Top 25 Java Microservices Interview Questions (2024 Updated)

Java microservices have become a popular choice for developing distributed systems. If you’re preparing for a technical interview or looking to improve your understanding of Java microservices, this article has you covered. Here, we’ll provide answers and code snippets for common as well as advanced Java microservices interview questions.

Table of Contents

Common Java Microservices Interview Questions

Q1. What are the key differences between monolithic and microservices architecture in Java-based applications?

Monolithic Architecture:

  • Single, large application with multiple modules.
  • Components are tightly coupled.
  • The entire application must be deployed as a single unit.
  • Difficult to scale and update.
  • Affects overall application performance if any module fails.

Microservices Architecture:

  • Composed of small, independent services.
  • Components are loosely coupled.
  • Each service can be deployed and updated independently.
  • Easier to scale and update.
  • Failure in one service has minimal impact on the overall application.

For a more detailed comparison, check out modernizing monolith to microservices.

Q2. How do you achieve scaling and load balancing in Java microservices?

Scaling and load balancing in Java microservices can be achieved through various methods:

  • Horizontal Scaling: Add more instances of your microservices to distribute the load.
  • Vertical Scaling: Increase the resources (CPU, memory) of your existing microservice instances.
  • Load Balancing: Use a load balancer (e.g., HAProxy, NGINX, AWS Load Balancer) to distribute requests between instances. (Related Reading: AWS ALB vs NLB)
  • Service Discovery: Implement a service registry (e.g., Eureka, Consul) to help load balancers discover available instances.
  • Auto Scaling: Use container orchestration tools like Kubernetes or cloud platforms like AWS to automatically scale instances based on demand.

For more information on scaling microservices, check out Common Microservices Interview Questions and Answers.

Q3. What are the different types of service discovery patterns used in Java microservices, and how do they differ?

There are two main types of service discovery patterns in Java microservices:

  1. Client-Side Discovery: Clients are responsible for discovering and communicating with available services. A service registry (e.g., Eureka, Consul) holds information about available service instances. Clients query the registry and use load-balancing algorithms (e.g., round-robin) to choose a service instance. This approach has lower latency but increased complexity on the client-side.
  2. Server-Side Discovery: A load balancer or API gateway is responsible for discovering and routing client requests to available services. Clients send requests to the load balancer, which queries the service registry and forwards the request to an appropriate instance using load-balancing algorithms. This approach simplifies clients but adds latency due to the additional hop through the load balancer.

For more information on service discovery patterns, check out Top Microservices Frameworks.

Q4. What are the best practices for designing Java microservices APIs, and why are they important?

Designing Java microservices APIs involves following best practices to ensure a consistent, maintainable, and scalable system. Some best practices include:

  1. Use RESTful principles to ensure APIs are stateless, cacheable, and easy to understand.
  2. Version your APIs to avoid breaking changes (e.g., /api/v1/users).
  3. Use standard HTTP status codes for responses.
  4. Implement pagination and filtering for large data sets.
  5. Document your APIs for better collaboration and understanding.

These best practices help maintain a clear and organized system, reducing development time and promoting interoperability between services.

Q5. How do you create a Java-based microservice using Spring Boot? Provide a sample code snippet.

This Question also appears in: Top Microservices Interview Questions and Answers

To create a Java-based microservice using Spring Boot, follow these steps:

  1. Install the Spring Boot CLI or use Spring Initializr to generate a project.
  2. Add the required dependencies (e.g., web, data, actuator).
  3. Create a RESTful API endpoint using @RestController and @RequestMapping.

Sample code snippet:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplicationpublicclassMyMicroserviceApplication {
    publicstaticvoidmain(String[] args) {, args);

@RestControllerclassMyController {
    @GetMapping("/hello")public String hello() {
        return"Hello, Java microservices!";

Q6. How can you use Java’s annotations to define a RESTful microservice using Spring Boot? Provide a code example.

