Top Docker Interview Questions And Answers 2021

By Aaradhya Kumar

Last updated on Oct 29 2020

Top Docker Interview Questions And Answers 2021

Top Docker Interview Questions And Answers in 2021 


Docker, which was kicked off in 2013, got a boom in the IT industry by the end of 2017. In 2017, there was an exponential rise in the downloading of container image rates. With an increase in demand, it increased its recruitments subsequently. The employment rate got a strike, and the new job openings brought scopes for a better career. To crack the job and work with Docker, you need to pass the interview. And to pass the Docker interview questions and answers is definitely not a game of words. To make you achieve your goal with ease, we have listed down a few important Docker Interview questions and answers. So, here are the top interview questions that will help you out.


The Docker interview questions consist of a good rational question pattern. Starting from basics to advanced questions, the interviewer will test your ability and caliber to pass this by gradually advancing the level of the Docker Interview Questions. Usually, the interviewer goes from the basic level of the questions and then move towards the advanced one. Here are the Docker Interview Questions –


Best Docker Interview Questions and Answers


  • What is Docker?

Answers. It is a tool of intermodal freight transfer port that uses ISO containers to pack applications and the dependencies together. It packs them in the form of containers and also ensures that your application is working effectively. The efficiency remains seamless in production or development or test or environment. The container covers software in a file system consisting of code, system tools, personalization, system library, run time, and other essentials that are required to run them. Along with that, it stores the capacity to wrap anything installed on the server.

Docker Interview Questions-  Part 1
  • List some important features of Docker.



  • It has amazing operational efficiency.
  • The best part is its easy modeling.
  • It has good developer productivity 
  • Affinity rate 


  • What is Docker Container?

Answers. One of the critical questions related to Docker. It’s an ISO container that is used to pack the applications with the dependency. Container covers software in a file system that contains tools, code, etc. this Container can work in any computer or environment, in any infrastructure, in any cloud. It shares computing with other containers. Then it runs under an isolated process. This is done on the host OS in the userspace. It is formed by units of images.


  • What are the states in which a Docker container is found to be?


  1. Running
  2. Paused
  3. Restarting 
  4. Existed


  • What is Docker image? 


Answers. The image is the building unit or source of the Docker container. These images can be brought into play in any Docker environment.


  • What is Docker hub?


The images compile to create a Docker container. The registry where images live is called a hub. It is one of the largest public storehouses of image containers. Users are able to pick images and create their own containers and customized images.


  • What do you mean by Hypervisor? 


Answers:  That is a regular one in Docker Interview questions when it comes to the Docker Interview. The hypervisor is software that enables Virtualization, and hence, it is also known as Virtual Machine Monitor. It allows the host system and then assigns its resources as required to each virtual segment. On a single host system, we can have multiple Operating Systems. 

Further, we have two kinds of Hypervisor 


  1.  Native Hypervisor 


  1. Hosted Hypervisor 


Native Hypervisor: This Hypervisor is also known as a Bare-metal Hypervisor. It works directly on the basal host system. So, it doesn’t need a base server OS.

Hosted Hypervisor: This Hypervisor computes the underlying host system. So, it is known as Hosted Hypervisor.


  • What do you mean by Virtualization?


Answers: This Question has great potential in the Docker Interview. The process of developing a software-based virtual environment such as servers, applications, etc. is called Virtualization. In Virtualization, these virtual versions are formed of one physical hardware system. By using a software called Hypervisor, one system is splitter into many different sections. After splitting, each section works distinctly. This is done through Virtualization. The virtual version formed using hypervisor is known as a Virtual Machine. 


  • What do you mean by containerization?


Answers: While developing software on one machine, there are possibilities of malfunction of the code developed in one computer. The code might not work properly, and then, to solve this problem, the containerization concept is used. An application that is developed and stuffed into a bundle with its configuration files and dependencies into a container. The container enabled will form a bug-free environment with any configurations and libraries bundled together. It is one of the best and famous containerization environment.


Docker Interview Questions can also include differences and comparisons. You need to answers \each of the questions wisely to shine in front of the interviewers.


  • List the differences between Virtualization and containerization.

Answers: This can be an assured question in your interview. You need to answers on point and impress the interviewers with your knowledge.

Containers give an environment to run the application where the complete user space is extremely dedicated to the application. Every container functions distinctly. Even if changes are made in the container, it will never have an impact on the host or other distinctive working containers running under the same host. 

While, during Virtualization, a software called Hypervisor provides a virtual machine entirely to the guest

Each virtual machine is a physical machine, while each container is a different application.

Containers are extraction of the application layer, while virtual machines are extraction of the hardware layer.


  • What is  Docker Architecture?


Answers. Docker Architecture has Docker Engine. It is a client-server application. This is one of the major questions that is regularly asked in the Interviews.


