40+ Best Microservices Interview Questions To Get Hired With

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The use of microservices is gaining in popularity when you think about advanced technology-driven products and services. As the need for uptime and advanced features continues to expand, engineers are relying more on microservices. In a nutshell, microservices allows engineers to think about specific features and functionality for a set scope of code, all of which other engineers can work on, improve and deploy. Meanwhile, not affecting other parts of the product or feature set which might be being used at that very time. It gives some degree of clarity to the engineering and also allows teams to address one specific part of their product for which they want to improve at that moment or in their agile planning. Usually, microservices allow code to be very lightweight. They are a series of features all working for each other, doing specific tasks. This means that code can be significantly less lines because it is really only trying to solve one part of the equation versus trying to ensure all parts of the connectivity of the application are occurring. Below are the best microservices interview questions and answers I could think of. As you go through these questions, please know that these are mock questions for advanced microservices engineers. If you are applying for a distributed systems position, these interview questions will still apply to you. I would brush yourself up on microservices before applying for a distributed systems position. For the most part, these metholodigies are very similar. That is specifically, microservices and distributed systems. You should always try to answer interview questions with your own words. Spend time with a friend to go through them and attempt to find your own confident answers to each question. Then, you'll be prepared for your next technical job interview! Good luck.

1. What are microservices?

Microservices or microservices architecture is an architectural style that is used in the software development of large systems. It builds the application as a group of independent services around a business domain. To understand this, you need to think about bees and how they make their honeycombs. Bees build combs by arranging hexagonal wax cells; they begin with a small part using gathered materials and build up into the large beehives that we harvest honey from. The systematic arrangement of these cells creates a definite pattern which in turn makes a strong foundation which holds the hive together and prevents it from collapsing. The theory behind this is that each wax cell is independent of the other yet is also related to the other independent cells. This is an ingenious structure because it means that when one cell is damaged the other cells remain perfectly fine; that way, the bees can repair the damaged cells without having to tear down to the entire beehive.

Microservices is, therefore, an architectural plan that contains many small services where a single microservice is restricted to one business application. Together, these microservices form a more complex application that meets the business needs as a whole. We can take the example of an online shop; it has separate microservices for different parts such as order-processing, shopping carts, user-accounts, and order processing. These are parts that are essential for an extensive online shopping website, and thanks to the microstructure, when one piece is not working the rest will still function as normal which makes it easier for employees to fix without having to take down the entire website. Therefore, if the product-catalog is not working, you can still track your order.

2. What is the difference between microservices and monolith (SOA) structures?

A monolith is like the direct opposite of the microservices structure; all the elements are dependent of each other and so if one fails all of them fail. Below is a diagram of the monolith structure using the example of an online shop.

As you can see, all the collaborating elements combine into one application. Unfortunately, such a structure is not as sturdy because if one part of the shop fails, then all of it fails and it would have to be temporarily shut down to fix the part. This is not the case with a microservice structure; the online shop can be fixed without having to shut down the site.

3. What are the critical differences between SOA and microservices Architecture?

• SOA follows the “share-as-much-as-possible” architecture approach while microservices Follows “share-as-little-as-possible” architecture approach.
• In SOA, the focus is on business functionality reuse while in microservices, the importance is on the concept of bounded context.
• In SOA, any systematic change would require changing the monolith while in microservices, a systematic difference is to create a new service.
• In SOA, delivery has become popular, but it is not yet mainstream while in microservices, there is continuous delivery.
• In SOA, Traditional Relational Databases are used often while in microservices, the frequently used are Modern Relational Databases.
• In SOA, they have common or regular standards and governance while microservices strives to focus on the collaboration of people and freedom of other options.
• SOA is entirely focused on maximizing the application service reusability while microservices is more on decoupling above other things.
• SOA supports multiple message protocols while microservices can only support lightweight protocols such as RESET.
• SOA is multithreaded and has more overheads to handle I/O while microservices are single-threaded with the use of Event Loop Features.