Java’s annotations in Spring Boot allow you to define RESTful microservices using the following:

  • @SpringBootApplication: marks the main class as a Spring Boot application.
  • @RestController: declares a class as a RESTful web service.
  • @RequestMapping: defines the base URI for an endpoint in the class or method level.
  • @GetMapping@PostMapping@PutMapping@DeleteMapping: specify HTTP methods for endpoints.

Code example:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplicationpublicclassMyRestMicroserviceApplication {
    publicstaticvoidmain(String[] args) {, args);

@RestController@RequestMapping("/api")classMyController {
    @GetMapping("/hello")public String hello() {
        return"Hello, RESTful Java microservices!";

Q7. How can you ensure consistency in a distributed Java microservices system using the Saga pattern?

In a distributed Java microservices system, the Saga pattern helps manage transactions that span multiple services. Sagas ensure consistency by compensating for any failed operations.

To implement the Saga pattern in Java microservices:

  1. Break a transaction into a series of local transactions for each involved microservice.
  2. Execute local transactions in a specific order, coordinating with a Saga Orchestrator or using an event-driven approach (e.g., Apache Kafka, RabbitMQ).
  3. Implement compensating transactions to undo previous local transactions in case of failure.
  4. If an error occurs, trigger compensating transactions in reverse order.

The Saga pattern allows for eventual consistency across your Java microservices while maintaining data integrity.

Q8. What are some strategies for handling authentication and authorization in Java microservices?

Some strategies for handling authentication and authorization in Java microservices include:

  1. JSON Web Tokens (JWT): Use JWTs to securely share claims between services. A central authentication service generates JWTs, and each microservice validates the tokens and verifies required permissions.
  2. OAuth 2.0: Use the OAuth 2.0 protocol to authorize access to resources via third-party authorization servers. This strategy is particularly useful for external API integrations.
  3. API Gateway: Authenticate and authorize requests at the API gateway level before forwarding them to microservices.
  4. Spring Security: Use Spring Security’s built-in features (e.g., role-based access control, authentication providers) to secure microservices in Java applications.

For more information on securing microservices, visit AWS EC2 Security: Security Group Facts.

Q9. How can you ensure data resilience and fault tolerance in Java microservices?

To ensure data resilience and fault tolerance in Java microservices:

  1. Implement replication strategies (e.g., master-slave, multi-master) for databases to prevent data loss.
  2. Use distributed databases (e.g., Cassandra, Amazon DynamoDB) that provide built-in data resilience features.
  3. Implement backup and restore mechanisms for databases to handle catastrophic failures.
  4. Use the Circuit Breaker pattern to prevent cascading failures across services (e.g., Spring Cloud Hystrix).
  5. Implement retry logic and timeouts for network calls between microservices.
  6. Monitor health and performance metrics to identify and address issues early.

Q10. What is the role of API gateways in Java microservices, and why are they essential?

API gateways serve as a single entry point for external clients connecting to microservices. Here are some essential roles of API gateways in Java microservices:

  1. Request Routing: Direct client requests to appropriate microservices.
  2. Load Balancing: Distribute requests across multiple instances of a microservice, optimizing resource usage.
  3. Authentication & Authorization: Verify user credentials and permissions before forwarding requests to internal services.
  4. Rate Limiting & Throttling: Control the rate at which clients can make requests, preventing service overload or abuse.
  5. Logging & Monitoring: Collect logs and metrics for monitoring the performance and health of microservices.
  6. Caching: Cache frequently accessed data or responses to improve response times and reduce the load on microservices.
  7. API Composition: Aggregate and transform data from multiple microservices into a single response for the client.

API gateways simplify client interactions with microservices, enhance security, and improve performance and reliability in a distributed system.

Q11. What is the difference between orchestration and choreography in Java microservices?


