Docker Interview Questions: What You Need to Know

Docker is a powerful and popular technology that makes it easier to develop, deploy and manage applications. It has been around for about few years now, so you can be sure there are plenty of interview questions out there! This article will provide some of the most common Docker interview questions with their answers.

1. What is docker?

Ans. Docker is an open-source engine that automates the deployment of applications inside software containers. These containers can then run on any machine, regardless of its underlying operating system or architecture. Docker was originally developed in 2013 by a team at Switzerland’s dotCloud but quickly grew to be one of the most popular tools for deploying web apps and cloud services (IDC survey).

2. How can I get started with docker?

Ans. You will need to install Docker on your machine and then either pull an image from a registry or create one by using the command-line tool, called “Dockerfile” which is included in every installation of Docker).

3. What is a docker registry?

Ans. Docker registries are public or private image repositories that store Docker images for reuse (e.g., to deploy applications). These can be managed by third parties and accessed over the internet as well as through an organization’s own infrastructure.

4. What are the advantages of docker?

Ans. Docker’s main advantage is its speed, simplicity, and efficiency. In a nutshell: it makes your life easier by automating everything from development to deployment so you can stay focused on building an awesome app rather than fighting with configuration issues or wasting time spinning up virtual machines for testing purposes. And it’s not just the time it saves you – using Docker also enables teams of developers to work on a single application without any conflicts and with up-to-date versions.

5. How can I port my app?

Ans. The best way is to use docker container virtualization, which creates an isolated environment for your apps that are identical no matter where they’re deployed.

6. What is a dockerfile entry?

Ans. A Dockerfile typically starts with an instruction that identifies which base image to use. You may then add one or more commands, for instance: installing packages, defining environment variables, and copying files.

7. What is a docker container?

Ans. A Docker container starts with an image and then adds layers on top of that, each containing software to be deployed. It also specifies how much memory the processes inside it can use, where data should go when it needs more hard drive space etc.

8. What is Containerization?

Ans. The whole and soul of Docker is the container mechanism, which means you can expect this question in your interview. To answer this question, you can simply go ahead with a crisp, clear, and precise answer:

Containerization is a lightweight alternative to full machine virtualization. It involves the encapsulation of an application in a container with its own operating environment. One of the many benefits of loading an application onto a virtual machine is that it can be run on any suitable physical machine without worrying about any kind of dependencies.

9. What is Virtualization?

Ans. The method of strategically dividing mini-frames is known as virtualization. Virtualization allows you to run multiple applications simultaneously, without any glitches. A software called Hypervisor facilitates this splitting, and the virtual environment created by the Hypervisor is called the Virtual Machine.

10. State the difference between Containerization and Virtualization.

Ans. Once you have defined Containerization and Virtualization, stating the difference between both concepts should not be difficult. However, to put it forth briefly, you can choose to say:

The container offers you an isolated environment required to run the application. In containerization, the entire user space is wholly dedicated to the application itself. On the other hand, in virtualization, the Hypervisors provide access to an entire virtual machine to the guest.

11. What are docker images?

Ans. An image is a read-only template used as the starting point from which you build your final container application package. The idea behind it is that each time you need to deploy something – all you have to do is create another instance based on this image rather than having to copy files over again every time. This way changes occur only in the final container application package, not on any of its intermediate copies.

12. What is a Dockerfile?

Ans. A Dockerfile is a text document that contains all the commands needed to create a new container application package from an image. You may not need to create one yourself if you’re using an official base image instead – but it’s still useful for learning purposes.

13. What is a Docker Engine?

Ans. Docker Engine, also known as the Docker Daemon represents the server. It supports the tasks and workflow involved to build, ship, and run container-based applications. The engine provides a CLI (Client Line Interface), enabling users to interact with the daemon through the Docker Engine API.

14. What is a Docker Swarm?

Ans. Native clustering for Docker is termed as Docker Swarm. This swarm turns a pool of Docker hosts into a single, virtual Docker host. Any tool that already communicates with the Docker daemon can leverage the Docker Swarm to instantly and transparently scale multiple hosts.

15. Describe Docker Compose

Ans. A YAML file, Docker Compose contains details about services, networks, and volumes for setting up the Docker application. Using the Docker Compose, you can create separate containers and host them. Not only this, but Docker Compose also doubles up as the link of communication between them.

16. What is Docker Hub?

Ans. Docker hub is a cloud-based registry. Docker hub helps you to link to the code repositories, allowing you to build, test, and store your image on the Docker Cloud. It also helps you deploy the image to your host, facilitating a seamless transfer.

17. How is Docker different from other methods of containerization?

Ans. In Docker, the containers can be easily deployed in any cloud platform. As compared to other containerization technologies, Docker allows you to seamlessly run multiple applications on the same hardware simultaneously. Developer-friendly, Docker can quickly create ready-to-run containerized applications, making the whole process of managing and deploying applications a lot easier.

18. How many containers can run per host?

Ans. There is no limitation on the number of containers per host. Docker gives you the flexibility of as many containers on a given host. Containers are extremely lightweight, but you cannot deny the fact that they are heavily dependent on the host OS. This means we need to consider different aspects such as memory, CPU, and memory, as the number of hosting capability is completely dependent on it.

19. What platforms does Docker run on?

Ans. Docker runs on various Linux administrations, such as Gentoo and Archlinux among others. It is also compatible with Cloud platforms such as Google Compute Engine and Rackspace.

20. Will Docker replace Cloud technology?

Ans. Docker and Cloud have different strengths of their own. Even though the popularity of Docker is increasing, Cloud too, has amped up the game with its range of new features. Despite all this, Docker will never be replaced by the Cloud. In fact, organizations should be in a position to leverage the best of both Docker and Cloud for their benefit.


To sum up, you can now be confident when interviewing for a job. You know what questions to expect and how best to answer them! So get out there and put your Docker skills on display for the world to see!

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