4. What are the elements of microservices?

• Decoupling- the services within a given system are highly decoupled meaning that the application as an entity can be built, scaled, and altered easily without affecting other services.
• Componentization- microservices, as we have established, are treated as independent elements so they can be replaced and upgraded individually.
• Capabilities- microservices are simple because they focus on one ability each.
• Delivery- microservices allow the regular releases of software through a planned automatic creation of software, testing, and approval.
• Autonomy- developers and teams can build independently off of each other meaning that the process is done quickly.
• Responsibility- microservices are personal; they choose to treat applications as products that they are responsible for rather than projects.
• Decentralized Governance- when working with microservices the aim is to focus on the right tool for the right job. This means that there is no technological or standardized pattern; developers are therefore free to choose the best tools to solve their problems.
• Agility- microservices work in support of agile development which allows new features to be developed and discarded quickly and easily.

5. How do microservices work?

The architecture of a microservice has components as follows:

• Clients- clients are users from different platforms using different devices to send requests.
• Identity Providers- the providers, are the ones who authenticate the clients’ identities and issue out security tokens.
• API Gateway- this is where client requests are handled.
• Static Content- this is home to all the content of the system.
• Management- this balances services on nodes and identifies any failures in the system.
• Service Discovery- this is a guide to find the roadmap of the communication between microservices.
• Content Delivery Networks- this is the distributed network of proxy servers and their data centers.
• Remote Service- this service enables the remote access information that resides on a network of IT devices.

6. What is the spring cloud?

Spring cloud is the building blocks of microservice structures and Cloud. It is the infrastructure provider of microservices like provide use services such as Service Discovery, a Configuration server, and Monitoring. Spring could also offer many other open source projects such as Netflix. Spring cloud uses Spring Boot style starters; many use-cases are supported by it including Cloud Integration, Dynamic Reconfiguration, Service Discovery, Security, and Client-side Load Balancing just to mention a few.

@EnableEurekaServer is the annotation that allows people to register microservices to the spring cloud while the @EnableDiscoveryClient annotation is the gateway for clients to query Discovery server to find microservices.

7. What problems are solved by Spring Cloud?

Developing distributed microservices using spring cloud solves some problems such as:

• Reduces performance issues- using spring cloud allows the use of various operational overheads which in turn reduces performance issues.
• Complexity linked with distributed systems- this is inclusive of network issues, Latency overhead, Bandwidth issues, and also security issues.
• Load balancing- spring cloud improves the sharing of workload among different computing resources such as network links, central processing units, and computing resources.
• Ability to handle Service Discovery- service discovery allows processes and services in a cluster to find each other and communicate. • Solved redundancy issues- these are common in distributed systems.

8. What is the spring boot?

This is a ready production-grade framework that is currently being developed and kept by Pivotal Inc. as a Spring-based application. It is used to create applications that stand alone, and the servers will be inside the runtime dependency libraries in embedded servers because they will be inserted. Management of the data source connections will be easier because it will use single configuration files that can connect to any type of database with ease. This can be made possible with the use of the started project by using Project Build tools such as Maven or Gradle.

9. What are Containers and why they are used in microservices?

Containers are defined in microservice terms as the packaging of all the components that are required into a single package to make it independent of all other parts or operating systems by virtualizing its runtime environment. Containers are used with microservices because they help to make them loosely coupled and readily available; they make the microservices also easy to deploy and maintain. A container helps the application to speed up in a short time; the Windows Container contains Hyper-V container which functions in such a way that the host container is not linked or shared with the Hyper-V containers.

10. What is Docker and how it is used along with microservices?

Docker which is also known as the process of containerization that makes the process of operating system level as virtualization. It is a computer program that is used to package and run the containers. After the containers are packaged, they will sit on top of the Docker; afterward, all the containers will run via a single OS kernel. The result of this is lightweight than the existing virtual machine level operating system processes. The Docker contains a daemon that is the manager of containers in the Docker. Docker has high-level APIs (Application Programming Interfaces) for exposing lightweight APIs to be used will be able to run the isolated processes.