  • A centrally coordinated approach to managing interactions between services.
  • Typically uses a single orchestrator (e.g., Saga Orchestrator) that controls the overall process.
  • Services are aware of the orchestrator but not of each other.
  • Suited for simple and linear workflows with few dependencies.


  • Decentralized, event-driven approach to managing interactions between services.
  • Each service is responsible for reacting to events from other services and publishing its own events.
  • Peer-to-peer communication between services, without relying on a central coordinator.
  • Suited for complex and dynamic workflows with many dependencies and interactions.

For more information on orchestration and choreography, refer to Web Services vs Micro Services.

Q12. What are the key considerations for handling data consistency and transactions in Java microservices?

Handling data consistency and transactions in Java microservices involves:

  1. Eventual Consistency: Accept eventual consistency instead of strict consistency by using patterns like Sagas or event-driven architectures.
  2. Local Transactions: Keep transactions local to individual microservices, avoiding distributed transactions that span multiple services.
  3. Compensating Transactions: Implement compensating transactions to handle errors and maintain consistency across services.
  4. Idempotent Operations: Design API endpoints to be idempotent, meaning they can be safely retried without causing side effects.
  5. Event Sourcing: Capture changes to the state of a microservice as a sequence of events, supporting consistency and easier troubleshooting.

For more information on data consistency in microservices, read Data Governance Implementation Steps.

Advanced Java Microservices Interview Questions

Q1. How do you deploy and manage Java microservices using Kubernetes? Provide a sample configuration.

To deploy and manage Java microservices using Kubernetes:

  1. Create a Dockerfile to containerize your Java microservice.
  2. Build and push the container image to a container registry (e.g., Docker Hub, Google Container Registry).
  3. Create Kubernetes manifests (e.g., Deployment, Service) to describe your microservice in the cluster.
  4. Use kubectl or CI/CD tools to deploy the manifests to the Kubernetes cluster.

Sample Dockerfile:

FROM openjdk:11-jre-slim
COPY target/my-microservice.jar /app.jarEXPOSE8080ENTRYPOINT ["java", "-jar", "/app.jar"]

Sample Kubernetes configuration (deployment.yaml):


Q2. How do you implement API versioning in Java microservices using Spring Boot? Provide a code example.

To implement API versioning in Java microservices with Spring Boot, use the @RequestMapping annotation to specify different versions for your API endpoints.

Code example:

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestControllerpublicclassApiController {

    @GetMapping("/api/v1/hello")public String helloV1() {
        return"Hello, Version 1!";

    @GetMapping("/api/v2/hello")public String helloV2() {
        return"Hello, Version 2!";

This approach allows clients to request specific API versions, avoiding breaking changes when updating your microservices.

Q3. How do you implement server-side caching in Java microservices using Spring Boot? Provide a code example.

To implement server-side caching in Java microservices using Spring Boot:

  1. Add the spring-boot-starter-cache dependency to your pom.xml or build.gradle.
  2. Enable caching in your Spring Boot application using the @EnableCaching annotation.
  3. Use the @Cacheable annotation on methods that should cache their results.

Code example:

import org.springframework.cache.annotation.Cacheable;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@EnableCaching@RestControllerpublicclassMyController {

    privatefinal MyService myService;

    publicMyController(MyService myService) {
        this.myService = myService;

    @GetMapping("/hello")public String hello() {
        return myService.getHello();

@ServiceclassMyService {
    @Cacheable("hello")public String getHello() {
        // Simulate expensive operationtry {
        } catch (InterruptedException e) {
        return"Hello, cached!";

This example caches the result of the getHello() method, reducing the response time for subsequent requests.

Q4. How does the CQRS pattern apply to Java microservices, and when is it beneficial to use?

