Top Docker Interview Questions and Answers for 2020

by StarAgile

August 25, 2020
Category DevOps


Are you a developer looking for a job? Or Do you want to showcase your system admin skill in interview? Yes, these questions are for those who are hunting for a better prospect in DevOps skills. You need to understand about this tool which is of great help to both the developing team and the admin team. 

It is an open source platform as a service or PaaS based on Linux containers. It uses OS-level virtualization to deliver software in packages called containers. Containers are isolated and have their libraries, software, and own configuration files. The containers talk to each other with well-defined channels.

It is developed to create, deploy, and run applications on the containers. 

It helps the applications in the container to typically run on any OS or environment whether it is cloud or laptop or workstations.

It is a platform that runs every application separated and segregated in the kernel containerization feature. 

Yes, we are talking about Docker. It is written in the Go language and developed by Docker Inc.

Docker image is a set of files which has no state and Docker containers are runtime instance of the images.

The Docker architecture is shown in the image below


It is used for applications that are self-sufficient and isolated in the container and can run in any environment. Thus helps DevOps engineers with the continuous deployment feature that does not have to go back and forth with the development and operations activities. This helps the organization to save operational costs and overheads.

Docker interview questions about volume 

1. What is the use of Docker volume?

Volumes are the way to save data in Docker containers and services. These are the files and directories they exist as normal files and directories on the host systems that are outside of the default union file system. It can be used to share data between multiple containers.

2. What is the Docker volume command?

Docker volume command is used to manage the Docker volume and can be written on the Docker CLI commands or Docker API.

3. How do I run a Docker container with volume?

First, create a volume and then start the container. To mount a volume with the app of the container using "v" or "volume" or "mount" commands.

4. How can I see Docker volumes?

Volumes are stored in the host file system which is managed by Docker for example on Linux the locations are /var/lib/Docker/volumes

5. How do I share volume between containers?

Steps are as follows,

  • Create a container with data volume.
  • Create a new container and add the container to the data volume you have created in the first step.
  • Verify whether you can share data between the containers.

Docker interview questions and answers about command

1. What is Docker command?

Docker commands line is the command-line interface for writing Docker commands. Examples of Docker commands are built, run, etc

2. What is Run command in DockerFile?

Run lets you execute commands in your Docker image. It is used to install a package or create a directory inside the Docker image. These commands get executed once when the build time is executed and it gets written as the Docker image by making a new layer.

3. What is the difference between Run and CMD in Dockerfile?

CMD and RUN are both Dockerfile instructions. CMD is used for defining a default command to run when the container starts. Whereas RUN is used to execute commands inside of your Docker image.

4. Does CMD override entrypoint?

CMD and Entrypoint can be overridden by the command line flags. All these flags can be overridden by the developers when they do Docker run.

5. What is Docker images command?

A Docker image file consists of multiple layers that are used to execute code in a Docker container. An image is built from the instruction to a complete and executable version of an application. When the Docker runs an image it can become one or multiple instances of the container.

Top 5 Tricky Docker interview questions and answers for experienced

1. Is container technology new?

It is not new. Different variations of the containers technology were there in Unix or Linux for quite a long time. For example: - Linux OpenVZ, Solaris Zones which is a Solaris container, FreeBSD Jails, and AIX Workload Partitions aka WPAR's

2. State a couple of advantages of Docker?

It is a lightweight combined with workflow. It is easy to package and ship code. The code is portable with Docker and can run in any environment.

3. Difference between standard virtualization and Docker?

Docker is OS-level virtualization. Whereas the Virtual machines run on the physical hardware via an intermediate layer called the hypervisor.

4. Name a couple of Potential use of Docker?

It can be used in hyper scaling of the containers that is it can be a lot of containers on the host and they are very fast. Next is the dev, test, and build the pipeline that Docker can be used for.

5. Difference between Docker image and the container?

Docker image is the files that do not have the state, they are stateless. Whereas the Docker containers are instance of the image or the state of execution of the Docker image

Very basic Docker interview questions for freshers 

1. What are some areas of application of Docker?

  • Docker can be used in isolating the applications.
  • Docker encapsulates the applications
  • With Docker lot of isolated applications can be run in one platform that is the same OS.
  • It can be used to bundle applications and run in any environment.
  • It can be a DevOps tool for managing the dev, build test pipelines.
  • It can be used as a multi-tenancy feature.
  • It can be used for solving and simplifying the configurations issues
  • It has enhanced debugging capability

2. How does Docker differ from other containerization methods?

  • It is easy and versatile.
  • It can take a load of a large volume of discrete applications on the same hardware.
  • Containers can be shared between the applications
  • Simple to deploy and easy to maintain

Check difference between Docker and Kubernetes 

3. What is a Docker HUB?

Docker containers are made from the instance of the Docker images. The Docker containers are stored on the kernel of the given operating system. We need to store the images also, and the registry or collection of the Docker images is called the Docker hub.

4. How does Docker help in building environment-agnostic systems?

It is the unique selling point of the Docker that it can run on any environment, irrespective of the systems. The three main attributes that make the Docker the environment-agnostic systems are Volume, environment variable injection, and read-only file systems.

5. What does a Docker container comprise of?

A Docker container is typically an instance of a Docker image and is the execution state of the image. It consists of complete application packages such as libraries, executables, and other dependencies. A Docker container shares the kernel space with several other containers on the same host operating systems. Docker container is used to package and ship the applications and the container can run anywhere, irrespective of the environment.

Are you ready for the interview?

As you have seen the Docker is used for many web applications and other applications and has a lot of benefits, you must know more Docker interview questions for experienced to get the right job with market pay. 

Docker is one of the containerization technology used extensively in DevOps. We have seen some questions and answers that can be asked in the interview and thus can be important for you in getting a break in an organization in DevOps roles. To learn more we recommend you take the DevOps online course with StarAgile that provides complete details about DevOps framework and its tools.