Top Microservices Interview Questions to Expect in 2023 - Best Practices by IQCode

Understanding Microservices in Software Development

Microservices, also known as Microservices Architecture, is an approach to software development where large applications are built as a collection of small, independent functional modules. This architectural concept is widely adopted in software development as it facilitates easy maintenance, faster development, and reliable delivery of large, complex applications. The following are the main features of microservices:

* The services are maintainable and testable. * They are loosely coupled, meaning that changes to one service do not affect the others. * Each service is independently deployable. * The services are designed or organized around business capabilities. * They are managed by a small team.

Microservices architecture is a popular approach to developing complex applications. A microservice is a small, independent service that performs a specific function within the overall system. The main components of microservices are:

1. Service Registry <br>
2. API Gateway <br>
3. Configuration Server <br>
4. Monitoring <br>
5. Service Mesh <br>
6. Load Balancer <br>
7. Database <br>
8. Caching <br>
9. Messaging <br>
10. Security

Let's briefly discuss the role of each component in a microservices architecture:

1. Service Registry - This component keeps track of all the available microservices instances in the system.

2. API Gateway - It is an entry point for external clients to the microservices system. It manages the traffic flow and can handle common functionalities like authentication, authorization, and rate limiting.

3. Configuration Server - This component centralizes all the configuration settings of microservices for the entire system.

4. Monitoring - As the name suggests, this component monitors the performance of the microservices and gathers metrics to facilitate debugging.

5. Service Mesh - This is a dedicated infrastructure layer designed to handle communication between microservices.

6. Load Balancer - This component balances the request load on multiple instances of the same microservice.

7. Database - Every microservice can have its own database or can share a common one.

8. Caching - Caching improves the performance of a microservice by storing frequently accessed data in the memory.

9. Messaging - This component helps in building asynchronous communication between microservices.

10. Security - It is an integral part of the microservices architecture to ensure the safety of the system.

Benefits and Drawbacks of Microservices

Microservices are a way to structure applications as a collection of small, independent services that work together to provide a larger, cohesive application. Here are some of the benefits and drawbacks of using microservices:


  • Scalability: Because each microservice is independent, it is easy to scale specific parts of the application without affecting the others. This can lead to improved performance and better resource utilization.
  • Flexibility: Microservices allow for greater flexibility and resilience in the face of change. Because each service is independent, changes can be made to one service without affecting the others.
  • Technology Diversity: Microservices can be written in different programming languages and use different data storage technologies, allowing developers to choose the best tool for each job.
  • Improved Development Efficiency: Because microservices are smaller and more focused, development teams can work on them independently and bring them to market faster.


  • Complexity: Managing a large number of microservices can be complex, as it requires coordinating between multiple teams and services.
  • Deployment and Testing: Deploying and testing a large number of microservices can be challenging, as it requires managing multiple environments and dependencies.
  • Operational Overhead: Running and monitoring a large number of microservices can be expensive and time-consuming, as it requires more infrastructure and monitoring tools.
  • Service Interdependence: If a service is dependent on other services, it can become difficult to identify and resolve issues when they occur.

Three Common Tools Used for Microservices

1. Docker<br>
2. Kubernetes<br>
3. Consul<br>

Microservices architecture is becoming increasingly popular in software development. While implementing microservices, developers rely on several tools and technologies to aid in development, testing, and deployment. Among these tools, the following are the most commonly used:

  • Docker: A containerization platform that allows developers to package and deploy their applications along with all necessary dependencies.
  • Kubernetes: An open-source container orchestration platform to automate deployment, scaling, and management of containerized applications.
  • Consul: A service discovery tool that is commonly used to manage the dynamic network of services in microservices architecture and help discover and connect services to one another.

These three tools provide the necessary infrastructure and tooling to allow developers to build scalable, resilient, and easily manageable microservices applications.

Working of Microservice Architecture

Microservice Architecture is a software development approach that focuses on building small, independent components with specific business functionality that communicate with each other through APIs. Here is how it works:

1. Each microservice is responsible for one specific business capability or function.

2. These microservices communicate with each other through well-defined APIs, making it easy to combine them into larger systems.

3. Each microservice can be developed, tested, deployed, and scaled independently, allowing for greater agility and flexibility in software development.

4. Microservices are deployed in containers, which simplify the process of managing dependencies and reduce the impact of changes in one microservice on the entire system.

5. Monitoring and managing microservices can be challenging, but there are a variety of tools and approaches available to help organizations do this effectively.