11. What are the usecases of Docker?

There are many different applications of Docker including:

• It allows easier and simpler configuration.
• It offers productive and practical techniques of development.
• It has the advantage of continuous monitoring.
• It ensures that there are continuous development and deployment.
• It offers the development of rapid application.
• It has consolidated server features.
• It is easy to manage.

12. What are different types of tests for microservices?

When you are working with microservices, testing is inevitable and complex because there are many microservices working together. As such, they need to be tested on different levels; three different levels to be precise. They are as follows:

• Bottom level- here there are technology0facing tests such as performance tests and unit tests. These tests are fully and easily automated.
• Middle level- on this level there are tests for exploratory testing such as usability tests and stress tests.
• Top level- on the highest level is the acceptance tests which are fewer in number as compared to the other two levels. The acceptant tests help the stockholders to understand and verify software features.

13. What are some of the advantages of microservices?

There are several significant advantages of microservices such as:

• It allows you the freedom to use different technologies instead of limiting you to just one or two. This is because microservices can easily mix with other databases and libraries with ease.
• Because each microservice focuses on a single capability, should it fail, it will not bring down the whole system. The microservice will be fixed without interrupting the others.
• microservices has a smaller code base which makes it easy to maintain.
• It provides better support for s smaller parallel team.
• It is easy to scale as an individual component.
• As we have established it also supports individual deployable units.
• It encourages regular software releases.
• It ensures the security of each service.
• Through it, several services can be developed parallel to each other and deployed as such.
• It reduces the time used for deployment.
• They are scalable and reliable.
• They are more flexible and easy to develop within a shorter time frame.
• It offers secure code and applications.

14. What are the disadvantages of microservices?

Microservices however great is not perfect. They are subject to flaws as listed below:

• Unfortunately, the use of microservices increases troubleshooting challenges.
• It also becomes tough to achieve a stiff consistency across services.
• ACID transactions do not span multiple processes.
• Due to remote calls, there is an increase in delay.
• In turn, there is also an increased effort for configuration and other necessary operations.
• It becomes challenging to manage transaction safety; this is a crippling disadvantage.
• Moreover, it becomes challenging to track data across different boundaries.
• It is also hard to code between services.

15. What are the challenges faced while using microservices?

Using microservices has its challenges just like using monolith and SAO. The problems you will come across include:

• Using this type of architecture means that you need to ready for operations overhead.
• Also, for heterogeneously distributed microservices you will require the help of professionals to support it.
• It is a heavily involved model because its features are distributed.
• There is always a big need for an end to end testing.
• A distributed system makes it hard to debug and trace the issues.
• Required cultural changes in across teams like Dev and Ops working together even in the same team.

16. What are client Certificates?

These are digital certificates, which are utilized by the client systems for making authenticated requests to a remote server, which is referred to as the client certificate. These play a significant role when it comes to mutual authentication designs and they give strong assurance to the identity of the requester.

17. What is the use of PACT when it comes to microservices architecture?

PACT refers to an open source tool, which allows for testing interactions between the service providers and clients in isolation against the contract made so the microservices integration may increase in its levels of reliability.

Use in microservices:
• It can be used to test the consumer driven contracts between the consumer and a provider of a microservice.
• It may also be used to implement consumer Driven Contract within microservices.

18. What is OAuth?

OAuth means open authorization protocol. This would allow for the access of resources for the resource owner through providing client applications on the HTTP services such as the third party providers, GitHub and Facebook. With this, it is then possible to share the resources stored on one site with another site without having to utilize their credentials.

19. What is Conway’s Law?

It states that an organization, which designs a system may produce a design whose structure is a copy of communication structure of the firm. The regulation conveys the fact in order for the software module to adequately function, the complete team needs to be in communication as well. That means the structure of the system is reflective of the social boundaries of the organization, which came up with it.