Command Query Responsibility Segregation (CQRS) is a pattern that splits read (query) and write (command) operations into separate models or services. It applies to Java microservices in the following ways:

  • Separate Models: Use different data models for reads and writes, optimizing each model for its specific use case (e.g., denormalized views for read operations, normalized models for writes).
  • Separate Services: Create separate microservices for command and query operations, allowing for independent scaling and deployment.
  • Event Sourcing: Combine CQRS with Event Sourcing to capture changes as events and rebuild the state of your microservices from these events.

CQRS is beneficial when:

  • Your system has complex business logic or validation for write operations.
  • You require different performance characteristics for reads and writes (e.g., high read volume but low write volume).
  • You need to scale read and write operations independently.

For more information on CQRS, check out Data Mesh 101.

Q5. How do you implement rate limiting in Java microservices using Spring Boot? Provide a code example.

To implement rate limiting in Java microservices using Spring Boot, use a library like Bucket4j to limit requests using token bucket algorithms.

  1. Add the Bucket4j and Spring Boot starter dependencies to your pom.xml or build.gradle.
  2. Define a rate-limiting filter that uses Bucket4j to enforce rate limits.
  3. Register the filter in your Spring Boot application.

Code example:


import io.github.bucket4j.*;
import org.springframework.web.filter.GenericFilterBean;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

publicclassRateLimitFilterextendsGenericFilterBean {

    privatefinal Bucket bucket;

    publicRateLimitFilter() {
        Bandwidthlimit= Bandwidth.simple(10, Duration.ofMinutes(1));
        this.bucket = Bucket4j.builder().addLimit(limit).build();

    @OverridepublicvoiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
        if (bucket.tryConsume(1)) {
            chain.doFilter(request, response);
        } else {
            HttpServletResponsehttpRes= (HttpServletResponse) response;

Register the filter in

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;

@SpringBootApplicationpublicclassMyRestMicroserviceApplication {
    publicstaticvoidmain(String[] args) {, args);

    @Beanpublic FilterRegistrationBean<RateLimitFilter> rateLimitFilter() {
        FilterRegistrationBean<RateLimitFilter> registrationBean = newFilterRegistrationBean<>();
        return registrationBean;

This example enforces a rate limit of 10 requests per minute for endpoints under /api.

Q6. How do you set up centralized logging for Java microservices using the ELK stack? Provide a sample configuration.

To set up centralized logging for Java microservices using the ELK stack (Elasticsearch, Logstash, and Kibana):

  1. Configure your Java microservice to output logs in JSON format (e.g., using Logstash Logback Encoder).
  2. Install and configure Filebeat to forward logs to Logstash.
  3. Set up Logstash to process logs and send them to Elasticsearch.
  4. Configure Kibana to visualize and analyze logs stored in Elasticsearch.

Sample Logback configuration (logback.xml):

<configuration><appender name="STANDARD_JSON" class="ch.qos.logback.core.ConsoleAppender"><encoder class="net.logstash.logback.encoder.LogstashEncoder"/></appender><root level="info"><appender-ref ref="STANDARD_JSON"/></root></configuration>

Sample Filebeat configuration (filebeat.yml):

filebeat.inputs:-type:logpaths:-/path/to/your/logs/*.logoutput.logstash:hosts: ["localhost:5044"]

Sample Logstash configuration (logstash.conf):

input {
  beats {
    port => 5044

filter {
  # Process JSON logs from Java microservices
  json {
    source => "message"

output {
  elasticsearch {
    hosts => ["localhost:9200"]

This setup allows you to centrally manage logs from multiple Java microservices, improving the monitoring and troubleshooting process.

Q7. How do you implement asynchronous messaging in Java microservices using Spring Boot and RabbitMQ? Provide a code example.

To implement asynchronous messaging in Java microservices using Spring Boot and RabbitMQ:

  1. Add the spring-boot-starter-amqp dependency to your pom.xml or build.gradle.
  2. Configure RabbitMQ connection properties in your Spring Boot application (e.g., application.yml).
  3. Use RabbitTemplate to send messages and @RabbitListener to receive messages.

