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Java Microservices Kafka

2 weeks ago

London, Greater London, United Kingdom Natobotics Full time

The focus will be on Java microservices (6+ years), Kafka (3+ years), private cloud, and hands-on implementation skills.

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1. Core Java & Advanced Concepts

Be prepared for implementation-based and scenario-driven questions.

Strings & Immutability

  • Difference between String, StringBuilder, and StringBuffer.
  • Why is String immutable in Java?
  • How to create a custom immutable class (implement step by step).
  • Memory allocation for Strings (String Pool vs Heap).

Serialization

  • What is serialization and deserialization?
  • How to make a class serializable?
  • transient and serialVersionUID usage.
  • How serialization impacts performance and when to avoid it.

Concurrency & Multithreading

  • Explain synchronized, volatile, and ReentrantLock.
  • What is the Lock interface and how it differs from synchronized.
  • Difference between BlockingQueue, ConcurrentHashMap, and traditional collections.
  • What is a deadlock and how to prevent or detect it (practical scenario).
  • Thread pool and ExecutorService usage in microservices.
  • Callable vs Runnable.

⸻

2. Microservices Architecture

  • Explain what microservices are and where you have implemented them.
  • Describe real project(s) where microservices were used (especially in Mastercard-like environments).
  • How microservices communicate (REST, gRPC, message queues).
  • How to manage configuration, scaling, and deployment on a private cloud.
  • Explain how you handle inter-service communication, fault tolerance, and circuit breakers (Hystrix, Resilience4j).
  • API Gateway and service registry (Eureka, Consul, etc.).
  • Authentication & Authorization in microservices (OAuth2, JWT, Spring Security).

⸻

3. Kafka (3+ Years Expected)

  • Explain how you used Kafka in your projects (data pipelines, async communication, event sourcing, etc.).
  • Kafka Producer–Consumer model.
  • Partitions, offsets, and consumer groups.
  • How you ensure exactly-once delivery or handle duplicates.
  • Kafka Streams and message ordering.
  • Integration of Kafka with Spring Boot microservices (Spring Kafka).
  • Performance tuning and troubleshooting Kafka lag.

⸻

4. Frameworks & Tools

Spring Framework (Core + Boot)

  • Spring Boot annotations (@RestController, @Configuration, @Component, @Service, etc.).
  • Dependency Injection & Inversion of Control.
  • RESTful APIs and exception handling.
  • Spring Data JPA & transaction management.
  • Spring Security (Authentication & Authorization).
  • Profiles and property management for different environments (private cloud setups).

Executive Framework (if referring to frameworks like ExecutorService or Spring Task Executor)

  • Thread management via Executor framework.
  • Asynchronous task execution.

⸻

5. Design Patterns & Architecture

  • Common patterns used in your implementation:
  • Singleton, Factory, Builder, Prototype, Strategy, Observer, etc.
  • Microservice-related: Circuit Breaker, Gateway Aggregation, Saga, CQRS.
  • When and why you used each.
  • Have you implemented any custom design pattern or reusable utility component?

⸻

6. Problem-Solving / Scenario-Based Questions

  • How would you search or filter based on multiple criteria (e.g., search customers by ID, name, location)?
  • How to optimize search (indexes, pagination, caching).
  • How you handle failed transactions or partial updates.
  • How to debug microservice issues in distributed systems.

⸻

7. Agile & Team Collaboration

  • Are you following Agile Scrum? Describe sprint cycles, ceremonies (daily stand-up, retrospective, grooming).
  • How do you understand user stories and break them into technical tasks?
  • How do you estimate tasks and manage backlog?
  • How do you handle technical debt and backlog cleanup?

⸻

8. Project & Work Environment

  • Describe day-to-day activities (development, review, deployment, production support).
  • Team size and roles.
  • Tools used: Git, Jenkins, JIRA, SonarQube, etc.
  • CI/CD pipeline experience.
  • Monitoring & logging (ELK, Splunk, Prometheus, Grafana).

⸻

9. Security

  • Difference between authentication and authorization.
  • How to secure REST APIs (OAuth2, JWT).
  • How to manage secrets/configurations in private cloud (Vault, KMS, config server).
  • HTTPS/SSL setup in Spring Boot.

⸻

10. Personal & Role-Fit

  • This role is for a sound technical person who can work independently → Be ready with examples showing ownership.
  • How you handle ongoing projects, backlog work, and production issues.
  • How you contribute to team improvement (code reviews, mentoring, refactoring).