20. What is Contract Testing?

A contract test according to Martin Flower is a test at the boundary of the external service that verifies if it meets the contract as expected by the consuming service. A contract test also does not test on the behavior of the service in depth. It tests the inputs and outputs of the service calls within the required attributes and the response latency, which throughout is within the allowed limits.

21. What is known as end-to-end microservices Testing?

End-to-end testing validates each process within the workflow as to whether it is functioning in the right manner. This makes certain the system works together as a whole and thus satisfies all of the requirements. You might say that end to end testing is a test where everything is tested after a particular period.

22. What is the meaning of semantic monitoring within microservices architecture?

Semantic monitoring combines the automated tests with monitoring of the application. It also allows one to find the reasons why the business is not attaining more profits than before.

23. What is a CDC?

The CDC is a consumer driven contract. It is a pattern for the developing microservices such that the external systems may utilize them.

24. What are some of the Reactive Extensions in microservices?

The Reactive Extensions also known as Rx. This is a design pattern, which allows for the collection of results by calling different services and then compiling a combined type of response. Rx is a great tool within distributed systems that works in an exact manner opposite the legacy flows.

25. What is the term ‘Continuous Monitoring’?

Continuous monitoring is one of the means used for searching compliance and risk issues linked with the operational and financial environment. It contains the processes and the working systems that support some of the efficient and actual operations.

26. How is it possible to monitor several microservices for different indicators such as Health?

Spring Boost gives actuator end points to monitor the different metrics for the individual microservices. These endpoints become significant towards getting information concerning applications such as if they are up and if their components like database are working in the appropriate manner. One of the difficulties though concerning actuator end points is there would be a need to individually hit the end points for the applications in order to know their health or status. Imagine microservices entailing 50 applications so the admin would have to hit the actuator end-points for all of the 50 applications. To deal with this, there will be an open source project, which is located at Built on top of Spring Boot Actuator. It provides a web UI in order to allow for the visualization of metrics of different applications.

27. What does service registration and discovery mean? How is it implemented when it comes to spring cloud?

When you start a project, there are probably configurations in the properties file available. As more of the services are developed and deployed, the adding and modification of these properties gets more and more complex. There are services, which may go down, and others may change. this manual changing of the properties may also lead to issues. In this case, Eureka Service Registration and Discovery assists in these scenarios. As the services are registered to the Eureka serer and lookup done by calling the Eureka Server, any of the changes within the service stations does not need to be handled and is taken care of.

28. What does it take to achieve Server side load balancing with the use of Spring Cloud?

Server side load balancing may be achieved using Netflix Zuul. Zuul in this case is a JVM based router and server side load balancing by Netflix. It gives single entry to the system that allows the browser, mobile application or other user interfaces to consume the services from different hosts without having to manage cross origin resource sharing or (CORS) and the authentication for one. It is possible to integrate Zuul with some of the other Netflix projects such as Hystric for the purposes of fault tolerance and Eureka for self-discovery or utilize it in order to manage routing the rules, filters and the load balancing across the system.

29. What is Eureka?

Eureka refers to a Netflix Service Discovery Server and Client. Eureka Server utilizes Spring Cloud.

30. How do independent microservices communicate with one another?

This is dependent on the needs of your project. Though a lot of the time, the developers may utilize HTTP/ REST with JSON or Binary protocol. On the other hand, they can utilize any of the communication protocols to do so.

31. What is DRY in microservices architecture?

DRY stands for ‘Don’t Repeat Yourself’. It promotes the concept of reusing the code. This can result in the development and sharing of libraries, which would then result in tight coupling.

32. What is a consumer driven contract (CDC)?

This is a pattern for the development of microservices such that they would be utilized by external systems. When you work on microservices, there is a provider building it and there are some consumers, who use the microservice. Usually the providers may specify on the interfaces within an XML document. Though in Consumer Driven Contract, each of the consumer of service conveys the interface as expected from the Provider.