The major components of the Docker Engine are : 

  • The server that is a long-running program called a daemon process
  • REST API with coded programs that are used to interact with the daemon and instruct it what and when to do
  • CLI – Command Line Interface client
  • The Command Line Interface (CLI) uses Docker REST API to control and talk to Docker daemon by scripting, or direct Command Line Interface (CLI) commands. Many more Docker applications use REST API and CLI direct command.


  • What does CNM stand for?

Answers. CNM is the abbreviation for Container Networking Model. It is the basis of container networking in the Docker version. You can answers this kind of Questions, in a small a contained sentence.


  • What is Docker file?

Answers. It is known as the file that provides an introduction to Docker to form images by reading that information. This file is basically said to be a text document. It consists of all commands that a user would use on the command line to form an image. Users can create an automated build known as Docker build. This can execute different command-line instructions.

  • What do you mean by Docker compose?


Answers. A -compose is a YAML file. It consists of crude details about services, networks, etc. This is used to set up the applications. By using this compose, one can create a distinct container and host them to get them so that they can communicate with each other. Each container has a port. This port is used to communicate with other containers.


  • What is Docker Namespace?

Answers. In containers, the namespace adds an isolation layer. It is a Linux feature. To safeguard the underlying host system and make it portable, it provides many namespaces. PID, IPC, Mount, User, Network are the names of a few Namespace supported by Docker.


  • State the lifecycle of a Docker Container.


  1. Creation of a container 
  2. Running of the container 
  3. Pause the container 
  4. Un-pause the container. If paused
  5. Starting of the container
  6. Stopping the container 
  7. Restart the container 
  8. Kill the container 
  9. Finally, the destruction of the container 


  • What is Docker Machine?


Answers. A tool that enables the user to install Docker Engine is called its Machine. This installation is done on a virtual host. These virtual hosts can be managed using commands from the machine. This machine also allows the provision of Swarm Clusters.


  • What do you mean by the client?


Answers. Command-line interference tools are provided to the clients to interact with Daemon.


The interviewer will also test your knowledge regarding the commands. These are some important frequently asked Docker Interview Questions and answers.


  • How to check for Docker Client?

Answers. The command: $ docker version 

  • How to check for the Docker Server version?

Answers. We can check for Docker Server version from the command:

                                $ docker version 

  • How can you get the detailed number of containers that are running, paused, and stopped?

Answers. To get detailed information about the number of containers that are running paused and stopped from the Docker installed on your system, we need to use the command:

                               $ docker info

Using this command, you can get information about the number of containers, the number of images, and a lot more.

  • If you are unsure about the command and you wish to confirm it, then how will you get help on that particular command?

Answers. The following command will help you with the usage of a command, the syntax, etc.

                             $ Docker - -help 

The above command will help you list all the Docker commands

For wishing help regarding one specific command, you need to use the syntax;

                          $ docker - -help

  • How would you log in to the Docker repository?

Answers. To login into the Docker repository, I.e.,, use the command:

                           $ docker login

You will be prompted with your username and password.

Use them and get logged in.

  • If you would like to use a base image and make modifications or personalize it, how would you do that? 

Answers. The command to pull an image from Docker hub is :

                          $ docker pull

  • How can you create a Docker container from an image?

Answers: Step 1: Pull an image from the Docker repository with the command

                      $ docker pull

Run this command and run it to create a container 


        Step 2: Use the command 

                         $ docker run -it -d  

This command will enable to create of a Docker container from an image.


  • What do mean by -d in command in Docker


Answers. -d implies that the container has to start in detached mode.


  • How will you list all the running containers?


Answers. To list all the running containers, use the command : 

                    $ docker ps 


  • Just think that you got three containers running out of these, and you want to access one of them. How would you access a running container?


Answers. To access the running container, use the command 

          $ docker exec -it bash


  • What is exec used in a command?


Answers. The exec in command enables us to get inside a container and work with it.


  • How to start a container when you wish to?


Answers: To start a container, use the command 

             $ docker start


  • How to stop a container?


Answers: To stop a container, use the command 

              $ docker stop


  • How to kill a container?


Answers: To kill a container, use the command 

              $ docker kill  


  • Can you use a container? And then edit and update it? How can you make a new container and store it on the local system?


Answers: Yes, of course! We can use a container and edit it and update it as well with just one command

              $ docker commit <username/imagename> 


  • How would you push the image you have worked with to the hub?


Answers. To push the image that I have once worked with into the Docker hub, I will command:

               $ docker push <username/image_name> 


  • How can you delete a stopped container?


Answers. To delete a stopped container, I will give the command 

             $ docker rm


  • How can you delete an image from the local storage system?


Answers. To delete an image from the local storage system, I will give the command 

            $ docker rim  


  • How can you build a Dockerfile?


Answers. Step 1: Write a Docker file

Step 2: Build the Docker file to create an image with those specifications 

Step 3: To build a Docker file, use the command :

                 $ docker build


  • When can you use “ .dockerfile_name," and when do you use the entire path?


