Docker Interview Questions

Docker was presented to the world in 2013, and hit the IT business at a fast pace. Before long it ended up being a success before the finish of 2017 with 8 billion container picture downloads. Expanding need for dockers demonstrated a dramatic expansion in employment opportunity. Docker is an open-source containerization platform utilized to robotize the arrangement of any application, utilizing lightweight, convenient containers. In this article, you can go through the set of frequently asked Docker interview questions and answers in the interview panel. There will be questions for beginners, at intermediate level and of difficult level. This will help you crack the interview as the topmost industry experts curate these at HKR training. Let us have a quick review of the Docker interview questions and answers.

Docker Interview Questions for Beginners:

1. What is Docker?
Docker is a containerization platform that bundles your application and every one of its conditions together as containers in order to guarantee that your application works consistently in any climate, be it advancement, production or test. Docker containers enclose a bit of software by a total file system which includes all that is expected to run: runtime, code, system apparatuses, system libraries, and so on. It coordinates fundamentally whatever which could be introduced on a server. This ensures that the software will consistently function the same, paying little heed to its current circumstance. 

2. Define Docker Images.
The Docker image aids to make Docker containers. You could make the Docker image using the built command. Because of this, it makes a container which begins when it starts to function. Each docker image is put away in the Docker registry. 

3. Command to run the image as a container
$ sudo docker run -i -t alpine /bin/bash

4. Define Docker Container.
Docker containers incorporate the application and the entirety of its conditions. It imparts the kernel to different compartments, running as segregated cycles in client space on the host operating framework. Docker containers are not attached to a particular foundation. They function on any PC, on any framework, and in any cloud. Docker containers are fundamentally runtime occurrences of Docker pictures.

5. Command to see all running container in Docker
$ docker ps

6. Command to stop the docker container
$ sudo docker stop container name

7. Define Docker Engine.
Docker engine or Docker daemon indicates the server. The docker daemon and the customers ought to be run on the equivalent or far off host, that can impart through command line customer binary and full RESTful API. 

8. Where do we store the docker volumes?
You require to navigate : /var/lib/docker/volumes

9. Most common instruction in Dockerfile.

10. Explain the states of Docker containers.
The main states of Docker container are:

  • Running
  • Paused
  • Restarting
  • Exiting

11. Define Docker Machine.
Docker machine is an instrument which allows you to introduce Docker Engine on virtual hosts. These hosts would now be able to be handled utilizing the docker-machine commands. Docker machine likewise allows you to arrange Docker Swarm Clusters. 

12. What are used to monitor the docker in production environs?
Docker Events and Docker states are used to check docker in the production environs.

13. What are Docker object labels?
Docker object labels is a strategy for applying metadata to docker objects containing, containers, pictures, volumes, swam nodes, administrations and network. 

14. Command to check Docker Client and Docker Server version.
$ docker version

15. How to interact between Docker client and Docker Daemon?
This happens using the socket.IO, Rest API, and TCP.

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Docker Interview Questions for Intermediate:

1. Important features of Docker.

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

2. Disadvantages of Docker.

  • Doesn't give a capacity alternative. 
  • Provides a helpless checking choice. 
  • No programmed rescheduling of inert Nodes. 
  • Convoluted automatic level scaling set up.

3. Advantages of Docker container

  • Provides a productive and simple introductory set up. 
  • Permits you to portray your application lifecycle in detail.
  • Easy configuration and connects with Docker Compose. 
  • Documentation gives all of the data. 

4. What is Docker Compose?
Docker Compose is a YAML document that includes insights concerning the administrations, organizations, and volumes for building the Docker application. Along these lines, you can utilize Docker Compose to make separate compartments, host them and use them to converse with one another. Every container will uncover a port for conversing with different containers. 

5. Command to login into docker repository.
$ docker login

You'll be asked to enter your username and password, and you could login easily.