33. What is the role of the web, Restful APIs when it comes to microservices?

A microservice architecture is based according to a concept where all of the services would be able to interact with each other in order to build the business functionality. To achieve this, each of the microservice has to have an interface. That would make the web API important as an enable for the microservices. Being based according to the open network settings of the web, RESTful APIs would be the most logical model for the construction of interfaces between the different components within the microservice architecture.

34. Is it possible to create state machines out of microservices?

Each microservice owning its database is an independent and deployable program unit. This allows for the creation of a state machine in the process. It is possible to specify the different states and events for a particular microservice. We can define an order microservice. An order may have different states. The transitions of the order states then can be independent events within the order microservice.

35. What is the role of the architect when it comes to microservice Architecture?

The architect within microservices does the following:

• They assist in deciding the zoning of the components. In so doing they make certain the components are mutually cohesive though they should not be tightly coupled.
• They decide the broad outlines on the layout of the overall software system.
• They code with developers and learn challenges which are faced in everyday life.
• They make recommendations for particular tools and technologies to the team, which develops the microservices.
• They give technical governance so the teams within their development would follow the microservice principles.

36. What is Canary releasing?

This is an approach to reduce the risk of introducing new software versions within the process of production. This is done through slowly rolling out changes to small subsets of users before it is given out to the infrastructure thus making it available to every individual.

37. What is meant by continuous integration?

Continuous integration refers to the process of automating the build and testing the code each time a team member commits changes to the version control. That would encourage the developers so they can share code and the unit tests through merging the changes into a shared version control repository after every minute task completion.

38. What is the difference between Stub and Mock?

• Provides fixed behavior under the right conditions, which can be hard coded.
• A dummy object which assists in running the test.
• Any other behavior of the stub is never tested.

In an example, for an empty stack it is possible to create a stub which just returns true for empty () method. It does not care whether there is an element within the stack or not.

• This is a dummy object in which particular properties are initially set.
• The behavior of this object would be dependent on the set properties.
• The behavior of the object may also be tested.

For example, for the customer object it is possible to mock it by setting name and age. You can set the age as 12 and then test for isAdult() method which will either return true for the age that is greater than 18. The Mock Customer object would work for specified conditions.

39. What Netflix projects can you use?

Eureka by Netflix. It is the Netflix Service Discovery Server and Client. Netflix Ribbon. It gives different algorithms for client-side load balancing. Spring provides smart RestTemplate for service discovery and load balancing through the use of @loadbalanced annotation with RestTemplate instance.

40. How do you setup Service Discovery?

Spring Cloud support allows a number of ways to implement service discovery. The most popular though entails the use of Eureka. Spring Cloud would provide several annotation to make it easy to use and hide the majority of the complexities.

41. How does one eliminate non-determinism in tests?

The non-deterministic tests are those, which are not reliable. So it could happen that they pass and sometimes they may fail. When they fail as well, they are made to rerun in order to pass. The following are some of the means by which to remove non-determinism within tests:

• Isolation
• Time
• Resource leaks
• Remote
• Asynchronous
• Quarantine

42. What is Bounded Context?

Bounded context refers to a central pattern within Domain driven design. It is the focus of the DDD strategic design section, which concerns dealing with large models and teams. DDD handles the large models through dividing them into bounded contexts and being explicit concerning their interrelationships.

43. What is two-factor authentication?

Two-factor authentication allows for two levels of verification to an account during a login process.


If you are still feeling underprepared to interview at a technology company that is utilizing distributed systems or microservices, there are a few ways to get a little more prepared. In particular, you can try to replicate an application that already exists, using microservices. Consider this an experimental project of yours that you can showcase during your interview. Usually, during your interview, you'll have the opportunity to share some previous work experience. And having that project is one way to make sure your future employer knows you are a fit for the position. It can be harder to come up with a new application idea and try to build towards that. So usually what I recommend is replicating something that's easy to understand and that the person interviewing you may already have used. Enthusiasm, confidence and the ability to go above and beyond is the way to truly set yourself up for success in your interview session.

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