Answers. We use “.dockerfile_name" when the Dockerfile is present in the same directory, and we can use the entire path if the Dockerfile exists somewhere else.


  • Why the docker system prune is used?


Answers: The command is 

          $ docker system prune

This command is used to remove all the stopped containers. 

This command is very useful as it cleansers the system by deleting all the dangling images, catches, stopped containers, and unused networks.


Good hold on the commands will help you answer maximum Docker Interview Questions. 


  • Suppose a Docker container exists. Will you lose your data?


Answers. No. No data will be closed when the Docker container exists. Once your application writes to the container, it gets saved on the disk until you command to delete the container. Even after the container halts, the file system for the container persists.


  • Where is Docker being used?


Answers. It is being used in the following manner –


  1. Simplifying configuration 
  2. Code Pipeline Management 
  3. Developer Productivity 
  4. Application isolation 
  5. Debugging capabilities 
  6. Multi-tenancy
  • Rapid deployment 


The explanations of the above points are given below.


  • 1. It lets you simplify configuration into code in your environment and utilize it.


  • 2. Different systems are used for development as well as production. The code goes by a different zone, and different systems are used for it. For this reason, it maintains consistency in code Pipeline management


  • 3. Apps are isolated as applications are wrapped with all the configurations and dependencies into a container. So, any hardware that supports it can run those apps in it.


  • 4. It has many debugging tools. These tools are not just specific to containers. Still, those debugging tools work well with containers.


  • 5. It will eradicate the necessity to boost a complete operating system from scratch. This reduces deployment time.


  • State the difference between Docker and other containerization methods.


Answers. Docker containers can easily run in any cloud platform. It can contain more applications while working on the same hardware. It also makes it easy for the user to create quickly containerized applications that are ready to run. With the help of this, it is very easy to manage and deploy applications and share containers with the applications as well in comparison to other containerized systems.


  • What platforms do you know where Docker runs?


Answers. It runs on many Linux administration and cloud platforms.


  • CRUX 3.0


  • Gentoo


  • RHEL 6.5+


  • CentOS 6+


  • Fedora 19/20+


  • Amazon EC2


  • Amazon ECS


  • Google Compute Engine 


  • Rackspace 


  • Microsoft Azure 


( we would recommend you to do some more research regarding this as this question can be more tricky )


  • Tell us a way to identify the status of a Docker container.


Answers: The container can be at created or running or paused or restarting or exited or dead status.

To check the doctor state at any point, the command is –


                $ docker ps ( This command will help you list out all running containers )

To look for all containers, use the command 


                $ docker ps -a

  • Removal process explained: paused container from Docker?


Answers. (This is a very tricky question. Approach this with confidence)


We cannot remove a paused container from Docker. To remove a container, the container needs to be in the stopped state.


  • Can you say if a container can restart by itself?


Answers. No. A container cannot restart by itself.


  • According to you, what is the number of containers can run per host?


Answers. Docker doesn’t have any restrictions on the numbers of containers. So, there can be many containers to run per host as per your wish. But you need to consider the storage space, CPU, hardware memory, and application size because these are restricted.


  • Explain the monitor Docker’s production process?


Answers. Functionalities provided by Docker such as 

  • Docker stats
  • Docker events 


Helps to monitor Docker in production. They provide information about the events taking place in the Docker daemon.


  • State the default Docker network driver.


Answers. Network drivers such as, are provided by Docker and are by default. 


  • Is it a good idea to run Docker compose in Docker production?


Answers. Yes! It is a good idea to run Docker compose in production. It is the best practical application of Docker compose. E.g., CI, staging, testing, etc.


  • While moving your Docker compose file to the production, what changes do you expect?


Answers. Before moving my file, I need to make a few changes in the compose file.


  1. Volume bindings need to be removed so that the code doesn’t change with the change in its environment
  2. I will specify a restart policy
  3. I will add log aggregator alike extra services
  4. I need to bind to different ports present in the host system.


  • What do you know about load balancing across containers and host? Do you know its works?

Answers. When we use docker with multiple containers with different hosts, we need to balance the load of the coming traffic. To balance the load of the incoming traffic, Load balancing and HAproxy is used. In this case, if one container crashes, the other container will automatically start working. And hence, the traffic gets it’s the new route to the new container. 



With Proper planning, strategizing full of confidence will make you outshine in front of your interviewers. Let us help you clear this interview super easy. As the world's best mentor in IT Certifications we are feeling obliged to help our adherents to enroll in our DevOps course

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Have Practice well and have a good amount of research before during the preparatory period. These Docker interview questions will help you out.


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About the Author

Sprintzeal   Aaradhya Kumar

With years of experience and a vast amount of knowledge in Project Management, Agile Management, Scrum, and other popular domains, Aradhya Kumar is well-versed in creating content for audiences from various fields and industries.

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