Kafka Interview Questions for 5 Years Experience

Kafka Interview Questions for 5 Years Experience Work through these 12 questions out loud. Open any question for the full model answer, the trap to avoid, and the follow-up a panel usually asks.

  1. Explain the transactional outbox pattern.

    OrderService @Transactional saves Order and OutboxEvent(type=ORDER_CREATED, payload=json). OutboxProcessor @Scheduled polls FOR UPDATE SKIP LOCKED, sends to Kafka, updates...

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  2. Database sharding strategies for high-scale Java services?

    Shard by tenant_id mod 32 — RoutingDataSource lookup. User-scoped queries single shard. Global admin reports from CQRS read replica or Elasticsearch. Plan shard key early —...

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  3. Kafka consumer groups, offsets, and delivery semantics?

    @KafkaListener with AckMode.MANUAL — ack after DB save. Consumer group order-service scales to partition count max. Idempotency key in message header dedup table. Monitor...

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  4. How would you design a rate-limited REST API?

    API gateway or filter applies token bucket per API key — Redis stores tokens with TTL. Exceeding limit returns 429 + Retry-After. Different tiers per plan. Log rejections for...

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  5. How do you test Spring Boot applications?

    Unit test services with Mockito — no Spring. @WebMvcTest + MockMvc for controller contract. @DataJpaTest for repository queries. @SpringBootTest + Testcontainers for critical...

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  6. How does Micrometer Tracing replace Spring Cloud Sleuth?

    Dependencies: micrometer-tracing-bridge-otel, opentelemetry-exporter-otlp. Traces propagate Authorization-safe headers across RestClient/WebClient calls. Correlate logs with...

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  7. How do you handle long-running background jobs in Spring Boot?

    Do not block HTTP threads. Use `@Async` with named executor or message-driven workers. ```java @EnableAsync @Configuration public class AsyncConfig { @Bean Executor...

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  8. Why does Context re-render every consumer, and how do you keep RBAC/theme from stalling the tree?

    AuthProvider holds user with useMemo. Permission checks go through can(permission) from a hook that reads a stable access object. Theme is a separate provider. High-frequency...

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  9. What is circuit breaker pattern?

    When payment service errors exceed 50% in 10s window, breaker opens — return fallback immediately for 30s. Half-open lets one request through to test recovery. Pair with...

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  10. Compare BlockingQueue implementations for producer-consumer workloads.

    For order processing, use ArrayBlockingQueue with capacity matching SLA — slow consumer blocks producer instead of OOM. ThreadPoolExecutor with SynchronousQueue +...

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  11. What is Spring Boot Docker Compose dev services support?

    Add compose.yaml with postgres and redis services. Include spring-boot-docker-compose on runtimeOnly. Boot starts Postgres, sets JDBC URL — zero local install. CI uses...

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  12. Explain CAP theorem in the context of microservices.

    When a network split isolates nodes, you cannot have both perfect consistency and every node answering. Example: order service during partition — either reject writes (CP) or...

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