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Below are the MOST-ASKED Microservices interview questions with CLEAR, READY-TO-SPEAK answers for 3 years experience.
You can almost memorize + adapt to your project.
1️⃣ What are Microservices?
Answer:
Microservices is an architectural style where an application is broken into small, independent services, each responsible for a single business capability.
Each service is independently developed, deployed, and scaled, and they communicate over lightweight protocols like REST or messaging.
2️⃣ Monolithic vs Microservices
| Monolithic | Microservices |
|---|---|
| Single deployable unit | Multiple independent services |
| Tight coupling | Loose coupling |
| Hard to scale | Easy to scale |
| One tech stack | Different stacks possible |
| Risky deployments | Safe independent deployments |
3️⃣ Advantages of Microservices
Independent deployment
Better scalability
Fault isolation
Faster development
Technology flexibility
Disadvantages
Increased complexity
Network latency
Data consistency issues
Requires DevOps maturity
4️⃣ When should we NOT use Microservices?
Small applications
Simple business logic
No DevOps support
Small team
👉 Monolith is better in such cases
5️⃣ How do Microservices communicate?
Answer:
Synchronous – REST (HTTP/JSON)
Asynchronous – Messaging (Kafka / RabbitMQ)
Most projects start with REST, and use messaging for event-driven communication.
6️⃣ Synchronous vs Asynchronous Communication
| Synchronous | Asynchronous |
|---|---|
| Immediate response | No immediate response |
| Tight coupling | Loose coupling |
| Blocking | Non-blocking |
| REST calls | Kafka / MQ |
7️⃣ What is Service Discovery?
Answer:
Service Discovery allows microservices to dynamically find each other without hard-coding IPs or ports.
Example: Eureka Server
8️⃣ How does Eureka work?
Answer:
Services register with Eureka
Eureka maintains service registry
Clients fetch service list
Load balancing happens on client side
Heartbeats ensure health checks
If Eureka is down → existing services still work using cached registry
9️⃣ What is API Gateway?
Answer:
API Gateway is a single entry point for all client requests. API Gateway is a centralized entry point in microservices that handles routing, security, load balancing, rate limiting, and aggregation of requests before forwarding them to backend services.
Responsibilities:
Routing
Authentication
Rate limiting
Logging
Request aggregation
Client sends request to API Gateway
-
Gateway validates authentication token
-
Applies rate limiting
-
Routes request to target microservice
-
Receives response from service
-
Applies logging / transformation
-
Sends response back to client
🔟 API Gateway vs Load Balancer
| API Gateway | Load Balancer |
|---|---|
| Application level | Network level |
| Handles security & routing | Only distributes traffic |
| Aware of services | Not aware of logic |
1️⃣1️⃣ What is Spring Cloud Config?
Answer:
Spring Cloud Config provides centralized configuration management for all microservices.
Configs are stored in:
Git
SVN
File system
Each service fetches configs at startup.
1️⃣2️⃣ Why centralized config is needed?
Avoid duplication
Easy environment management
No redeploy for config change
Consistent configuration
1️⃣3️⃣ Should microservices share a database?
❌ No
Reason:
Tight coupling
Deployment dependency
Schema changes impact all services
✔️ Database per microservice is recommended
1️⃣4️⃣ What is Eventual Consistency?
Answer:
In microservices, data may not be immediately consistent across services, but it will eventually become consistent.
Used when:
Distributed systems
No global transactions
1️⃣5️⃣ What is a Distributed Transaction?
Answer:
A transaction that spans multiple microservices and multiple databases.
1️⃣6️⃣ Why 2-Phase Commit is not recommended?
Performance overhead
Blocking calls
Poor scalability
Single point of failure
1️⃣7️⃣ What is Saga Pattern?
Answer:
Saga is a way to manage distributed transactions using a sequence of local transactions.
If one step fails → compensating transactions are executed.
1️⃣8️⃣ Saga: Choreography vs Orchestration
| Choreography | Orchestration |
|---|---|
| Event driven | Central coordinator |
| Loose coupling | More control |
| Complex debugging | Easier monitoring |
1️⃣9️⃣ What is Circuit Breaker?
Answer:
Circuit Breaker prevents a service from repeatedly calling a failing service, avoiding cascading failures.
States:
Closed
Open
Half-open
2️⃣0️⃣ Resilience4j vs Hystrix
Hystrix → Deprecated
Resilience4j → Lightweight, Java 8+, preferred
2️⃣1️⃣ What is Load Balancing?
Answer:
Distributing incoming requests across multiple service instances to improve performance and availability.
2️⃣2️⃣ Client-side vs Server-side Load Balancing
| Client-side | Server-side |
|---|---|
| Ribbon | Nginx |
| Client decides | Server decides |
| Uses service registry | Static routing |
2️⃣3️⃣ How do you secure microservices?
API Gateway
OAuth2 / JWT
Token validation
HTTPS
Role-based access
2️⃣4️⃣ JWT vs OAuth2
OAuth2 → Authorization framework
JWT → Token format
JWT is commonly used with OAuth2
2️⃣5️⃣ Where should JWT be validated?
✔️ At API Gateway
Reason:
Centralized security
Avoid duplication
Better performance
2️⃣6️⃣ Logging challenge in Microservices?
Logs are distributed
Hard to trace requests
Solution:
✔️ Centralized logging (ELK)
2️⃣7️⃣ What is Distributed Tracing?
Answer:
Tracking a request as it flows through multiple services.
Tools:
Spring Cloud Sleuth
Zipkin
2️⃣8️⃣ How do you deploy microservices?
Docker containers
CI/CD pipelines
Kubernetes (optional)
⭐ MOST IMPORTANT FINAL QUESTION
“Explain Microservices Architecture in your project”
Structure your answer like this:
Number of services
Communication style
Service discovery
API Gateway
Database strategy
Security
Deployment
If you want, next I can:
🔹 Convert this into one-page revision notes
🔹 Create mock interview Q&A
🔹 Help you fake-proof project explanation (very important 😉)
🔹 Give diagram-based explanation
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