Code example:

Configure RabbitMQ properties in application.yml:


Create a message producer:

import org.springframework.amqp.core.Queue;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

@ComponentpublicclassMessageProducer {

    @Autowiredprivate RabbitTemplate rabbitTemplate;

    @Beanpublic Queue messageQueue() {

    publicvoidsendMessage(String message) {
        rabbitTemplate.convertAndSend("messages", message);

Create a message consumer:

import org.springframework.amqp.rabbit.annotation.RabbitListener;
import org.springframework.stereotype.Component;

@ComponentpublicclassMessageConsumer {

    @RabbitListener(queues = "messages")publicvoidhandleMessage(String message) {
        System.out.println("Received message: " + message);

This example demonstrates sending messages from a producer to a consumer using RabbitMQ as the message broker.

Q8. How do you configure and use distributed tracing in Java microservices using Jaeger? Provide a sample configuration.

Distributed tracing is essential for monitoring and troubleshooting complex microservices applications. Jaeger is one of the popular distributed tracing systems that can be used with Java microservices.

To configure Jaeger with Java microservices, follow these steps:

  1. Add the Jaeger dependency to your Maven pom.xml or Gradle build.gradle file:
<!-- Maven --><dependency><groupId>io.jaegertracing</groupId><artifactId>jaeger-client</artifactId><version>1.7.0</version></dependency>

// Gradle
implementation 'io.jaegertracing:jaeger-client:1.7.0'
  1. Configure the Jaeger tracer by creating a bean in your Spring Boot application:
import io.jaegertracing.Configuration;
import io.jaegertracing.internal.JaegerTracer;

@ConfigurationpublicclassJaegerConfig {

  @Beanpublic JaegerTracer jaegerTracer() {
  1. Instrument your application using OpenTracing-compatible libraries or manually create spans to trace specific operations in your code.

Q9. How do you implement a circuit breaker pattern in Java microservices using Spring Cloud Hystrix? Provide a code example.

The circuit breaker pattern helps prevent cascading failures in a distributed system by detecting failures and providing fallback responses. Spring Cloud Hystrix is a popular library that implements the circuit breaker pattern in Java microservices.

Here’s how you can implement a circuit breaker using Hystrix:

  1. Add the Spring Cloud Hystrix dependency to your Maven pom.xml or Gradle build.gradle file:
<!-- Maven --><dependency><groupId></groupId><artifactId>spring-cloud-starter-netflix-hystrix</artifactId><version>2.2.10.RELEASE</version></dependency>

// Gradle
implementation ''
  1. Enable Hystrix in your Spring Boot application by adding the @EnableCircuitBreaker annotation to your main class:

@SpringBootApplication@EnableCircuitBreakerpublicclassMyApplication {

  publicstaticvoidmain(String[] args) {, args);
  1. Annotate your methods with @HystrixCommand and provide a fallback method name:

@ServicepublicclassMyService {

  @HystrixCommand(fallbackMethod = "fallbackMethod")public String myMethod() {
    // Your actual method implementation

  public String fallbackMethod() {
    return"Fallback response";

Q10. How can you use the Domain-Driven Design (DDD) approach when developing Java microservices?

Domain-Driven Design (DDD) is an approach to software development that focuses on creating a deep understanding of the domain and its complexities. When developing Java microservices using DDD, you can follow these principles:

  1. Ubiquitous Language: Establish a common language between developers and domain experts that reflects the domain model.
  2. Bounded Context: Define clear boundaries for each microservice based on a specific part of the domain. Each bounded context should have its own domain model and should not be influenced by other contexts.
  3. Entities: Identify the domain entities and their relationships. Entities are objects with an identity that persists over time, such as customers or products.
  4. Value Objects: Create value objects to represent concepts in the domain without an identity, such as money or addresses. Value objects should be immutable.
  5. Aggregates: Organize related entities and value objects into aggregates, which are clusters of objects that form consistency boundaries.
  6. Repositories: Create repositories to manage the persistence of aggregates, abstracting the storage mechanism from the domain logic.
  7. Domain Events: Use domain events to communicate between microservices when a significant change occurs in the domain.
  8. Domain Services: Implement domain services when a behavior doesn’t naturally fit within an entity or value object.

