Microservices - 20 High-Probability Questions with Model Answers

✅ Q1: What is a microservice? How is it different from monolithic architecture?

Your Answer (how you should speak):

A microservice is a small, independent, loosely coupled service that owns its own business logic and data. Unlike monolithic architecture where everything is tightly integrated, microservices are independently deployable and can evolve separately. In my earlier projects, we had separate services like customer order, work order, and order management — each deployed separately and communicating via HTTP clients or messaging queues like RabbitMQ.

Explanation:
They wants to hear: independent, loosely coupled, own data, independently deployable.

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✅ Q2: Why did your previous project move towards microservices?

Your Answer:

Mainly because as the system grew, different modules needed to scale at different levels. For example, customer orders received high concurrent requests, while work orders involved heavy background processing. Microservices allowed us to isolate modules, scale them independently, and work with multiple small teams without impacting each other’s development.

Explanation:
Always tie your answers to scaling, team independence, and evolving features separately.

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✅ Q3: How do microservices communicate with each other?

Your Answer:

We mostly used REST APIs via HTTP Client Factory. Some synchronous calls were made using API clients built as NuGet packages that encapsulated the HTTP calls. For asynchronous communication, RabbitMQ was used to decouple heavy background processing like work order creation or payment status updates.

Explanation:
They want to see that you understand both sync and async options.

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✅ Q4: What are API Clients and NuGet Packages in microservices?

Your Answer:

Instead of each microservice calling REST APIs directly everywhere, we built centralized API clients as reusable NuGet packages. These clients handled HTTP requests, retries, and serialization. Any microservice needing another service would consume its NuGet API Client package, reducing repetitive code and simplifying integration.

Explanation:
This shows your understanding of clean service integration patterns.

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✅ Q5: Why is loosely coupled architecture important?

Your Answer:

Because if one service changes, other services remain unaffected as long as contract (API interface) is not broken. In my projects, if we updated work order logic, customer order microservice didn’t need any code changes.

Explanation:
Core reason behind microservice design.

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✅ Q6: What is service discovery?

Your Answer:

Service discovery allows microservices to dynamically locate each other without hardcoded URLs. In my earlier projects, since deployment was controlled, we often hardcoded stable service URLs. In larger, more dynamic deployments, platforms like Kubernetes provide service discovery using internal DNS.

Explanation:
Explain based on your real scenario, but also show theoretical knowledge.

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✅ Q7: Why do we use message queues in microservices?

Your Answer:

For decoupling. If customer order needs to trigger work order, it doesn’t need to wait for work order processing to complete. Instead, it posts a message to RabbitMQ, and work order service processes it independently, improving system resilience and performance.

Explanation:
Shows you understand asynchronous design properly.

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✅ Q8: Why RabbitMQ? Could you use Azure Service Bus?

Your Answer:

RabbitMQ was already part of the system stack when I joined. It’s lightweight, open-source, and easy to set up for simple pub-sub models. But Azure Service Bus would have provided more enterprise features like DLQs, sessions, and better transactional support.

Explanation:
Show you understand alternatives.

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✅ Q9: How do you handle versioning in your microservices?

Your Answer:

We version our APIs by URL versioning like /api/v1/orders. For major breaking changes, we release a new versioned API while keeping older versions for backward compatibility.

Explanation:
This is the standard approach they expect.

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✅ Q10: How do you handle failures in microservice calls?

Your Answer:

We use resilience patterns — retries for transient failures, circuit breakers to avoid hammering unhealthy services, and timeouts to fail fast. For example, when payment service was temporarily failing, retries with exponential backoff helped avoid unnecessary downtime.

Explanation:
Always bring resilience patterns.

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✅ Q11: What is circuit breaker pattern?

Your Answer:

If a downstream service fails continuously, circuit breaker opens to prevent further calls temporarily. This protects the system from overload and allows dependent services to recover gracefully.

Explanation:
One of the most common UKG questions.

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✅ Q12: What is fallback pattern?

Your Answer:

If one service fails, we serve cached or default data instead. For example, if pricing service failed, we temporarily displayed previous prices fetched from cache while downstream service recovered.

Explanation:
They want to see graceful degradation.

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✅ Q13: Why do you need distributed logging in microservices?

Your Answer:

Since services are decoupled and may fail at different points, centralized logging using tools like ELK stack helps trace complete request flow across services for debugging and monitoring.

Explanation:
Interviewer loves observability questions.

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✅ Q14: How did you scale your microservices?

Your Answer:

Horizontally. Customer order APIs handled multiple user requests, so we scaled by adding more instances behind load balancer. Background jobs like Elasticsearch syncs were vertically scaled with bigger compute resources due to heavy processing.

Explanation:
Always differentiate horizontal vs vertical scaling with examples.

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✅ Q15: What is eventual consistency?

Your Answer:

In microservices, not all updates happen instantly across systems. Some operations may succeed later via retries or message queues, causing temporary inconsistency but eventual correctness.

Explanation:
Very common design interview question.

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✅ Q16: Can microservices share databases?

Your Answer:

Ideally no. Each microservice should own its database to maintain independence. In some of our earlier systems, we had schema-level separation inside a shared database, but the goal was to eventually isolate them.

Explanation:
UKG will love that you’re aware of best practice even if legacy system wasn’t ideal.

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✅ Q17: Why did you use NuGet Packages instead of direct HTTP calls?

Your Answer:

It reduces repetitive code, centralizes API contracts, makes integration cleaner, and version upgrades easier without breaking multiple consumers.

Explanation:
Shows clean architecture understanding.

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✅ Q18: How did you secure microservices?

Your Answer:

We used Azure AD-based authentication on frontend, and generated JWT tokens. Inside APIs, we validated JWT using middleware, and used role-based authorization at controller level to restrict access.

Explanation:
Security comes up in nearly every system design round.

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✅ Q19: What is orchestration vs choreography?

Your Answer:

Orchestration uses a central coordinator to control workflow (ex: Durable Functions). Choreography relies on services reacting to events independently using pub-sub (ex: RabbitMQ, Kafka).

Explanation:
They may throw this word.

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✅ Q20: What do you mean by idempotency in microservices?

Your Answer:

Idempotent operations give the same result even if the request is executed multiple times. For example, if a payment confirmation API is retried, it won’t create duplicate transactions.

Explanation:
Very common in payment systems.

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Boom!
You now have 20 fully prepared microservices questions with exact model answers.