Top Answers to Docker Interview Questions

1. What is Docker?
CriteriaDocker Virtual Machines
Use of OSAll containers share host OSEach VM runs in its own OS
Startup timeVery fastSlow
IsolationProcess level isolationFull isolation
securityLowHigh

You can define Docker as a containerization platform that combines all your applications in a package so that you have all the dependencies to run your applications in any environment. This means your application will run seamlessly on any environment and this makes it easy for having a product ready application. What Docker does is wrap the software that is needed in a file system that has everything for running the code, providing the runtime and all the necessary libraries and system tools. Containerization technology like Docker will share the same operating system kernel with the machine and due to this it is extremely fast. This means that you have to run the Docker only at the beginning and after that since your OS is already running, you will have a smooth and seamless process.

2. What is the benefit of using a Docker over a hypervisor?

Though Docker and Hypervisor might do the same job overall there are many differences between them in terms of how they work. Docker can be thought of as light weight since it uses very less resources and also the host kernel rather than creating it like a Hypervisor.

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3. What are the unique features of Docker over other containerization technology?

Here we list some of the most important and unique features of Docker that makes it a top containerization technology unlike any other in the market today

  • You can run your Docker container either on your PC or your enterprise IT system
  • Along with the Docker Hub which is a repository of all containers you can deploy and download all your applications from a central location
  • You can even share your applications with the containers that you create.

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4. What is Docker image?

Here we will be explaining what is the Docker image. The Docker image help to create the Docker containers. You can create the Docker image with the build command, due to this it creates a container that starts when it begins to run. All the docker images are stored in the Docker registry like the public docker registry. These have minimal amounts of layers within the image so that there is minimum amount of data on the network.

5. What is Docker container?

Here we will be discussing what is a Docker container. It is a comprehensive set of applications including all its dependencies which share the same OS kernel along with the other containers running in separate processes within the operating system in a user space. The Docker is not tied to any IT infrastructure and thus it can run on any computer system or the cloud. You can create a Docker container using the Docker images and then running it or you can use the images that are already created in the Docker Hub. To simplify things, let us say that the Docker containers are just runtime instances of the Docker image.

6. What is Docker hub?

You can think of Docker Hub as a cloud registry that lets you link the code repositories, create the images and test them. You can also store your pushed images, or you can link to the Docker Cloud, so that the images can be deployed to the host. You have a centralized container image discovery resource which can be used for collaboration of your teams, automating the workflow, distribution and change management by creating the development pipeline.

7. What is Docker Swarm?

You can think of Docker Swarm as the way of orchestrating the Docker containers. You will be able to implement the Dockers in a cluster. You can convert your Docker pools into a single Docker Swarm for easy management and monitoring.

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8. What is the use of Dockerfile?

The Dockerfile can be thought of as a set of instructions that you need to pass on to the Docker so that the images can be built from the specified instructions in the Dockerfile. You can think of the Dockerfile as a text document which has all the commands that are needed for creating a Docker image. You can create an automated build that lets you execute multiple command-lines one after the other.

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9. Is it possible to use JSON instead of YAML for Docker compose?

You can use JSON instead of YAML for Docker compose file. So when you are using the JSON file for composing then you have to specify the filename with the following command:

docker-compose -f docker-compose.json up

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10. Tell us how you have used Docker in your past position?

This is a question that you could bring upon your whole experience with Docker and if you have used any other Container technologies before Docker. You could also explain the ease that this technology has brought in the automation of the development to production lifecycle management. You can also discuss about any other integrations that you might have worked along with Docker such as Puppet, Chef or even the most popular of all technologies – Jenkins. If you do not have any experience with Docker itself but similar tools from this space, you could convey the same and also show in your interest towards learning this leading containerization technology.

11. What is the process for creating a Docker container?

You can use any of the specific Docker image for creating a Docker container using the below command.

docker run -t -i command name

This command not only creates the container but also will start it for you. If you want to check if the Docker container has been created or not then you need to have the following command which will list all the Docker containers along with the host on which the Docker container runs.

docker ps -a

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12. What is the process for stopping and restarting a Docker container?

If you want to stop a Docker container then you need to use the following command:

CONTAINER_ID:

docker stop CONTAINER_ID

If you want to restart a Docker container then you need to use the following command

CONTAINER_ID:

docker restart CONTAINER_ID

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13. How do you scale your Docker containers?

The Docker containers can be scaled to any level starting from a few hundreds to even thousands or millions of containers. The only condition is that the containers need the memory and the OS at all times and there should not be a constraint on these when the Docker is getting scaled.

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