Top Docker Interview Questions and Answers for 2023

Docker is an open-source containerization platform. It is used for creating, deploying, and running applications. Docker helps organizations streamline their diverse applications and improve business agility. As more and more organizations continue to use multi-cloud applications on a wide scale, employers are looking for IT professionals with Docker skills who can assist in migrating, deploying, and managing containers.

The demand for IT professionals with Docker experience is growing fast. In this blog, we have listed the frequently asked Docker interview questions. This list of interview questions on Docker for freshers and experienced candidates will prepare you to answer different questions that may be asked in your next interview.

Check out the best Docker Courses Online

Top Docker Interview Questions and Answers

Here is the list of the most important Docker interview questions and answers

Q1. What is Docker? What are its features?

Ans. Docker is a powerful open-source software that runs on Linux and Windows. It is used to automate the creation and deployment of applications in containers. We can say that it is a lightweight form of virtualization.

Docker enables users to package their applications and its dependencies together into containers. It enables users to separate their applications from their infrastructure.

Features of Docker

• Easy Configuration
• Improved Software Delivery
• Application Isolation
• Quick scaling of Systems
• Security Management
• Version control
• Software-defined Networking
• Improved Developer Productivity
• Operational Efficiencies

To learn more about Docker, read our post – What is Docker?

Also read: Different Types of Docker Containers

Read: Container vs Virtual Machine

Q2. Explain the main components of Docker.

Ans. Docker has three main components:

Docker Client: It helps users to interact with Docker. The client offers a command-line interface (CLI), allowing users to create, run, and stop application commands to a Docker daemon. The client can be on the same host as the daemon. It can also connect to a daemon on a remote host. A client can interact with more than one daemon.

Docker Host: It provides a complete environment to run applications. It comprises Docker daemon, containers, networks, storage, and images. Docker Registry:

This is the location where you can store and download Docker images. There are two types of registries, a public registry and a private registry. Docker Hub is the default location of docker images.

When executing the docker push command, the image is stored on the configured registry. When we execute the docker pull or run commands, the image is pulled from the configured registry.

Must Read: Top Kubernetes Interview Questions and Answers

Q3. What is a container?

Ans. A container is a standard software unit bundled with dependencies to expedite the application deployment process in a reliable manner between different computing platforms. A docker can be visualized as a big ship, i.e., carrying huge boxes of products, i.e., containers. These containers do not require the installation of a separate operating system. Docker uses the kernel’s resources and functionality to allocate them for CPU and memory and separate namespaces for isolating the application’s view of the operating system.

Q4. What are the differences between virtualization and containerization?

Ans. Virtualization and containerization are the commonly used mechanisms to host applications in a computer system. The differences between virtualization and containerization are:

Virtualization	Containerization
This technology enables users to run multiple operating systems on the hardware of a single physical server.	It allows users to deploy multiple applications using the same operating system on a single VM.
Heavyweight.	Lightweight.
Not portable.	Portable.
Hardware-level isolation	Process-level isolation.
More secure.	Less secure.
Slow provisioning.	Fast provisioning.

For more information read: A Comprehensive Comparison of Containerization and Virtualization

Q5. What is a docker image?

Ans. A Docker image is a read-only template with instructions for creating containers that can run on Docker. It is an executable package (a collection of files or layers) that bundles all the necessities, such as application code, dependencies, software packages, and more, required to set up a completely functional container environment. There are two methods to create a Docker image:

• Interactive
• Dockerfile

Q6. What is a DockerFile?

Ans. A DockerFile is a text document with all commands that must be run to build an image. In simpler terms, a Dockerfile refers to the build instructions to build the image. The instructions will execute in the order in which they are written.

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Q7. Which command is used to export a docker image as an archive?

Ans. We can export a docker image as an archive using the docker save command.

Syntax

docker save -o <exported_name>.tar <container-name>

Q8. Which command imports a pre-exported Docker image into another Docker host?

Ans. Using the docker load command, we can import a pre-exported Docker image into another Docker host.

Syntax

Q9. How to delete a container?

Ans. We can follow the below steps for deleting a container:

– docker stop <container_id>

– docker rm <container_id>

Q10. What is the command to see all running containers?

Ans. To see all the running containers, we use the below command :

Q11. Which command is used to stop the docker container?

Ans. The below command stops the docker container:

Also Read: Top 8 Highest Paying IT Certifications

Q12. Write the command to run the image as a container.

Ans. To run the image as a container, we use the below command:

Q13. How to build a Dockerfile?

Ans. we use the docker build command to build a Dockerfile

Syntax

Q14. What is Hypervisor?

Ans. A hypervisor is also known as a virtual machine monitor or VMM. The software enables users to create a virtual environment where the guest virtual machines (VMs) operate by virtually sharing their resources.

A hypervisor controls the guest systems and ensures that necessary resources are allocated to the guests. There are two types of hypervisors:

• Native: They run directly on the underlying host system. It provides direct access to the host system’s hardware and does not need a base server operating system.
• Hosted: They use the underlying host operating system.

Also Read: Most In Demand Tech Skills to Master

Q15. What are the steps in the lifecycle of a Docker container?

Ans. The lifecycle of a Docker container consists of the following stages:

1. Create a container: A container can be run later with the required image.

2. Run the container: Run the Docker container with the required image and specified command or process. We use the ‘-d’ flag to run the container in the background.

3. Pause the container: It pauses the processes inside the container.

4. Unpause the container: It unpauses the processes running inside it.

5. Start the container: It starts those containers in the stop state.

6. Stop the container: Stops and processes running inside the container.

7. Restart the container: To restart the container and the processes running inside the container.

8. Kill the container: To kill the running container

9. Destroy the container: It should be done when the container stops.

docker rm <container-id/name>

Q16. Explain some advanced Docker commands.

Ans. Some of the advanced Docker commands are:

Command	Description
docker checkpoint	manages checkpoints
docker pull <image>	pulls docker repository images
docker stats [OPTIONS] [CONTAINER…]	shows resource usage statistics
docker info [OPTIONS]	shows system-wide information
docker-machine upgrade default	upgrade the docker to the latest version

Q17. What is Docker Machine?

Ans. A tool that allows you to install docker engine on virtual hosts and these hosts can be managed by docker-machine commands.

Q18. Is it possible to remove a paused container from the docker?

Ans. NO, you can’t remove a paused container from the docker. The container must have to be in a stop state before it can be removed.

Q19. What is the maximum number of containers that can run per host?

Ans. It can be as many as you want. There is no restriction on the number of containers, but as every container needs storage spaces, CPU, and memory that hardware supports. Containers are lightweight, but it depends on the host OS.

Conclusion

Docker is a popular tool that enables users to create, deploy, and run their applications seamlessly. It is widely used by many developers and organizations today. Docker skills are one of the most in-demand skills in the job market. We hope this Docker interview questions blog will help you prepare well for your upcoming interview and land a sought-after role in this field.