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Top 20 Docker Container Interview Questions Answers for Developers and DevOps

Hello guys, if you are preparing for DevOps Engineer interview or a Software developer job interviews like Java developer then preparing about Docker is a good idea. Docker has become an essential tool for packaging and deploying Software, particularly Microservices, and you can expect a couple of questions about Docker during Interview to check your knowledge. Having absolutely no idea of Docker before going into interview can be detrimental to your prospect considering the importance of container on deploying apps and services on Cloud. That's why I always programmers and developers to prepare Docker interview questions and revise key Docker concepts before interview. 

If you are wondering where you can find Docker interview questions then don't worry, in this article, I have shared common Docker related questions you can prepare for interviews. They are also great to revise key Docker concepts before interviews and they cover essential areas. 

If you don't know what is Docker then let me give you a brief overview. Docker was first introduced in 2013 and has since taken the IT world by storm. It has become a big hit with customers and as of 2018, it has more than 9 billion container image downloads. 

What this means for job hunters like you is that there is an ever-growing demand for software developers skilled in Docker. Docker streamlined the development and deployment of Software application as you can deploy both C++ and Java Microservice in same way as Docker image and Kubernetes can also scale them without worrying whether they are Java or C++ application. 

This article will teach you everything you need to know about Docker. The article is made up of the 20 most important Docker interview questions. Using this article, you will be able to ace your interview, impress your potential employers, and land your dream job.




Top 20 Docker Questions with Answers for 1 to 3 Years Experienced Developers and DevOps

This article covers some of the most frequently asked interview questions related to Docker. The questions cover basic concepts like containerization, virtualization, and hypervisor, as well as advanced topics like Code Pipeline Management and Application Isolation. 

For easy access, I have divided this article into 3 sections. The first section includes Basic Docker Questions relating to concepts like virtualization, hypervisor, and containerization.

The second section takes it up a notch and introduces you to some Advanced Docker Questions. You will learn about things like Code Pipeline Management, Developer Productivity, and Application Isolation. 

The third and final section will teach you about some Basic Docker Commands. Since most of the interviewer looks for hands-on Docker skills its important to remember and practice essential Docker commands. In this section You will learn how to start, stop, and kill a container, as well as list all the running containers.

1. Basic Docker Questions

Docker is basically an open-source containerization platform. What this means is that it helps developers to divide applications into different containers. 

1. What is Docker?

Since this will be an obvious question, we will start with a small definition. Docker is a containerization platform that you can use to package your applications and their dependencies together in the form of a container. This will help ensure that your application works smoothly in any environment. 

2. What is a Docker Container?

Docker containers are made up of the applications and all of their dependencies. In simple words, Docker containers are runtime instances of Docker images. They run on any computer, on any infrastructure, or on any cloud. 


3. What is Containerization?

In software development, it is common that code developed on one machine may not work on another machine. This is because of something called dependencies. The concept of containerization was developed to solve this problem. What this means is that an application is effectively bundled together with all of its configuration files and dependencies. Docker is one of the most famous containerization platforms. 



4. What is Hypervisor?

A hypervisor is a piece of software that makes the process of virtualization possible. Another name for a hypervisor is Virtual Machine Monitor. It is responsible for dividing the system and allocating resources to each divided environment. What this basically means is that you can have multiple OS on a single system. 

5. What is virtualization?

The process of creating the virtual version of something is known as virtualization. This can be computer storage, servers, or applications. Virtualization allows developers to divide one system into many different sections. Each of these sections can act as a single system. A software called a hypervisor makes this possible. 

6. What are Docker Images?

A Docker image can be called the source of a Docker container. What this means is that Docker images are used to create Docker Containers. When a developer runs a Docker image, an instance of a Docker Container is created. 

Docker interview questions with Answers


7. What is Docker Hub?

Docker Hub is kind of a registry where all the Docker Images are placed. Developers can select images from Docker Hub and use them to create containers or other images. Docker Hub is the world's largest registry of image containers. 



2. Advanced Docker Questions with Answers

Interviewers will ask questions from this section to check your experience of working with Docker. Once your interviewer realizes that you are familiar with the basic concepts of Docker, they will move on to some more advanced questions. This section of the article will help you understand some advanced Docker concepts. 

8. How is Docker different from other containerization methods?

Even though Docker is by far the most famous and efficient containerization method in the world, it is not the only one. What sets Docker apart is that Docker containers are easy to deploy in any cloud platform. This means that you can run more applications on the same hardware. It is also easier to quickly create containerized applications. The process of managing and deploying applications is also more efficient. You will also be able to share containers with your applications. 

9. How far do Docker Containers scale? What are the requirements?

Most of what you see on the internet, including websites like Google and Twitter, runs on container technology.
What this means is that containers can be scaled to such a degree that you can have thousands or even millions of containers running in parallel.
As regards requirements, you will need to have enough memory and other OS requirements to make sure that containers are effectively scaled.