Overall, microservice architecture provides developers with a more scalable, flexible, and resilient way to build software systems. By breaking down monolithic applications into smaller, more focused components, it makes it easier to make changes, scale applications, and respond to changing business requirements.

Differences between Monolithic, SOA and Microservices Architectures

Monolithic architecture is an approach where all the components of an application are tightly coupled and interconnected, making it difficult to scale or make changes to individual components. Service-Oriented Architecture (SOA) is an architecture that focuses on loosely coupled services, allowing for greater flexibility and scalability. Microservices architecture is a type of SOA where an application is broken down into small, independent services, each with its own defined function and able to be easily replaced or modified.

The key differences between these architectures are:

  • Coupling: Monolithic architectures have tightly coupled components, while SOA and Microservices have loosely coupled services
  • Scalability: Monolithic architectures are difficult to scale, while SOA and Microservices can be scaled easily by adding more services
  • Flexibility: Monolithic architectures are inflexible, while SOA and Microservices architectures are designed to be flexible, allowing for easier modifications and updates
  • Development: Monolithic architectures require more time and effort to develop, while SOA and Microservices can be developed faster and more easily
  • Cost: Monolithic architectures can be more costly to maintain, while SOA and Microservices architectures can be more cost-effective, especially when it comes to scaling
Overall, the choice of architecture depends on the needs and goals of the application.

Understanding Spring Cloud and Spring Boot

Spring Boot is a framework that is designed to simplify the process of building and deploying applications. It is built on top of the popular Spring Framework and provides a number of features that help you get up and running quickly.

Spring Cloud, on the other hand, is a set of tools and frameworks that help you build cloud-native applications. It provides features such as service discovery, configuration management, and circuit breakers, which are essential when building applications that run on distributed systems.

Both Spring Boot and Spring Cloud are often used together to create microservices-based architectures. Spring Boot helps to create individual microservices, and then Spring Cloud provides the tools to manage them as a set of services. When used together, Spring Boot and Spring Cloud can help to dramatically boost developer productivity and make it much easier to build scalable, resilient, and efficient cloud-native applications.

The Role of Actuator in Spring Boot

Actuators in Spring Boot provide a way to monitor and interact with your application. They expose a set of endpoints that can be used to view information about the application's health, metrics, configuration, and more. This information can be helpful in understanding how your application is performing and troubleshooting any issues.

Actuators are implemented as Spring Boot starter dependencies, so adding them to your project is as simple as adding the appropriate dependency to your build file. Once added, you can access the available endpoints through HTTP requests or via a JMX client.

Overall, the actuator in Spring Boot provides a valuable tool for monitoring and managing your application, making it easier to ensure that it's running smoothly.

Overriding Default Properties in Spring Boot Projects

In Spring Boot projects, the default properties can be easily overridden using the or application.yml file. Here are the steps to override default properties:

1. Create a new file named or application.yml in the src/main/resources directory of your project (if it does not already exist). 2. Add the properties that you want to override with their new values in this file. For example, if you want to change the server port, add the following line to the file:


3. Save the file.

When you run your Spring Boot project, it will pick up the new values from the or application.yml file instead of the default values.

Note that you can also specify the location of the external properties file using the `spring.config.location` property. This can be useful if you want to keep your configuration separate from the application code.

Overall, overriding default properties in Spring Boot projects is a simple process that provides flexibility and customization options for developers.

Solving Issues with Spring Cloud

Spring Cloud solves several common issues faced by developers in distributed systems such as service discovery, load balancing, fault tolerance, configuration management, and more. It provides a set of tools and frameworks for building resilient and scalable microservices. With Spring Cloud, developers can focus on writing business logic and let the framework handle the rest.

Understanding Cohesion and Coupling in Software Engineering

In software engineering, cohesion refers to the measure of how strongly related and focused the functions or modules of a program are, towards a specific task or goal. The higher the cohesion, the better organized and maintainable the code is, and the easier it becomes to make changes if necessary.

On the other hand, coupling refers to the level of dependency between various modules or components of a program. High coupling indicates that changes made to one module may have a significant impact on other modules, making the code difficult to modify and maintain. In contrast, low coupling means that modules are somewhat independent, and changes made in one module won't have much effect on the others.

In general, it is desirable to have high cohesion and low coupling when developing software applications. This helps to ensure that the program is more manageable, scalable, and adaptable to changes over time.

Bounded Context: What does it mean?

In software design, a bounded context is a specific boundary within which a software system operates, with its own rules, constraints, and limitations. It is a key concept in domain-driven design (DDD), which emphasizes breaking down complex systems into smaller, more manageable parts.

