Java Microservices Interview Questions and answers

Is it necessary to be prepared for an interview? The answer is YES! We won’t want to ruin our first impression without being prepared. Let’s get prepared for the Java Microservices Interview with the following questions.

Introduction

‘Microservices’ is an SDLC(Software Development Life Cycle) approach or mainly a service-oriented architecture where applications are constructed by assembling small autonomous functional modules.

1. Why Choose The Microservice Architecture?

Answer:

Issues with the Monolithic architecture:

• Every application is created as a single autonomous program by combining various components such as notification module, and business logic.
• These applications are huge and made by either a single large team or several teams. They all will have to work again in case of any change or deployment.
• It has a huge application code base creating overhead and difficulties to understand the code. Thus, such applications are not updated frequently.
• It focuses on the project as a whole.

Choosing Microservice architecture:

• Since every component has a different team, issues with a single process don’t bother other parts of the application.
• This can be done by big and small teams as well.
• Deployment can be done separately in less time.
• Microservice applications can be updated with the changing technology.
• This architecture is lightweight and understanding the code is comparatively easy.
• It focuses on the product.

2. Explain Spring Cloud And Spring Boot.

Answer:

Spring Cloud:

• Distributed systems contain latency overhead, redundancy, performance issues, security issues, and bandwidth issues.
• These problems can be solved by Spring Cloud.
• JVM applications for the cloud can be easily made, deployed, and handled by Spring Cloud. It is a microservice framework used by developers to build some of the common patterns when it comes to distributed systems. Some examples are one-time tokens, control bus, circuit breakers, and configuration management. They can support any distributed system.
• It also provides service-to-service calls, routing, and load balancing.

Spring Boot:

• Spring has become complex with time. To start a new project, a build path has to be added, dependencies have to be created, and Spring configuration has to be added after configuring the application server.
• Spring Boot comes to the rescue.
• With Spring Boot, developers can build their apps using Java applications through an embedded server.
• Tomcat is used here.
• Some Spring Boot projects are REST Docs, data, framework, batch, cloud, IO platform, security, session, and integration. Thus, Spring Boot has various needed applications.

3. What Are Some Main Features Of Microservices?

Answer:

1. Data management is decentralized. Every service will own the data of its business functionality. Thus, the schema changes in one service won’t affect other services.
2. Complexities of the components are hidden from each other to avoid unwanted dependencies amongst the microservices. Communication between the services occurs through channels or well-defined APIs.
3. Organized according to the business capabilities. Every team is based on expertise in terms of the technology it is working on. In monolithic applications, every team would work on different layers of different services. For example, one team would work on the back-end and another team would work on UI. But according to the microservice architecture, every team will work on a different technology stack(such as registration form or making bills).
4. Application is separated into small individual manageable components. Changes in some components won’t affect a greater part of the code.
5. They support polyglot architecture. Different teams can use different technology stacks for the microservice they are working on. For different microservices,

• Different versions of the same technology can be used.
• Different technologies can be used.
• Different architectures can be used.

6. They support DevOps implementation which means that the team that developed the service is also responsible to maintain its code in production. Thus, fixing an issue can be made easier and faster. The team can have its releases and upgrades.

4. How Does Microservice Architecture Work?

Answer:

Figure: Microservices Architecture

· An application is made up of loosely coupled separate independent modules that perform different functions.

· At the Client Side, there are users sending requests through various devices.

· Identity Providers are present to authenticate the clients and provide security tokens.

· Content Delivery Networks(CDNs) are made up of distributed proxy servers.

· Client requests are handled by the Application Programming Interface(API).

· The Web Application contains the data shown to the client.

· Failures are identified by the Control section. It also balances the services on the nodes.

· To find a route for communication between the microservices, Service Discovery proves to be helpful.

· The client can access only a part of the data needed for him through the Remote Database.

5. What Are Some Popular Java Microservices Frameworks?

Answer:

1. Spring Boot. 
2. Jakarta EE(The classic Java Enterprise Edition). 
3. Dropwizard. 
4. Micronaut.
5. Lagom.
6. Open Liberty.
7. Axon Framework.
8. Spark Java.

