Posted on : 17 May, 2021, 03:44:29 PM

Top 50 Docker Interview Questions And Answers

Top 50 Docker Interview Questions And Answers

Docker is setting off a clear path on core development capabilities, establishing a conversation between containers and cross-service management, which is also known as libcontainer, libchan, and libswarm. Meanwhile, industries are already showing a willingness for their own ecosystem to consume with the Orchard Labs acquisition. 

Docker was released in 2013 and is known as a helpful tool for application packaging, shipping, and running in containers. Many big companies such as IBM, Google, VMware, Amazon, and Red Hat, etc., have looked towards Docker as the go-to technology for containers that clears that it is high time to learn and make a career out of it. So go ahead and take advantage of all the latest job openings for docker professionals with this blog that Wissenhive designed with the industry expert includes the top 50 frequently asked Docker interview questions.


1. Explain Docker?

Docker refers to a lightweight open-source technology used for containerization. It has gained widespread popularity in the application packing world and cloud computing services. Docker allows an individual to automate the application deployment in portable and lightweight containers.



2. What are some of the important features of Docker?

There are six different features included in Docker.

  • Placement/Affinity
  • Application Agility
  • Version control
  • Developer Productivity
  • Easy Modeling
  • Operational Efficiencies


3. What are the key drawbacks of Docker?

There are few drawbacks of Docker, which includes 

  • Docker does not provide any storage option.
  • No automatic rescheduling feature available for inactive Nodes
  • Offer a poor monitoring option
  • Complicated horizontal automatic scaling set up


4. What do you understand about Docker containers?

A Docker container refers to a standard unit of the software that holds, operates, and packages up code with its dependencies to make the application run quickly, smoothly, and reliably from one computing ecosystem to another. An image contained in a docker container is an executable, standalone, and lightweight software package that combines everything needed to run an application, such as system tools, System setting, system libraries, runtime, and code.


5. What are the uses of the Docker container?

There are mainly four uses of Docker container, and those are

  • It allows an easy and efficient initial setup.
  • Offers individual to describe the lifecycle of an application in detail
  • Documentation presents each bit of information and data.
  • Easy interaction and configuration with Docker Compose


6. What are the four states in a Docker Container?

  • Running
  • Restarting
  • Paused
  • Exited


7. Explain the lifecycle of a Docker Container?

  • Building a container
  • Operating the container
  • Pausing the container (optional)
  • Un-pausing the container (optional)
  • Starting the container
  • Stopping the container
  • Restarting the container
  • Removing the container
  • Destroying the container

Lifecycle of a Docker Container

8. What are container orchestration and its uses?

Container orchestration helps in maintaining and managing the containers running in a large and dynamic environment. It can automate and control the tasks such as

  • Load balancing
  • Scaling of containers
  • Monitoring the health of hosts and containers
  • Switching containers from one host to another when the host lacks resources or unavailable.
  • Allocation of resources between containers
  • Provisioning and deployment of containers


9. What are Docker images?

The Docker images help in building docker containers, and individuals can create the Docker images with the build command. Due to this procedure, it creates a container that starts when it begins to run. Docker registry helps in storing all the built images in Docker.


10. What is the Docker registry in detail?

All the Docker images are stored in Docker Registry. The Docker Hub refers to a public registry that is the default storage for docker images. Docker Cloud is another public registry, and the docker hub is one of the most significant public storehouses for image containers, which is maintained and managed by a large number of developers consistently along with individual contributors.


11. What are Linux administration platforms where docker runs?

  • RHEL 6.5+
  • CentOS 6+
  • openSUSE 12.3+
  • CRUX 3.0+
  • Ubuntu 12.04, 13.04 et al
  • Fedora 19/20+
  • Gentoo
  • ArchLinux


12. What is Hypervisor?

Hypervisor refers to software that helps in presenting thoughts through visualization, which is also known as Virtual Machine Monitor. It divides the host system into several systems and allocates the resources to every distributed virtual environment. An individual can have the various OS on a particular separate host system through this.


13. What is Virtualization?

Virtualization is the process used to build a software-based practical version of something such as servers, compute storage, application, etc. These environments or virtual versions are designed from a particular physical hardware device or system. Virtualization allows users to split one system into various sections representing distinct, separate individual systems. A software named Hypervisor performs this sort of splitting. The virtual environment produced by the Hypervisor is termed a Virtual Machine.


14. What are the different types of Virtualization?

There are mainly three different types of Virtualization.

  • Paravirtualization
  • Emulation
  • Container-based virtualization


15. What is Docker Hub?

Docker images work on generating docker containers. There must be a registry where docker images remain live on the device. This registry is known as Docker Hub. An individual can choose any Docker Hub images and utilize them to perform customized containers and images. Currently, the Docker Hub is one of the world’s largest public repositories of image containers

Docker Hub

16. What is Docker Architecture?

Docker Architecture is made up of or consists of a Docker Engine that refers to a client-server application with some major components:

  • Daemon process
  • Command-line interface

Docker Architecture

17. What are the main components included in Docker architecture?

The three main components of Docker architecture are 

  • Host
  • Client
  • Registry


18. What is Dockerfile?

A Dockerfile is a text report or document which holds all the commands, and an operator could name or call to assemble an image on the command line. Users can design an automatic build that performs numerous command-line instructions in succession by using Docker build.


