400 Microservices Interview Questions with Answers 2026

Communication Patterns: REST, gRPC, Kafka, Circuit Breakers, API Gateways.

Data & Transactions: Saga Pattern, CQRS, Event Sourcing, Eventual Consistency.

DevOps & Observability: Docker, Kubernetes, CI/CD, ELK Stack, Service Mesh.

Security & Readiness: OAuth2, Rate Limiting, Performance Tuning, Fault Tolerance.

B) Using a Distributed Lock Manager (DLM)

C) Implementing the Circuit Breaker pattern

D) Increasing the thread pool size of the calling service

E) Switching from asynchronous to synchronous REST calls

F) Deploying a secondary failover database

Correct Answer: C

Overall Explanation: The Circuit Breaker pattern protects systems by failing fast when a remote service is likely down, preventing resources from being tied up in exhausted threads.

Option A Incorrect: HPA handles load but doesn't stop a failing service from exhausting the resources of its callers.

Option B Incorrect: DLM is for concurrency control/locking, which might actually increase latency and worsen a failure.

Option C Correct: It "trips" the circuit after a threshold of failures, allowing the system to recover or provide a fallback.

Option D Incorrect: Increasing threads often accelerates resource exhaustion (CPU/Memory) during a hang.

Option E Incorrect: Synchronous calls are more prone to cascading failures than asynchronous ones.

Option F Incorrect: Failover databases address data availability, not service communication resilience.

Question 2: When implementing the Saga Pattern to manage distributed transactions across multiple services, what is the primary purpose of a "Compensating Transaction"?

B) To undo the changes made by a previous step if a subsequent step fails

C) To provide a backup of the data in case of a disk failure

D) To encrypt the data during transit between services

E) To synchronize the clocks between distributed nodes

F) To act as a load balancer for the transaction coordinator

Correct Answer: B

Overall Explanation: Since microservices favor eventual consistency over 2PC (Two-Phase Commit), Sagas use compensating transactions to restore the system to its initial state upon failure.

Option A Incorrect: Sagas provide BASE (Basically Available, Soft state, Eventual consistency), not immediate ACID.

Option B Correct: It is a "undo" logic (e.g., "Cancel Order" if "Payment Fails") to maintain business consistency.

Option C Incorrect: This describes data redundancy or backups, not transaction logic.

Option D Incorrect: This describes TLS or transport security.

Option E Incorrect: Clock synchronization is a lower-level networking concern (NTP).

Option F Incorrect: The coordinator manages the flow, but compensation is the specific logic for failure recovery.

Question 3: You are adopting a "Database per Service" pattern. What is the most significant challenge introduced by this architectural choice?

B) Difficulty in implementing foreign key constraints across services

C) Reduced performance of local read operations

D) Simpler CI/CD pipeline configurations

E) Eliminating the need for API Gateways

F) Inability to use Docker containers for databases

Correct Answer: B

Overall Explanation: Decoupling databases ensures service independence but breaks traditional RDBMS referential integrity that spans multiple domains.

Option A Incorrect: While costs might change, the architectural complexity is a much larger hurdle than storage price.

Option B Correct: You cannot join tables or enforce foreign keys across separate databases; this must be managed at the application level.

Option C Incorrect: Local reads are often faster because the database is smaller and specialized for that service.

Option D Incorrect: Pipelines actually become more complex with multiple schemas to manage.

Option E Incorrect: API Gateways are still necessary (and often more important) for routing.

Option F Incorrect: Databases are frequently containerized in development and orchestrated via Kubernetes in production.

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