The idea is to define clear boundaries between different parts of a system, so that changes made to one part do not affect the other parts. This helps to keep the codebase modular, making it easier to maintain and update.

By defining bounded contexts, developers can focus on specific parts of the system and work on them independently, without worrying about how they will affect the rest of the system. This makes it easier to develop and test software, and can lead to more flexible, adaptable systems over time.

Fundamental Characteristics of Microservice Design

Microservice design has several fundamental characteristics that distinguish it from other architectural styles. These include:

1. Decentralization: Microservice architecture promotes decentralized design where each service is independent of others and can be developed and deployed separately.

2. Autonomous: Each microservice has its own unique business context and is responsible for its own data storage, processing, and business logic.

3. Single Responsibility Principle (SRP): This principle states that a microservice should have one and only one reason to change.

4. Resiliency: Microservices are designed to be resilient to failures and errors by implementing appropriate fault-tolerance mechanisms.

5. Scalability: Microservices can be scaled independently of each other, allowing for greater flexibility in resource allocation.

6. API-based communication: Microservices communicate with each other via standardized APIs, making it easier to manage and maintain the system.

7. Continuous Delivery (CD) and Continuous Integration (CI): Microservices are designed to support CD and CI, enabling faster deployment and releases.

By adhering to these fundamental characteristics, microservice design can help organizations achieve better agility, scalability, and maintainability of their software systems.

Common Challenges When Implementing Microservices

When implementing microservices, there are a few common challenges that one may face:

- Managing the complexity of a distributed system
- Ensuring each service maintains its autonomy
- Implementing effective communication between services
- Ensuring each service is scalable and fault-tolerant
- Managing data consistency and ensuring each service has the appropriate level of access to data
- Implementing appropriate security measures to protect the system and sensitive data
- Testing and debugging a distributed system can be more challenging than testing a monolithic application

Explanation of Pact in Microservices

In microservices architecture, each service is developed and deployed independently. Therefore, it is essential to ensure that all services can communicate with each other without any issues. This is where Pact comes in as a testing framework for microservices.

Pact is a contract testing framework that ensures all services are compatible with each other. Contract testing is different from traditional testing, which generally involves testing the entire system. Instead, Contract testing involves testing the interactions between independent services.

With Pact, developers can create a contract that includes the expected response of one service to another. It ensures that the service calling the other service receives the expected response, and the service providing the response receives a request that it can understand.

Pact enables developers to test interactions between microservices without running them in an integrated environment. This makes the testing process more efficient and less time-consuming.

Overall, Pact is a powerful tool for microservices architecture that helps developers ensure service compatibility and reduce integration issues.

Communication between Independent Microservices

In a microservices architecture, independent services communicate with each other through APIs (Application Programming Interfaces). Each microservice exposes its own API which follows a clearly defined interface specification such as REST (Representational State Transfer).

When one microservice wants to communicate with another microservice, it sends an HTTP request to the exposed API of that microservice. The request contains the necessary information to invoke the desired operation. The other microservice receives and processes the request, and then responds with the appropriate data.

This type of communication allows for greater flexibility and scalability as each microservice can be developed and deployed independently, without affecting the functionality of other microservices. However, proper API design and documentation is crucial for ensuring seamless communication between microservices.

Definition of Client Certificates

Client certificates are a type of digital certificate that are used for authentication purposes. They are issued to individual users or devices, and contain information about the owner and the organization that issued the certificate. Client certificates are used in secure communication protocols such as HTTPS to establish a secure connection between a client (such as a web browser) and a server. They help to ensure that only authorized users or devices can access a particular resource or service.

Famous Companies that Use Microservice Architecture

There are several well-known companies that have adopted microservice architecture including:

1. Netflix 2. Amazon 3. Uber 4. Airbnb 5. Spotify 6. eBay 7. Twitter 8. SoundCloud 9. PayPal 10. Groupon

These companies have successfully leveraged the benefits of microservices such as scalability, fault tolerance, and agility to enhance their overall application performance and business competitiveness.


One question that you may encounter during a microservices job interview is:

What is semantic monitoring?

Semantic monitoring is a technique of monitoring the microservices systems that goes beyond traditional monitoring of system metrics. It involves monitoring the business-level semantics of the microservices system to understand and detect issues that affect overall business functionality. It helps to detect problems related to performance, security, functionality, and other aspects that might affect the business. Semantic monitoring can help to identify and troubleshoot issues before they cause serious damage to the business.

