10 must know Docker interview questions and answers

Are you a proficient Docker developer who wants to work in a top Silicon Valley company, or are you looking for brilliant Docker developers to assemble your dream team? Look no further. These are the 10 must-know Docker interview questions prepared for you to ace your Docker interview.

Last updated on Mar 22, 2023

Docker's popularity has skyrocketed during the last several years. What is the explanation behind this? It has altered the way software is developed. Docker's containers help achieve massive economies of scale, making programming scalable while maintaining a user-friendly experience. This is why you would need to brush up on your Docker knowledge to ace your Docker interview. As a recruiter, the rise of popularity of Docker demands more proficient Docker developers. Therefore, the given Docker interview questions and answers perfectly encompass the needs of both the candidate and the recruiter.

Docker developer interview questions and answers


Explain Docker namespace.

A namespace is a Linux kernel feature that guarantees the partitioning of kernel resources is mutually exclusive. Namespaces provide a layer of separation between containers, which is the primary principle of containerization. The namespaces in Docker ensure the portability of containers and that the containers do not affect the underlying host. PID, Mount, User, Network, and IPC are examples of namespace types that Docker presently supports.


Talk about hypervisors and their functions.

A hypervisor, also known as the Virtual Machine Monitor, is a piece of software that allows virtualization to take place. This splits the host system's resources and distributes them to each deployed guest environment.

This implies that on a single host system, different operating systems may be installed. There are two types of hypervisors:

  • Native Hypervisor: Also known as a Bare-metal Hypervisor, this form of hypervisor operates directly on the underlying host system, allowing direct access to the host hardware and eliminating the need for a base OS.
  • Hosted Hypervisor: This form uses the underlying host operating system, which already has an operating system installed.


List down the components of Docker.

The following are the three primary Docker components:

  • Docker Client: Performs To communicate with the Docker Host, use the Docker build and run procedures. The Docker command then uses the Docker API to conduct any queries that need to be run.

  • Docker Host: It is a service that allows you to host Docker containers. The Docker daemon, containers, and accompanying images are all included in this package. A connection is established between the Docker daemon and the Registry. The type of metadata related to containerized apps is saved pictures.

  • Registry: Docker images are kept in this folder. A public register and a private registry are also available. Docker Hub and Docker Cloud are two open registries that anybody can utilize.


How can you remove all stopped containers and unused networks in Docker?

Prune is a command that gets rid of all of your stopped containers, unused networks, caches, and hanging images. Prune is one of Docker's most helpful commands. The syntax is, prune docker system $.


When a container exists, is it possible for you to lose data?

No, it is impossible to lose any data as long as a container exists. Until the said container is deleted by you, you will not lose any data stored in that container.


Does Docker provide support for IPV6?

Docker does, in fact, support IPv6. Only Docker daemons running on Linux servers support IPv6 networking. However, if you want the Docker daemon to support IPv6, you must edit /etc/docker/daemon.json and change the ipv6 key to true.


Is it possible for a container to restart by itself?

Yes, but only when specific docker-defined rules are used in conjunction with the docker run command. The policies that are accessible are as follows:

  • Off: If the container is stopped or fails, it will not be resumed.
  • On-failure: In this case, the container restarts itself only if it encounters failures unrelated to the user.
  • Unless-stopped: This policy assures that a container may only resume when the user issues a command to stop it.
  • Always: In this form of policy, regardless of failure or stoppage, the container is always resumed.

This is how you use these policies:

docker run -dit — restart [restart-policy-value] [container_name]


Differentiate between Container Logging and Daemon Logging.

Logging is supported at two levels in Docker: at the Daemon level and the Container level.

  • Daemon Logging

Debug, Info, Error, and Fatal are the four levels of logging used by daemons. Debug keeps track of everything that happened throughout the daemon's operation. During the execution of the daemon process, info carries all of the information as well as error information. Errors refer to errors that happened during the daemon process' execution. Fatal refers to execution faults that resulted in death.

  • Container Level Logging

You can perform container level logging by executing this command: sudo docker run –it <container_name> /bin/bash To check for container-level logs, enter: sudo docker logs <container_id>.


How will you use Docker for multiple application environments?

Docker's compose capability will come in handy here. You should describe various services, networks, and containers, as well as volume mapping, in a tidy manner in the docker-compose file, and then just run the command "docker-compose up." You need to describe the requirements and processes which are server-specific to execute the application, especially when there are so many environments involved. It may be dev, staging, uat, or production servers. For example, you should create environment-specific docker-compose files with the name "docker-compose.environment.yml" and then based on the environment, set it up and execute the application.


Is there a limit on how many containers you can run in Docker?

The amount of containers that may be run under Docker has no explicitly specified limit. But it all relies on the constraints, particularly the hardware constraints. The size of the program and the number of CPU resources available are two major determinants of this restriction. If your program isn't too large and you have plenty of CPU resources, we can run a lot of containers.

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Wrapping up

Following these Docker interview questions, you are now ready for your Docker interview from a technical standpoint. However, in order to ace your Docker interview, this is not enough. As a recruiter, who is looking for excellent docker developers that would fit perfectly in the company, you need to make sure they have really good soft skills. Therefore, it is important that apart from preparing docker interview questions, you would also need to craft some questions that would gauge a candidate’s soft skills, in how well they would fit in the present work environment, and how well they would work in a team. As a Docker developer, it is crucial that apart from practicing the above Docker interview questions, you would also need to brush up on your soft skills. You need to be technically prepared and also have great soft skills in order to nail your Docker interview.

If you are ready to give your Docker interview and want to place a job at a top Silicon Valley company, head over to Turing and apply as a developer! Turing.com provides the top 1% of developers from around the world, so if you want to hire the best of the best, join hands with Turing.

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