6. What are Registries?
Docker hub is also called Docker's public registry, which permits you to store pictures secretly. In Docker hub, you can store a large number of pictures. There are two kinds of registry is

  • Public Registry
  • Private Registry

7. Explain Hypervisor
A hypervisor is likewise called Virtual Machine Monitor. It is a software which makes virtualization conceivable. It isolates the host framework and distributes the assets to each partitioned virtual climate. You can fundamentally have different OS on a solitary host framework. There are two kinds of Hypervisors: 

  • Native Hypervisor or Bare metal Hypervisor runs straightforwardly on the fundamental host framework. It has direct admittance to your host's framework hardware and subsequently doesn't need a base server operating framework. 
  • It's likewise called Hosted Hypervisor. This sort of hypervisor utilizes the fundamental host operating system. 

8. Define Docker Namespace
A namespace is one of the Linux highlights and a significant idea of containers. Namespace includes a layer of disengagement in containers. Docker gives different namespaces to remain versatile and not influence the hidden host framework. Few namespace types upheld by Docker are Mount, PID, User, Network, IPC.

9. Explain Docker hub
Docker images make docker containers. There must be a registry where those docker images live. This registry is Docker Hub. Clients can get pictures from Docker Hub and use them to make customized pictures and containers. Right now, the Docker Hub is the world's biggest public repository of picture containers. 

10. What is Docker Swarm?
Docker Swarm is a local collective for docker that encourages you to turn a team of Docker hosts into a solitary and virtual docker host. It provides the standard docker application program interface.

11. Methods to create a docker container from an image.
Drag an image from docker repository using the command and run it to make a container.  Use the following command: $ docker run -it -d

-d means the container needs to start in the detached mode. 

12. Explain Virtualization
Virtualization is the method toward making a software based, virtual adaptation of something (compute stockpiling, servers, application, and so on) These virtual forms or conditions are made from a solitary actual hardware framework. Virtualization allows you to part one system into a wide range of segments that functions like discrete, particular individual frameworks. A product called Hypervisor creates this sort of parting conceivable. The virtual climate made by the hypervisor is called Virtual Machine. 

13. Define memory-swap flag
Memory- swap is an altered flag which possibly has meaning if- memory is likewise set. Swap permits the container to compose express memory necessities to disk when the compartment has depleted all the RAM that is accessible to it.

14. List the advanced docker commands

  • Docker info: Information command
  • Docker stats: Container information
  • Docker pull: To download an image
  • Docker images: Index of images downloaded

15. When you’ve operated with an image, how will you push it to docker hub?
docker push myorg/img

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Docker Interview Questions for Experienced:

1. Explain Docker Architecture?
Docker Architecture comprises of a Docker Engine that is a customer server application with three significant segments: 

  • A server that is a kind of long-running project called a daemon process or the docker command. 
  • A REST API that indicates interfaces that projects can utilize to converse with the daemon and teach it what to perform. 
  • A command line interface (CLI) customer. 
  • The CLI utilizes the Docker REST API to command or cooperate with the Docker daemon via scripting or direct CLI orders. Numerous other Docker applications utilize the hidden API and CLI.

2. Explain Dockerfile
Docker can fabricate pictures naturally by reading the directions from a record called Dockerfile. A Dockerfile is a text report which includes all the commands a client could approach the command line to gather a picture. Utilizing docker build, clients can make a mechanized form which implements a few command line directions in progression. 

3. Explain the lifecycle of a Docker Container.
Docker containers have the given lifecycle:

  • Make a container
  • Function the container
  • Pause the container
  • Unpause the container
  • Begin the container
  • Stop the container
  • Restart the container
  • Kill the container
  • Destroy the container

4. Explain the platforms on which docker runs on?
Docker operates on different Linux administration:

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

It could also be utilized in production with Cloud platforms using the following services:

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

5. Define CNM
CNM represents the Container Networking Model. It is a norm or specification from Docker, Inc. which shapes the premise of container organizing in a Docker climate. This current docker's methodology furnishes container organizing with help for various network drivers.

6. Is there a chance for cloud to overtake the use of Containerization?
Docker containers are acquiring popularity and yet, Cloud administrations are trying a decent battle. Docker won't ever be supplanted by Cloud. Utilizing cloud administrations with containerization will surely increase publicity for the game. Associations require to take their prerequisites and conditions into thought and image and choose what's suitable for them. The greater part of the organizations have incorporated Docker with the cloud. Through this method, they can get the best out of both the advances. 