In essence, semantic monitoring helps ensure that the microservices architecture is working as it should to provide value to the business owners. It helps ensure that all the individual microservices are functioning correctly and are communicating effectively with each other.

Continuous Monitoring - Explanation

Continuous monitoring is the practice of tracking and measuring a system's performance and security on an ongoing basis. It involves gathering data at regular intervals and analyzing it to identify potential issues or threats. The goal of continuous monitoring is to detect problems as they arise instead of waiting for them to cause significant damage. This approach helps to minimize the risk of data breaches, downtime, and other disruptions that can impact organizations. Continuous monitoring also helps businesses to meet compliance requirements and improve their overall security posture by providing real-time information about their systems.

What is Domain Driven Design?

Domain Driven Design (DDD) is an approach to software design and development that focuses on understanding the domain or the problem area that a software application is meant to address. The goal of DDD is to create a model of the domain that accurately reflects its intricacies and complexities, and to use this model to drive the design and implementation of the software system.

In DDD, the focus is on the business logic of the application, rather than the technical details of the implementation. This means that the design of the system is driven by the requirements of the business, rather than by the limitations of the technology used to implement it.

DDD also encourages collaboration between domain experts, developers, and other stakeholders in the software development process, to ensure that everyone has a clear understanding of the domain and its requirements. This helps to reduce misunderstandings and errors, and leads to a more effective and efficient development process.

Overall, DDD is a powerful approach to software design and development that can help to create more robust, scalable, and maintainable applications that more closely align with the needs of the business they are meant to serve.

Explanation of Distributed Transaction:

A distributed transaction involves multiple transactions that are executed on multiple databases, which are connected over a network. These transactions work together as a single logical transaction, with the outcome of the entire operation depending on the success or failure of each individual transaction. This type of transaction is commonly used in large-scale applications where data is stored across multiple locations. The coordination of these transactions is typically managed by a distributed transaction manager, which ensures that all parts of the transaction are executed or rolled back as necessary.

Idempotence and Its Usage

Idempotence is the property of an operation where repeating the same operation multiple times produces the same result. In other words, an idempotent operation can be applied multiple times without affecting the result beyond the initial application.

In the context of API design, idempotence is a desirable property for certain types of operations. For example, if a POST request is idempotent, it means that sending the same request multiple times will not result in unintended side effects. This is desirable because in many cases a client may need to retry a failed request, or a network issue may result in the request being sent multiple times.

Idempotence is often achieved by giving the request a unique identifier, such as an IDempotency key, which allows the server to recognize duplicate requests and respond with the same result as the original request.

Ensuring idempotence can improve the reliability and consistency of an API, as it reduces the chances of unintended side effects and makes it easier for clients to recover from failures.

End-to-End Microservices Testing Explained

End-to-end microservices testing refers to the process of testing the communication and functionality between multiple microservices in an application as a whole. This type of testing ensures that all the interconnected microservices are functioning as expected and communicating with each other properly. It typically involves testing each service individually in isolation, then testing the entire system as a whole to ensure all the services work together seamlessly. This type of testing helps to identify and prevent issues that may arise due to miscommunication or errors between microservices, ensuring a reliable and high-quality application.

Explanation of Eureka in Microservices

In microservices architecture, Eureka is a service registry that is used for locating services in the network. It is a component of Netflix's OSS (Open Source Software) suite, and is responsible for registering and tracking the status of microservices instances.

Once a microservice is up and running, it registers itself with the Eureka server and provides information about its location, including its IP address, port number, and metadata such as its health status and other service information. Other microservices that need to communicate with the registered microservice can use Eureka to locate it, instead of hardcoding its IP address and port number in their code, which makes the services more resilient to changes and easier to manage.

Eureka also tracks the status of microservices instances and removes them from the registry if they fail to respond to periodic heartbeats. This way, other microservices consuming the service can be notified of the failed instance and take appropriate action, such as redirecting the traffic to a different instance.

Implementing Service Discovery in Microservices Architecture

In a microservices architecture, service discovery is a crucial component for the communication between services. Here are the steps to implement service discovery:

1. Choose a service registry: A service registry is a database that holds the metadata of all the available services. Popular choices are Consul, Eureka, and Zookeeper.

2. Register services: Each microservice should register itself with the service registry upon startup. The service should include its name, IP address, and port number. This step ensures that the service is discoverable by other services.

3. Discover services: When one microservice wants to communicate with another, it queries the service registry to discover the location of the desired service. The service registry responds with the IP address and port number of the requested service.