19. What are the common instructions used for Dockerfile?

The common instructions used in Dockerfile are

  • FROM
  • RUN
  • CMD


20. What is Docker Compose?

Docker Compose is a YAML file containing details about the networks, services, and volumes for setting and fixing up the Docker application. Users can use Docker Compose to build particular containers separately, hosting them and preparing them to interact with each other. Each and every container will present a port for interacting and communicating with other containers.


21. What is Docker Swarm?

Docker Swarm refers to a native clustering for Docker, which helps in turning a pool of docker hosts into a virtual, single Docker host. It serves the standard Docker API, and any tools that are already interacting and communicating with Daemon of Docker can use Docker Swarm to scale to multiple hosts transparently.


22. What is a Docker Namespace?

A Namespace is a feature of Linux and plays an important role in containers. It helps in adding the isolation layer in containers. Docker gives multiple namespaces in order to stay portable, manageable,  and not harm the underlying host of the system. Some types of Namespace supported by Docker include Mount, User, PID, IPC, and Network.


23. What is Docker Machine?

Docker machine is a mechanism that allows users on virtual hosts to install Docker Engine. These virtual hosts can now be managed using the commands of docker-machine. Docker machines also give individuals provision Clusters of Docker Swarm.


24. What do you mean by the memory-swap flag?

Memory-swap refers to a modified flag process that only has worth if the memory is also set. Swap provides the container to communicate and express memory specification and requirements to disk when the container has consumed all the RAM that is available to it.


25. What is the Docker system prune?

This command is “$ docker system prune” used for removing all the paused or stopped containers, each and every network that is not in use, all build caches and all dangling images. It is known as one of the most useful commands in docker.


26. What are some of the important Docker commands?

There are five different types of Docker commands, and those are

  • Build: for creating an image file for Docker
  • Create: for the creation of a new container
  • Commit: used for creating a new image from the container changes
  • Kill: used for killing a container
  • Dockerd: for launching Docker daemon


27. Why is Docker Monitoring important?

  • Docker monitoring assists in identifying problems proactively that would help in avoiding system outages.
  • The monitoring time-series data present insights to the fine-tune applications for better robustness and performance.
  • The container-based environment changes are essential, and the impact of that too gets monitored and controlled indirectly.
  • With the complete monitoring in place, modifications could be safely rolled out as problems will be detected early on and be resolved immediately before that converts into the root cause in an outage.


28. What do you mean by Docker Swarm?

Docker swarm is a native tool that is used for scheduling and clustering Docker containers. IT supervisors, developers, use docker swarm to build, manage and maintain a set of nodes in the solitary virtual system or Docker.


29. What do you mean by Docker Objects?

Docker objects include three different terms, and those are Docker images, docker services, and Docker containers.

  • Images are a read-only template with specific instructions for building a Docker container.
  • Services help enable the containers to scale across various Docker Daemons that all work together as a swarm.
  • Containers manage a runnable instance of an image.


30. What are the networks available in Docker by default?

There are three different types of the default network in Docker, and those are

  • Bridge: Default network that the containers connect to if the network is not specified
  • Host: Connects to the network stack of the host
  • None: helps in connecting with the container-specific network that stacks lacking an interface of the network.


31. What are Docker object labels?

Docker object labels is a process that helps in applying metadata to docker objects including,

  • Images
  • Containers
  • Local daemons
  • Volumes
  • Networks
  • Swarm nodes
  • Swarm services


32. How does communication establish between Docker Daemon and Docker clients?

The communication happens between Docker Daemon and Docker Client with the combination of 

  • TCP
  • Rest API
  • socket.IO


33. What are the steps included in a deployment process for Dockerized Apps stored in a Git Repo?

When there are changes in the deployment process within a production environment, then the basic deployment process is followed.

  • Develop an application by Docker Build, which is located in the code directory
  • Pushes the all-new images to registry docker
  • Perform the image testing
  • Notify the application server that is remote to take image hold from the registry and run it
  • Stopping the older container
  • Swapping Port in HTTP proxy


34. What are the similarities between Docker and Virtual Machine?

Scope Docker Virtual Machine
Process One container can’t see processes in another container. Process in on Virtual Machine can’t see processes in another VM.
Root File Every container has its own root file system Every Virtual Machine has its own root filesystem.
Virtual Network Adapter Can get a virtual network adapter with the separate ports and IP Can get its own virtual network adapter
Running Instances Docker containers are running instances of Docker Image A virtual machine is a running instance of physical files (.VMDK and . VMS)
Host OS It can be different from Container OS Can be the difference from guest OS


35. Differentiate between Docker and Virtual Machine

Scope Docker Virtual Machine
Operating System All containers share the same host kernel Every Virtual Machine runs its own OS
Boot up timing In seconds In seconds
Snapshots Images are incrementally built on top of another layer with lots of snapshots/images. Virtual machines use snapshots or images sparingly.
Version Controlled Images can be different and version-controlled Docker Hub such as GITHUB. Neither effective differences nor version controlled.
Running in Laptop Able to run many Docker containers on a laptop Not able to run more than a couple of Virtual machines on a laptop.


