Top 20 Docker Interview Questions Answers Java Developers and DevOps

Hello guys, if you are preparing for a Java developer interview, a DevOps engineer interview or any software developer interview, one tool which should pay most attention is Docker. It's a container tool which allows you to package and deploy your application in cloud. Docker has many benefits as it not only standardized packaging and deployment but works nicely with Kubernetes which takes the scalability and automatic restart of your application. These are just a couple of benefits but because of all these, Docker has become an essential tool for every programmer and developer and that's why they are also quite important for interviews. 

If you are looking for Docker interview questions then you have come to the right place. Earlier, I have shared DevOps interview questions and Kubernetes interview questions and in this article, I am going to share common Docker interview questions with answers.

If you have used Docker in your work or just for fun you can most likely answer all of these Docker related questions but if you struggle to answer them then I suggest you to check out these best DevOps online courses to learn and revise essential Docker concepts and commands before interview. 

20 Docker Interview Questions with Answers for 1 to 2 years experienced

If you are worried about your Docker interview that is waiting for you, worry no more because you are going to find what will help you to be outstanding when compared with the rest of the candidates on the interview day. 

This article is giving you the chance of understanding the top 20 Docker interview questions with answers that you will likely face in your interview. The questions are as follows:

1. What is Docker?
Answer: Docker is an open-source containerization platform. It is used to automate the deployment of any application, using lightweight, portable containers.

Top 20 Docker Interview Questions With Answers

2. What are the important features of Docker?
Answer: The essential features of Docker are as follows:

  • Easy Modeling
  • Version control
  • Placement/Affinity
  • Application Agility
  • Developer Productivity
  • Operational Efficiencies

3. What are the states of the Docker container?
Answer: The important states of Docker container are:

  • Running
  • Paused
  • Restarting
  • Exited

4. What is the lifecycle of a Docker Container?
Answer: Docker containers have the following lifecycle:

  • Create a container
  • Run the container
  • Pause the container(optional)
  • Un-pause the container(optional)
  • Start the container
  • Stop the container
  • Restart the container
  • Kill the container
  • Destroy the container

5. What is Docker Hub?
Answer: Docker hub is a cloud-based registry that helps you to link code repositories. It allows you to build, test, and store your image in the Docker cloud. You can also deploy the image to your host with the help of the Docker hub.

6. What are the main drawbacks of Docker?

  • Doesn’t provide a storage option
  • Offer a poor monitoring option.
  • No automatic rescheduling of inactive Nodes
  • Complicated automatic horizontal scaling setup

7. What is memory-swap flag?
Answer: Memory-swap is a modified flag that only has meaning if- memory is also set. Swap allows the container to write express memory requirements to disk when the container has exhausted all the RAM which is available to it.

8. What is Hypervisor?
Answer: The hypervisor allows you to create a virtual environment in which the guest virtual machines operate. It controls the guest systems and checks if the resources are allocated to the guests as necessary.

9. Does Docker offer support for IPV6?
Answer: Yes, Docker provides support IPv6. IPv6 networking is supported only on Docker daemons runs on Linux hosts. However, if you want to enable IPv6 support in the Docker daemon, you need to modify /etc/docker/daemon.json and set the ipv6 key to true.

10. What is CNM?
Answer: CNM stands for Container Networking Model. It is a standard or specification from Docker, Inc. that forms the basis of container networking in a Docker environment. This docker’s approach provides container networking with support for multiple network drivers.

11. How many containers can run per host?
Answer: Depending on the environment where Docker is going to host the containers, there can be as many containers as the environment supports. The application size, and available resources (like CPU, and memory) will decide on the number of containers that can run on an environment. Though containers create newer CPUs on their own they can definitely provide efficient ways of utilizing the resources. The containers themselves are super lightweight and only last as long as the process they are running.

12. Is there a way to identify the status of a Docker container?
Answer: We can identify the status of a Docker container by running the command ‘docker ps –a’, which will in turn list down all the available docker containers with their corresponding statuses on the host. From there we can easily identify the container of interest to check its status correspondingly.

13. Do I lose my data when the Docker container exits?
Answer: There is no loss of data when any of your Docker containers exits as any of the data that your application writes to the disk in order to preserve it. This will be done until the container is explicitly deleted. The file system for the Docker container persists even after the Docker container is halted.

14. What is virtualization?
Answer: Virtualization is the process of creating a software-based, virtual version of something (compute storage, servers, application, etc.). These virtual versions or environments are created from a single physical hardware system. 

Virtualization lets you split one system into many different sections which act like separate, distinct individual systems. A software called Hypervisor makes this kind of splitting possible. The virtual environment created by the hypervisor is called Virtual Machine.

15. What are the three Docker components?

  • Docker Client: This component executes build and run operations to communicate with the Docker Host.
  • Docker Host: This component holds the Docker Daemon, Docker images, and Docker containers. The daemon sets up a connection to the Docker Registry.
  • Docker Registry: This component stores Docker images. It can be a public registry, such as Docker Hub or Docker Cloud, or a private registry.

16. What are the types of Hypevisors?
Answer: there are two types of hypevisors namely:

  • Native: Native hypervisors, or bare-metal hypervisors, run directly on the underlying host system. It gives us direct access to the hardware of the host system and doesn’t require a base server operating system.
  • Hosted: Hosted hypervisors use the underlying host operating system.

17. What is Docker Compose?
Answer: Docker Compose is a YAML file which contains details about the services, networks, and volumes for setting up the Docker application. So, you can use Docker Compose to create separate containers, host them and get them to communicate with each other. Each container will expose a port for communicating with other containers.

18. What is Docker Swarm?
Answer: Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, virtual Docker host. Docker Swarm serves the standard Docker API, any tool that already communicates with a Docker daemon can use Swarm to transparently scale to multiple hosts.

19. How will you monitor Docker in production?
Answer: Docker provides functionalities like docker stats and docker events to monitor docker in production. Docker stats provides CPU and memory usage of the container. Docker events provide information about the activities taking place in the docker daemon.

20. Can a container restart by itself?
Answer: No, it’s not possible for a container to restart by itself. By default the flag -restart is set to false.

That's all about frequently asked Docker interview questions for Programmers. Hope you have taken note of all the questions with answers listed above. They are going to form the basis of your transition to the next level as far as passing your interview is concerned. Keep going through the questions over and over until you are sure you have grasped everything.

If you think a particular topic is missing or you want to see more questions from any other Docker topics feel free to suggest in comments and I will try to add them to make this article even better. 

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Thanks for reading this article so far. All the best for your Java Developer and DevOps interviews and if you have any questions which don't know answer or any doubt feel free to ask in comments. 

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