Most Asked Kafka Interview Questions in 2026
Most Asked Kafka Interview Questions in 2026 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.
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...
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...
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...
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...
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...
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...
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...
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 +...
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...
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...
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...
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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