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30+ Docker interview questions and answers

Shailendra Chauhan  Print   8 min read  
31 Jul 2021
 
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 Docker got released in 2013 and by now it has become one of the prominent container platforms. The rising demand for Docker depicts a significant raise in the corresponding job openings. To secure a job in the name, an individual needs to be prepared for the Docker Interview questions and answers. They are discussed below:

Docker interview questions and answers

1. What is Docker?

A: Docker is a well-known containerization platform that packs your application as well as all its dependencies collectively in the structure of containers. As a result, it is guaranteed that your application works flawlessly whether the environment is test or development, or production. The Docker container contains a piece of software in a whole file system. This system comprises all components essential for operation.

2. Why is DevOps inevitable?

A: In recent times, instead of launching a huge assortment of features, companies are attempting to check whether tiny features can be conveyed to their customers via a sequence of release trains. The same offers plenty of benefits like instant feedback from customers, enhanced quality of the software, and many more. Consequently, it provides contentment to customers. DevOps fulfills requirements like reduction in failure rate of new launches, boost in deployment frequency, reduction in lead time amongst fixes, and more. So, the software delivery is seamless.

3. What are the key features of Docker?

A: Its key features include flawless modeling, version control, application agility, placement, developer productivity, and operational efficiencies.s

4. What it means by Docker Container?

A: A container is the fundamental software unit that stores the code as well as all of its dependencies. It assists to let the application operate reliably, flawlessly, and speedily amongst the computing ecosystems. A Docker container is known as an executable package of the software which contains all components essential to execute an application. It contains libraries, system tools, runtime, code, and settings.

5. How to create a Docker container?

A: Use the below command and a Docker image to create a Docker container. docker run -t -i command name The aforementioned command creates the container as well as starts it.

6. How Docker is unique from other container technologies?

A: Docker is prevalent as one of the most recent container technologies and gained immense popularity. It is built in the cloud era and encompasses a myriad of novel features that were lacking in old container technologies. Out of its various features, one of the greatest ones is that it can operate on any infrastructure –Cloud or the home machine.

7. What is Docker Hub?

A: The Docker containers are created using Docker images. A registry is vital to have so that the Docker images become live and this registry is the Docker Hub. Docker Hub lets users choose images. It is also beneficial to make tailored images and containers.

8. What is Docker image?

A: Docker image is nothing but the source of Docker container. The Docker images are primarily useful to create containers. With the build command, the images are created and they will generate a container when launched with run. It is observed that the Docker images are saved inside a Docker registry. The corresponding images are made up of layers of other images. So, the data loss is minimal during the transfer of images across the network.

9. Describe the components of Docker Architecture:

A: The 3 key components in Docker architecture are host, client, and registry. They are explained below: Host- It stores the Docker Daemon, Containers, and Images. The Docker Daemon sets up a link with the Registry whereas the Docker Images works as metadata for the applications that are stored in the Docker Containers. Client- This component executes operations to establish communication with the Docker Host. Registry- It is useful to hold the Docker Images. Docker Cloud and Docker Hub are public registries that can be used by anybody.

10. What is the Docker Registry?

A: Docker Registry is the place where all Docker Images are saved. The Docker Hub is known as a public registry that works as the default storage for such images. The Docker Hub is the most considerable public registry of the image containers. It is constantly maintained by a huge number of developers and several individual contributors.

11. What is Docker Swarm?

A: It is native clustering for Docker that transforms a group of Docker hosts into a single, practical Docker host. Those tools that already communes with a Docker daemon can use Docker Swarm to level up to multiple hosts.

12. What is Docker Engine?

A: Docker engine (also known as Docker daemon) represents the server. The Docker engine and the clients must be operated on the identical or remote host, that can communicate via command-line client binary as well as full RESTful API.

13. What is a Docker Namespace?

A: Namespace includes a layer of isolation in Docker containers. To ensure portability, Docker provides diverse namespaces. It makes sure there is no adverse effect to the basic host system. Names of some of the namespace types which Docker supports are PID, IPC, Mount, User, and Network

14. What is Docker Compose?

It is a YAML file that stores details about the networks, services, and volumes for the creation of the Docker application.

15. For Docker Container, what type of applications is more suitable - Stateless or Stateful?

A: Stateless applications are better than Stateful applications for Docker Container. Stateless applications allow the creation of one container from the application you are using and extract the configurable state parameters of the app. After this is done, it is possible to execute the same container with various other production parameters and different environments.

16. Which networks are available as default in Docker?

A: The default networks available in Docker are bridge, none, and host. The ‘bridge’ is the default network that connects the containers if the network is not specified. The ‘none’ network connects to a container-specific network stack which lacks a network interface. The ‘host’ network connects to the network stack of the host.

17. Which command should be used to check all running containers in Docker?

A: $ docker ps

18. Name the command to stop the docker container:

A: $ sudo docker stop container name

19. Name the command to run the image as a container:

A: $ sudo docker run -i -t alpine /bin/bash

20. Which are the common instructions in Dockerfile?

A: The common instructions present in Dockerfile are: FROM, RUN, LABEL, and CMD.

21. What it means by Docker object labels?

A: The Docker object labels are the mechanism for adding metadata to docker objects like containers, images, volumes, Local daemons, network, swarm services, and swam nodes.

22. What is Hypervisor?

A: The hypervisor manages the creation of the virtual environment on which the guest virtual machines run. Moreover, it monitors the guest systems and ascertains that the required number of resources is allocated to the guests.

23. What is the difference between Docker Layer and Image?

A: A Docker image is created from a sequence of read-only layers. A Docker layer shows an instruction in the Dockerfile of the image.

24. How to supervise Docker in production?

A: To monitor Docker in production, it comes with tools like docker events and docker stats. These commands are useful to obtain reports on significant statistics.

25. What is Virtualization?

A: Virtualization is a system of logically segmenting mainframes for allowing multiple applications to execute at once. With virtualization, it is possible to execute two different operating systems on the same hardware.

26. What is CNM?

A: CNM is the abbreviation of Container Networking Model. Basically, it is a standard from Docker, Inc. that creates the foundation of container networking within a Docker environment.

27. How to establish communication happen between Docker Daemon and Docker client?

A: The communication between Docker Daemon and Docker client can be established with the combination of socket.IO, Rest API, and TCP.

28. How to scale Docker containers?

A: It is allowed to scale your Docker containers to any specific level, reaching up to millions of containers. The necessary condition is that the containers require the OS and the memory throughout the operation. So, there must be no compromise in these requirements.

29. What are the various volume mount types accessible in Docker?

A: Bind mounts are available and they can be saved anywhere on the host system

30. Is there any limit on the number of containers running per host?

A: No, there can be any number of containers running per host, as you wish. Docker does not employ any limit but keeps in mind that every container demands memory, storage space, and CPU. Also, the application size needs to be considered.

31. What are the Docker alternatives?

A: Some of the alternatives to Docker are Kubernetes, Virtual Box, Open Container Initiative (OCI), Rancher, Vagrant, Apache Mesos, etc.

| Kubernetes vs Docker: Analyzing The Differences

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