7. Comparison between Virtual Machine and Docker
Virtual Machines

  • More resources are required. 
  • Booting takes time. 
  • Operating systems are separate for every VM. 
  • Takes more time for creation of Virtual Machine. 
  • Customization is possible. 
  • Process isolation is handled at hardware level.


  • Less resources are required. 
  • Booting can be done within a fraction of seconds. 
  • Operating System assets could be shared within Docker.
  • Docker can be created fastly. 
  • Custom container method is simple. 
  • Process isolation is handled at Operating System level

8.How to identify the status of a Docker container?
There are six potential states a container can be at some random point – Created, Running, Paused, Restarting, Exit, Dead. Utilize the given command to check for docker state at some random point: 

$ docker ps

The above command records down just showing containers to default. To search for all containers, utilize the accompanying command: 

$ docker ps -a

9.What makes Docker different from other containerization technologies?
Docker containers are extremely simple to deploy in cloud platforms. It could avail more applications functioning on a similar hardware while contrasted with different innovations, it makes it simple for engineers to rapidly make, ready-to-run containerized apps and it makes handling and sending applications a lot simpler. You could even impart containers to your applications.

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10. What are the commands to stop and restart the Docker container? 
You should  stop the container first, and next remove it. The commands are:

  • $ docker stop
  • $ docker rm -f

11. How will I run multiple copies of a Compose file on the same host?
Docker compose utilizes the Project name to make one of a kind identifiers for the whole task's containers and assets. To run various duplicates of a similar venture, you should set a custom project name utilizing the – p command line alternative or you can utilize the COMPOSE_PROJECT_NAME variable for this reason. 

12. What changes can be seen in your docker compose file while moving it to production? 
These are the changes you require to make to your document prior to relocating your application to the production climate: 

  • Eliminate volume ties, so that code would be maintained inside the container and can't be altered from outside the container. 
  • Authoritative to various ports on the host. 
  • Determine a restart strategy.
  • Add additional administrations like log aggregator.

13. What is the advantage of using a Docker over a Hypervisor?
In spite of the fact that Docker and Hypervisor may do a similar function in general, there are numerous contrasts between them regarding how they operate. Docker can be considered as lightweight as it utilizes less assets and furthermore the host piece as opposed to making it like a Hypervisor.

14. Where do you think Docker is being utilized?

  • Designer Productivity: Utilising Docker for improvement provides us two things, production and advancement climate is assembled quicker. 
  • Troubleshooting Capabilities: Docker upholds different debugging apparatuses which are not explicit to containers but rather function admirably with containers. 
  • Application Isolation: As containers are applications wrapped along with all conditions, your applications are confined. They could operate without anyone else on any equipment which upholds Docker. 
  • Multi-tenancy: Docker allows you to have multi-tenant applications dodging excess in your codes and organizations. 
  • Streamlining configuration: Docker allows you to place your current circumstance and configure into code and send it. 
  • Fast Deployment: Docker takes out the requirement to promote a whole OS without any preparation, decreasing the sending time.
  • Code Pipeline Management: There are various frameworks utilized for improvement and production. As the code ventures out from advancement to testing to creation, it experiences a distinction in the climate. Docker aids in keeping up the code pipeline consistency. 

15. What number of containers can be run per host?
Based on the climate where Docker will host the containers, there could be the same number of containers  as the climate upholds. The accessible assets (like CPU, memory), application size will choose the quantity of containers which can function in a climate. In spite of the fact that containers make novel CPUs all alone yet they can give effective methods of using the assets. The containers are excessively lightweight and just keep going as long as the cycle they are operating.

Thus, by experiencing the above questions you can pick up a fundamental impression of the frequently asked Docker interview questions that you can expect in the interview panel. Aside from the Docker interview questions referenced above, you can locate a wide cluster of hotspots for nitty gritty interview questions and answers. You can utilize such sources for picking up a comprehension of each Docker interview question.

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