

Mobile

↓

GraphQL

↓

Order Service

Customer Service

Payment Service

This reduces the number of client requests.

10. How Do Security Models Differ?

Answer

REST security:

OAuth2
JWT
HTTPS
RBAC

GraphQL requires the same security mechanisms plus:

Query depth limits
Query complexity analysis
Resolver authorization
Introspection control
Rate limiting

GraphQL introduces additional protections because clients control query structure.

11. What are Common REST and GraphQL Mistakes?

Answer

REST mistakes:

Over-versioning
Large payloads
Poor resource naming
Too many endpoints

GraphQL mistakes:

Deep nested queries
N+1 Query Problem
No pagination
Missing DataLoader
Weak authorization

12. When Should REST be Preferred?

Answer

REST is ideal for:

CRUD applications
Public APIs
File downloads
Cache-heavy workloads
Simple integrations
Standard enterprise services

REST is easier to understand and simpler to operate.

13. When Should GraphQL be Preferred?

Answer

GraphQL is ideal for:

Mobile applications
Complex dashboards
Multiple frontend teams
Aggregated APIs
BFF architecture
Frequently changing UI requirements
Real-time applications
Rich client experiences

14. Can REST and GraphQL Work Together?

Answer

Yes.

Many enterprise systems expose REST internally while providing GraphQL externally.

Example

Mobile App

↓

GraphQL Gateway

↓

REST Microservices

↓

Database

This approach allows organizations to modernize without rewriting existing REST services.

15. What Does an Enterprise Hybrid API Architecture Look Like?

Answer

         Mobile • Web • Partner Applications
                      │
          ┌───────────┴───────────┐
          ▼                       ▼
     GraphQL Gateway         REST Clients
          │                       │
          ▼                       ▼
 GraphQL Execution Engine     REST Gateway
          │                       │
          └───────────┬───────────┘
                      ▼
             Spring Boot Services
      ┌───────────────┼────────────────┐
      ▼               ▼                ▼
 Order Service   Payment Service   User Service
      │               │                │
      └───────────────┼────────────────┘
                      ▼
         Database • Kafka • Redis

Enterprise Components

GraphQL Gateway
REST APIs
Spring Boot Services
API Gateway
GraphQL Resolvers
REST Controllers
Database
Cache
Kafka
Monitoring Platform

GraphQL vs REST Summary

Feature	REST	GraphQL
Endpoints	Multiple	Single
Data Retrieval	Fixed	Client-defined
Over-Fetching	Possible	Eliminated
Under-Fetching	Possible	Eliminated
Caching	Excellent	More complex
Versioning	Endpoint-based	Schema evolution
Flexibility	Moderate	High
Learning Curve	Easier	Steeper
Real-Time Support	Requires additional technologies	Built-in subscriptions
Best For	CRUD and public APIs	Complex client applications

Interview Tips

Explain that REST is an architectural style, while GraphQL is a query language and runtime.
Discuss over-fetching and under-fetching as primary motivations for GraphQL.
Compare multiple REST endpoints with GraphQL's single endpoint approach.
Explain why REST is generally easier to cache using standard HTTP mechanisms.
Highlight GraphQL's advantages for mobile applications, dashboards, and Backend for Frontend (BFF) architectures.
Discuss GraphQL-specific concerns such as the N+1 Query Problem, query complexity, and DataLoader.
Explain schema evolution in GraphQL versus endpoint versioning in REST.
Recommend GraphQL gateways for aggregating multiple REST microservices.
Emphasize that both technologies complement each other rather than compete.
Use enterprise examples where REST powers internal services and GraphQL provides a unified API for frontend clients.

Key Takeaways

REST and GraphQL solve API communication problems using different architectural approaches.
REST uses multiple resource-oriented endpoints, while GraphQL typically exposes a single endpoint.
GraphQL eliminates over-fetching and under-fetching by allowing clients to request exactly the required fields.
REST offers simpler caching through standard HTTP mechanisms such as ETags and Cache-Control.
GraphQL provides greater flexibility for mobile applications, dashboards, and rapidly evolving frontends.
Spring Boot supports both REST (Spring MVC/WebFlux) and GraphQL (Spring for GraphQL).
Enterprise architectures often combine GraphQL gateways with existing REST microservices.
GraphQL introduces additional considerations such as query complexity analysis, DataLoader, and resolver security.
Choosing between REST and GraphQL depends on business requirements rather than technology preference.
GraphQL vs REST is one of the most frequently asked interview topics for Java, Spring Boot, Microservices, Cloud, and Solution Architect roles.