By following these principles, you can create a scalable and maintainable Java microservices architecture that is closely aligned with the business domain.

Q11. How do you create and use custom Spring Boot starters in Java microservices? Provide a code example.

A Spring Boot starter is a convenient way to add dependencies and auto-configuration code to a Spring Boot application. To create a custom Spring Boot starter:

  1. Create a new Maven or Gradle project with a name like my-starter.
  2. Add the required dependencies to your pom.xml or build.gradle file:
<!-- Maven --><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter</artifactId></dependency><!-- Other dependencies required by your starter --></dependencies>

// Gradle
dependencies {
  implementation 'org.springframework.boot:spring-boot-starter'
  // Other dependencies required by your starter
  1. Implement your auto-configuration code in a class and annotate it with @Configuration:
import org.springframework.context.annotation.Configuration;

@ConfigurationpublicclassMyStarterAutoConfiguration {

  @Beanpublic MyComponent myComponent() {
  1. Create a file named spring.factories under src/main/resources/META-INF and add your auto-configuration class:
  1. Package your starter as a JAR file and publish it to a Maven or Gradle repository.

To use your custom Spring Boot starter in a Java microservice:

  1. Add the starter dependency to your pom.xml or build.gradle file:
<!-- Maven --><dependency><groupId>com.example</groupId><artifactId>my-starter</artifactId><version>1.0.0</version></dependency>

// Gradle
implementation 'com.example:my-starter:1.0.0'
  1. Your custom starter’s auto-configuration code will now be automatically executed when the application starts, making its components available for use in the application.

Q12. How do you configure and deploy a Java microservice using Spring Boot on Pivotal Cloud Foundry (PCF)? Provide a sample manifest file and deployment steps.

To configure and deploy a Java microservice using Spring Boot on Pivotal Cloud Foundry (PCF), follow these steps:

  1. Package your Spring Boot application as a JAR or WAR file by running mvn package or gradle build.
  2. Create a manifest.yml file in your project’s root directory with the following content:
applications:-name:my-java-microservicepath:target/my-java-microservice.jar# or build/libs/my-java-microservice.war for Gradlememory:1Ginstances:1buildpacks:-java_buildpackenv:SPRING_PROFILES_ACTIVE:cloud

Replace my-java-microservice with your application’s name and update the path to point to your JAR/WAR file.

  1. Install the Cloud Foundry CLI.
  2. Log in to your PCF account using the CLI:
cf login -a -u your-username -p your-password
  1. Deploy your application by running:
cf push

Your Java microservice will now be deployed and running on Pivotal Cloud Foundry.

Q 13. What are the benefits of using Fargate for Java microservices on AWS?

Using Fargate for Java microservices offers a host of benefits. For instance, it streamlines container management, allowing Java developers to concentrate on writing code and leveraging the rich ecosystem of Java libraries and frameworks. Additionally, Fargate supports seamless scaling and load balancing, ensuring that Java microservices maintain optimal performance and high availability even as the application grows in size and complexity.

Related reading: AWS Interview Questions for Java Developers

Q 14. What are the key steps to successfully deploy a Spring Boot microservice on AWS?

To successfully deploy a Spring Boot microservice on AWS, the key steps involve preparing your microservice for the cloud environment, utilizing AWS services effectively, automating the deployment process, and implementing best practices for security, monitoring, and cost optimization.

Our comprehensive guide on deploying Spring Boot applications to AWS provides a detailed step-by-step process, including how to integrate with AWS services, optimize for performance, and manage costs efficiently, ensuring your Java microservices thrive in the cloud environment.