6. What Does Actuator Do In Spring Boot?

Answer:

It is a sub-project of Spring Boot that provides RESTful web services. These services help us to access an application’s current state that’s running in production. Various production-grade services are added by it to our applications to reduce our efforts. Various metrics and operations can be managed by this.

7. How Can The Spring Boot Project’s Default Properties Be Overridden?

Answer:

Following properties should be mentioned in ‘application.properties.’

To specify the suffix, write: spring.mvc.view.suffix: .jsp

To specify the prefix, write: spring.mvc.view.prefix: /WEB-INF/

8. How Does The Communication Between Java Microservices Occur?

Answer:

Method 1: Synchronous communication

This can be done using RestTemplate with Ribbon, HTTP, WebClient, FeignClient. But such calls bring delays in the network. Partial failures can be solved by the Hystrix circuit breaker.

Method 2: Asynchronous communication

This method is used when the user doesn’t need an immediate response. The message is sent by the user to the message broker. This can be done through AMQP(or RabbitMQ), JMS implementation, or Kafka.

9. Explain Contract Testing.

Answer:

• An integration point is tested by checking every application separately. The motive of the Contract Testing methodology is to ensure that the separate microservices can easily communicate with each other.
• The interactions exchanged between each service are captured, stored in a contract, and verified by those separate parties.
• For example, if communication between the applications occurs through HTTP, the HTTP request and response would act as the messages. 
• Contract Testing is something more than Schema Testing because in the former case, the parties testing two separate applications have to come together and agree on a common set of rules.

10. When Will Be Contract Testing Useful?

Answer:

• It is mostly useful when there are many services like in the Microservice architecture.
• When two services will want to communicate, Contract Testing will be useful immediately.
• When irregularities in the consumer workflow and configuration have to be detected.

11. What Is PACT In Microservices And How Does It Work?

Answer:

• The open-source tool named ‘PACT’ is implemented through consumer-driven contracts. The JSON files are used to store the outputs of the tests of interactions between the two microservices.
• PACT creates stubs based on the tests created by the developer to test the interactions.
• These tests contain the state of the provider, the request, and the expected response.

Conclusion

On one hand, microservices have become popular since their launch in 2011. On other hand, java has always been famous for the last 30 years. The choice of questions may differ according to the interviewer. Still, an attempt has been made here to provide popular questions for the Java Microservices interview. Detailed courses for the same can be helpful.

Frequently Asked Questions

1. What Are The Disadvantages Of Using Microservices?

Answer:

• The problem in debugging: It is difficult to locate the errors on each service. Maintaining central logs could be helpful here.
• DevOps team: Components built independently using different technologies have to be centralized. This is not an easy task. A skilled DevOps team is needed for that.
• More cost: Since the distributed system is used here, more cost is required for its centralization.
• Synchronization between the independent teams: Though they are working independently, they will have to collaborate at some point in time.
• Automating the components is difficult: The components are smaller and they have to go through building, deployment, and monitoring.
• Configuration issues: The system environment keeps on changing with time. Thus, maintain the configuration every time is difficult.
• The tester should understand the processes. The tester should be well aware of the processes before writing the test cases for integration testing.

2. What Is CDC?

Answer:

Consumer-Driven Contract(CDC) establishes a contract between the service providers and the consumers about the design of the data to be shared. It acts as a pattern to allow the external systems to use the microservices efficiently.

3. What Is Semantic Monitoring?

Answer:

It is also called Synthetic Monitoring. It presents the efficiency of the transaction for the users and the business. A subgroup of the application’s automated tests is executed in live production. On detecting failures, alerts are generated by semantic monitoring.

4. What Are Some Main Tools For Managing Microservice Architecture?

Answer:

1. NGINX.
2. FLUENT.
3. KAFKA.
4. MongoDB.
5. DOCKER.
6. JENKINS.
7. grafana.
8. PROMETHEUS.