Docker questions from Interviews



10. What platforms does Docker run on?

Docker runs on a multitude of platforms. You should make sure that you mention the platform that the company you are interviewing for uses in your answer. 
Docker can be used in cloud platforms like Amazon ECS, Amazon EC2, Microsoft Azure, Google Compute Engine, and Rackspace. 
It also runs on Ubuntu, ArchLinux, OpenSUSE, CRUX, Fedora, RHEL, and Gentoo. 

11. How do you identify the status of a Docker Container?

There are six states that a Docker Container can have - Created, Running, Paused, Restarting, Exited, and Dead. 
You can use a command like '$ docker ps' to check the current state of a container. 
You also need to understand that you cannot remove a paused container from Docker. The container should first be stopped before it can be removed.
It is also not possible for a container to restart by itself. 

12. How many Containers can run per host?

The cool thing here is that you can run as many containers as you want. There are no restrictions on Docker. But you should note that every container needs storage space, memory, and CPU. So you should make sure that you have the necessary hardware before running a container. You will also need to consider the size of the application. Containers are mostly lightweight but it depends a lot on the host OS.

13. Will Cloud overtake the use of Containerization?

Docker containers are gaining popularity. Cloud platforms are also on the rise. As you are interviewing for a Docker position, you should say that Docker will never be replaced by Cloud. You should also be able to back up your opinion.

Companies should take into consideration all of their requirements before deciding whether to go with Docker or Cloud. Most companies these days have integrated Docker with Cloud. This will make it possible to get the best of both worlds. 

Docker questions and answers for interviews



14. How will you monitor Docker in production?

There are many ways to monitor Docker in production. Docker provides many functionalities like Docker stats and Docker vents to do the same. 
Docker stats will give you the CPU and memory usage of an application. You can use Docker events to gain information about the different activities taking place in Docker. 


3. Basic Docker Commands Interview Questions

Once your interviewer realizes that you have a strong theoretical understanding of Docker, they will increase the difficulty to test your practical experience. This section of the article will teach you about some of the basic Docker commands. You can use your knowledge of Docker commands to impress your interviewer. 

14. How do you find out the number of running, paused, and stopped Containers?

You can use the following command to check the number of containers running, paused, and stopped. 

$ docker info

15. How do you login into the Docker repository?

You can use the following command to login into the Docker Hub.

$ docker login

After typing this command, you will be required to enter your username and password.

16. How can you make modifications to a base image and customize it?

First, you will need to pull an image from the Docker Hub into your local system. You can use the following command to pull an image.

$ docker pull <image_name>

17. How do you use an image to create a Docker container?

You can pull an image from the Docker hub using the command given above and then run it to create a container. You can use the following command.

$ docker run-it-d <image_name>

The '-d' in the command means that the container needs to start in detached mode.

Docker interview questions with answers



18. What is the command for listing all the running containers?

You can use the following command for listing all the running containers.

$ docker ps

19. What is the command to start, stop, and kill a container?

You can use the following command to start a Docker container.

$ docker start <container_id>

The following command can be used to stop running a container.

$ docker stop <container_id>

You can kill a container with the following command.

$ docker kill <container_id>

20. How do you edit and update a container? You should also make it a new container and store it on the local system.

This may sound really complicated but you can perform all of these actions with the help of a single command. 

$ docker commit <container_id> <username/image_name>




Bonus Docker Interview Questions

1. What is a DockerFile?

A DockerFile is basically a text file that is made up of all the commands which need to be run for building a Docker image. 

2. What can you tell us about the functionality of a hypervisor?

A hypervisor is actually a piece of software that makes the process of virtualization happen. Because of this, it is also sometimes referred to as the Virtual Machine Monitor. A hypervisor can also divide the resources between host system and allocate these guest environments to all of the guest environments. 
There are 2 types of hypervisor.
Native Hypervisor, which is also known as Bare-metal hypervisor, runs directly on the underlying host system. This ensures there is direct access to the host hardware and does not require base OS.
In contrast, Host Sypervisor makes use of the underlying host operating system where the existing OS is installed.

3. What can you tell us about Docker Compose?

Docker Compose is basically a YAML file that is made up of all the details related to the various services, volumes, and networks that are all required for setting up a Docker-based application. It can be used for creating multiple Docker containers as well as establish the necessary communication between them. 


That's all about the frequently asked Docker interview questions with answers. I have no doubt that the questions in this article will help you land a dream software job. 

Docker is a very fundamental part of cloud computing and it is essential for every software developer to be knowledgeable about Docker. This is because containerized applications can run on a wide variety of environments like different operating systems, cloud platforms, and infrastructures. 

Docker is basically a virtualization technology that you can use to package applications into containers. The questions in this article will not only help you to land a dream job but make you more productive in your current one. Docker containers include all the dependencies of an application like frameworks and libraries so that you can run your application in an efficient manner. 

I thank you for finishing this article. You are well on your way to mastering Docker and landing your dream job. If you liked this list of Top 20 Docker Questions with Answers, feel free to share it with your friends and family. If you have any doubts about Docker, you can also drop a comment and we will respond as soon as possible. 



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