36. What are the different ways used for configuring Docker Daemon?

There are mainly two different ways to configure the Docker Daemon, and those are by using a 

  • JSON configuration file
  • Using flags when dockerd start


37. What is the importance of using container networking?

  • Containers need to communicate to the external world. 
  • Reach Containers to use the service that Containers provide from the external world.
  • Inter-container connectivity across hosts and in the same host 
  • Provides containers to talk with the host machine. 
  • Identify services automatically provided by containers. 
  • Helps in providing secure multi-tenant services
  • Loading balance traffic between several containers through services


38. What is the main goal of Docker_Host?

IT contains Docker images, containers, and daemons, which offers a complete environment for executing and running the applications.


39. What do you understand about CNM?

The full form of CNM is Container Networking Model, which is the specification and standard from Docker, Inc. that forms a container networking basis in the Docker environment. It is one of the approaches of Docker to provide networking to the container with support from various network drivers.


40. What are the major components of the Container Networking Model?

  • Network
  • Sandbox 
  • Endpoint


41. How is the Bridge network different from the Overlay network?

Bridge networks help in connecting two different networks while building a particular aggregate network from various network segments or communication networks.

Bridge Network

Overlay networks are used for building a virtual network between two separate hosts. Virtual since networks are created over an existing network.

Overlay Networks

Bridge networks can provide or work with a single host, while overlay networks are designed for multiple hosts.


42. Differentiate between Hyper-V container and Windows server container

Scope Hyper-V Container Windows Server Container
Basic Image Can be different from the host Same as host
Kernel Independent kernel Shared with host
Admin within Container Yes No
Resource Management New services started inside Same sharing with the host
IP New IP address per instance New IP address per instance or shared host's
Domain join support Yes No
Machine Identify Different Same as host
Support for Block Storage No Yes


43. What are ENTRYPOINT and CMD in a Dockerfile? 

In a Dockerfile, both ENTRYPOINT and CMD instructions define that command will be administered while running containers. There are some rules for their cooperation, such as

  • The Dockerfile should specify and define at least one command from ENTRYPOINT or CMD.
  • When running the alternative argument with the container, CMD will be overridden.
  • While working with the container as an executable, ENTRYPOINT needs to be adequately defined.


44. How to monitor Docker in production?

Docker implements functionalities such as docker events and docker stats for monitoring Docker in production. Docker stats include memory and CPU usage of the container. Docker events work on providing detailed information about the activities that are taking place in the docker daemon.


45. Describe the process for running an application inside the container of Linux

  • Install and run Docker
  • Linux based OS (Fetch Fedora 21) base image from the hub of Docker 
  • Checking containers in the system
  • Go inside a Docker container
  • Starting or stopping Docker container
  • Loading application in the image of Docker base
  • Run container in interactive mode using your new image 
  • Removing image or container


46. Explain the different types of basic docker commands

  • Docker start: starts one or more containers
  • Docker stop: stops running containers
  • Docker push: pushes repository or image to a registry
  • Docker run: runs a command in a new container
  • Docker search: searches for an image in a docker hub
  • Docker commit: commits new image
  • Docker pull: pulls repository or image from a registry.


47. What are the different types of mount kinds available in Docker?

There are three different types of mounts available in docker.

  • Bind mounts
  • tmpfs mount
  • Volume mount


48. What modifications are expected in your docker-compose file while transferring it to the production?

  • Removing volume bindings, so that code cannot be changed and stays inside the container.
  • Specifying the restart policy
  • Binding to various ports on the host
  • Adding extra services like log aggregator


49. Can docker be used in production with cloud platforms?

  • Google Compute Engine
  • Amazon EC2
  • Amazon ECS
  • Rackspace
  • Microsoft Azure


50. What are the areas docker covers?

  • Simplifying configuration
  • Code Pipeline Management
  • Developer Productivity
  • Application Isolation
  • Debugging Capabilities
  • Multi-tenancy
  • Rapid Deployment


Here, this blog brings us to the end of the top 50 interview questions on docker asked by interviewers in a Docker professional interview. Wissenhive covered almost every question that can help you in gaining and updating your knowledge to the next level and help you in clearing your interview.

Are you stuck with any questions? Feel free ''Learners'' to mention it down in the comment section, and we will get back to you as soon as possible.

If you find this docker interview questions and answers blog useful then, you can start learning docker software or enhance your skills from industry professionals by enrolling yourself in our docker certification training.



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