4. Load balancing: The service registry can also be used for load balancing. When multiple instances of a microservice are registered with the service registry, the registry can direct traffic to the least busy instance.

By implementing service discovery, microservices can easily locate and communicate with each other, resulting in a scalable and fault-tolerant architecture.

Importance of Reports and Dashboards in Microservices

Reports and dashboards are essential components of any microservice architecture. They provide visibility into the performance and status of microservices, which is critical for maintaining and improving the overall system.

Reports and dashboards allow developers and operators to monitor key metrics, track performance trends, and identify potential issues before they become major problems. This helps to ensure that the microservices are performing as expected and that the entire system is running smoothly.

Additionally, reports and dashboards are useful for communicating the status of the microservices and overall system performance to stakeholders, such as management, customers, or other teams. This visibility helps to build trust in the system and can facilitate better decision-making for all parties involved.

In summary, reports and dashboards are vital for maintaining the health and performance of microservices and for communicating the status of the system to stakeholders.

Reactive Extensions in Microservices

Reactive Extensions (Rx) is a library that allows asynchronous programming and is useful in microservices architecture. This library provides a way to write asynchronous and event-driven code using Observables, which can help in handling incoming requests in microservices.

In a microservices architecture, services can receive a large number of requests that need to be handled efficiently. Reactive Extensions can help with this by allowing services to respond to events coming from various data sources such as databases, message queues, or other services, and in turn, handle the incoming requests in a more responsive and scalable way.

Rx can also be used for composing and transforming streams of data efficiently. It can work seamlessly with other asynchronous frameworks such as Akka, and can be integrated into microservices built on different platforms and languages.

Overall, Reactive Extensions can be a useful tool for building responsive and scalable microservices that can handle large numbers of requests efficiently.

Types of Tests commonly used in Microservices

Microservices architecture has gained popularity due to its ability to help organizations quickly develop and deploy new features and updates. However, with the increasing complexity of microservices, it's important to have a solid testing strategy in place. Generally, the following types of tests are commonly used for microservices:

1. Unit Tests - These are used to test individual pieces of code, usually at the function level, to ensure that each unit is working as expected.

2. Integration Tests - These tests ensure that different services can communicate with each other and work together seamlessly in a real-world scenario.

3. Component Tests - These are used to test individual components of a microservice, including the APIs, databases, and messaging systems.

4. Contract Tests - These tests ensure that the contracts between different microservices are adhered to, and they can communicate with each other without any issues.

5. End-to-End Tests - These tests simulate a complete user interaction with the microservice and its related components to ensure that the application performs as expected in a real-world scenario.

Overall, a combination of these tests is critical to ensure that microservices are functioning as intended and meet the business requirements.

Understanding Mike Cohn's Test Pyramid

Mike Cohn's Test Pyramid is a model for software testing that emphasizes the importance of having a balanced approach to testing. The pyramid consists of three layers:

1. Unit Tests: This layer focuses on testing individual units or components of the software. It involves testing small sections of code to ensure they work as expected.

2. Integration Tests: This layer focuses on testing how the individual components work together as a group. It involves testing the integration of different units and verifying that they function correctly.

3. End-to-End Tests: This layer focuses on testing the entire software system from start to finish. It involves testing the software in a realistic environment to ensure it meets the requirements and performs as expected.

The Test Pyramid helps in planning and executing software tests in a structured and balanced way, ensuring that you cover all aspects of the software and prevent issues from emerging later on in the development cycle.

Understanding Containers in Microservices Architecture

In a microservices architecture, a container is a lightweight and executable software package that comprises code, runtime, system tools, libraries, and settings required to run a service. Containers are isolated from their hosting environment and each other, allowing applications to be rapidly deployed, scaled, and updated without causing disruptions to other services.

Containers provide consistent runtime environments, eliminating the need for developers to depend on different environments during development and deployment. This makes it easier to develop, test, and deploy microservices. Containers are also highly portable, which makes it easy to move them between different development and production environments.

In microservices, containerization is an essential aspect of DevOps. By using containers, developers can focus on writing code while operations teams can take care of container orchestration, deployment, scaling, and monitoring. This separation of responsibilities allows faster development and better agility.

The Significance of Docker in Microservices

Docker plays a critical role in the implementation of microservices architecture. It is a platform that allows developers to deploy, run, and manage applications in containers. Containers are lightweight and portable, making it easy to move and scale microservices across multiple environments. Docker provides a consistent environment, reducing the risk of compatibility issues across different machines. By enabling microservices deployment in containers, Docker simplifies the management of microservices and increases the efficiency of software development processes.

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