10 Microservices Interview Questions Every Developer Must Prepare

The world of software architecture has shifted. The days of the massive, unwieldy monolith are fading fast.

In fact, Gartner reports that 74% of organizations are already using microservices.

That means if you’re stepping into a backend or full-stack interview in 2025, you will face questions on distributed systems.

But here’s the problem: most candidates just memorize definitions.

To stand out, you need to show you understand the trade-offs, the pain points, and the real-world implementations.

Here are 10+ microservices interview questions (and sample answers) to help you crush your next technical round.

1. Monolith vs. Microservices: What’s the real difference?

Sample Answer: A monolith is a single, unified unit where all logic (database, UI, server) lives in one codebase and scales together. Microservices break this into small, independent services that communicate via APIs, allowing teams to scale, deploy, and choose technologies for each service independently.

Don’t just say "microservices are small." Focus on coupling. In a monolith, a bug in the billing module can bring down the entire user dashboard.

In microservices, the billing service might fail, but the user can still browse products. This "fault isolation" is a key selling point.

Also, mention the operational complexity. Microservices aren't free; they trade development simplicity for operational complexity.

Also Read: How to make a Microservices Java resume?

2. How do you handle distributed transactions? (Saga vs. 2PC)

Sample Answer: You generally avoid ACID transactions across services. Instead, use the Saga Pattern, which is a sequence of local transactions. If one fails, you execute "compensating transactions" to undo previous steps. Avoid Two-Phase Commit (2PC) in high-scale systems as it blocks resources and reduces performance.

This question is a favorite for senior roles. You need to explain why 2PC is bad for microservices (it’s a blocking protocol).

• Choreography-based Saga: Services emit events (e.g., "OrderCreated"), and other services listen and react. Good for simple workflows.
• Orchestration-based Saga: A central "Orchestrator" service tells participants what to do. Better for complex workflows with many steps.

If you are a Java developer, you might be familiar with frameworks like Axon or Spring Cloud.

3. What is the Circuit Breaker pattern and why do you need it?

Sample Answer: It’s a design pattern that prevents your application from trying to call a dead service repeatedly. If a service fails too often (hits a threshold), the "circuit opens," and calls fail immediately without waiting for a timeout, protecting the system from resource exhaustion.

Imagine Service A calls Service B. If Service B is down, Service A shouldn't hang for 30 seconds waiting for a response. That delay ripples back to the user.

• Closed State: Traffic flows normally
• Open State: Traffic is blocked immediately (fail fast)
• Half-Open: Allows a few test requests through to check if the service has recovered

Pro Tip: Mention libraries like Resilience4j (for Java) or Polly (for .NET) to show hands-on experience.

4. How do you implement Service Discovery?

Sample Answer: In a dynamic environment (like Kubernetes), IP addresses change constantly. Service Discovery allows services to find each other dynamically. A service registers its instance (IP/Port) with a "Service Registry" (like Eureka or Consul) on startup, and other services query this registry to find it.

Hardcoding URLs (e.g., http://localhost:8080) is a rookie mistake.

• Client-Side Discovery: The client queries the registry and load balances the request itself (e.g., Netflix Ribbon).
• Server-Side Discovery: The client calls a load balancer (like AWS ELB or Nginx), which queries the registry.

Also Read: What are some commonly asked spring boot interview questions?

5. What is an API Gateway?

Sample Answer: It is the single entry point for all client requests. Instead of a client calling five different microservices directly, it calls the API Gateway, which routes the request, handles authentication, rate limiting, and SSL termination, and then aggregates the results.

Using an API Gateway can reduce latency for the end-user by aggregating multiple backend calls into a single round-trip, significantly improving mobile performance.

6. How do you secure Microservices? (OAuth2 & JWT)

Sample Answer: The standard is OAuth 2.0 with OpenID Connect. A central Identity Provider (IdP) issues a JSON Web Token (JWT) upon login. The client sends this token in the Authorization header with every request. Each microservice validates the token’s signature to ensure the user is authorized.

Don't confuse authentication (who you are) with authorization (what you can do).

• Edge Security: The API Gateway often validates the token first.
• Zero Trust: Ideally, services should also validate the token to ensure internal traffic is secure.
• Scopes: Use OAuth scopes (e.g., read:orders, write:profile) to limit what a token can do.

Also Read: How to become a Java developer?

7. What is the "Database per Service" pattern?

Sample Answer: It means each microservice owns its own database and is the only one that can access it. No other service can read/write to that DB directly; they must use the owner service's API. This ensures loose coupling and allows services to choose different DB technologies (Polyglot Persistence).

The Challenge: This makes "joins" impossible at the database level. You have to do "API composition" (fetching data from multiple APIs and combining it in code) or use data replication. This complexity is why strong DBMS interview questions knowledge is vital - you need to know when to use NoSQL vs. SQL for specific microservices.

8. How do you debug and trace requests across services? (Observability)

Sample Answer: You use Distributed Tracing. A unique Trace ID is assigned to an incoming request and passed along to every microservice that handles it. Tools like Jaeger or Zipkin collect these traces, allowing you to visualize the full request flow and pinpoint exactly which service caused the latency or error.

In a monolith, you look at one log file. In microservices, you might have 50 log files. Without a correlation ID (Trace ID), debugging is a nightmare.

• Logs: Tell you what happened.
• Metrics: Tell you trends (e.g., CPU usage).
• Traces: Tell you where it happened.

9. What is the "Strangler Fig" pattern?

Sample Answer: It’s a strategy to migrate a monolith to microservices gradually. You build a new microservice for a specific feature (e.g., "Search") and route traffic for that feature to the new service, while the rest goes to the old monolith. Over time, you "strangle" the monolith until nothing is left.

Never rewrite a monolith from scratch (the "Big Bang" approach). It has a high failure rate. The Strangler Fig pattern allows you to deliver value quickly while modernizing the stack.

10. How do you handle failure? (Bulkhead Pattern)

Sample Answer: The Bulkhead pattern isolates resources so that a failure in one part of the system doesn't crash the whole thing. Just like a ship has compartments, you might use separate thread pools for different services. If the "Image Processing" service fills up its thread pool, the "User Login" service remains unaffected.

Adopting resilience patterns like Bulkhead and Circuit Breakers can improve system availability to 99.99% by preventing cascading failures.

Also Read: What are some common JavaScript interview questions?

Quick-Fire Round: Advanced Concepts

• Q: What is Blue-Green Deployment?A: You run two identical production environments (Blue and Green). You deploy the new version to Green, test it, and then switch the router to send all traffic to Green. Instant rollback is possible.
• Q: What is Eventual Consistency?A: A consistency model used in distributed systems where data will become consistent eventually, but not immediately. It’s the trade-off for high availability (CAP Theorem).
• Q: What is a Sidecar Pattern?A: Deploying a helper service (like a logging agent or proxy) alongside your main application container. Kubernetes uses this heavily (e.g., Envoy proxy in a Service Mesh).

Final Thoughts

When answering these questions, always tie them back to the business value.

You don’t adopt microservices because they’re trendy - you adopt them because they help teams ship faster, scale cleanly, and recover quickly when things go wrong.

If you want to practise these questions the way real interviewers expect, Hiration's interview prep can support you with:

• Instant feedback on structure, clarity, and how well you explain trade-offs
• Job-description based questions so you’re practising with the right level of depth
• Speech analysis to help you refine pace, tone, and filler words
• Body-language insights during video responses
• Answer restructuring suggestions to make your explanations sharper and more confident

Walk in prepared, not just informed.