Docker-2 Interview Q/A

What is Hypervisor?

A hypervisor is a software that enables virtualization, allowing multiple virtual environments to run on a single host system. There are two types of hypervisors: Type 1 (bare-metal) and Type 2 (hosted).

What is virtualization?

Virtualization is the process of creating virtual versions of hardware or software components, such as compute, storage, servers, or applications. It allows a single physical system to be divided into multiple isolated virtual environments using a hypervisor.

What is containerization?

Containerization is a method of packaging and deploying applications along with their dependencies and configuration files into a container. Containers ensure that applications run consistently across different environments. Docker and Kubernetes are popular containerization solutions.

Difference between virtualization and containerization:

Virtualization creates isolated virtual machines with their operating systems, while containerization provides isolated environments for applications that share the host OS. Containers are more lightweight and efficient compared to virtual machines.

What is Docker?

Docker is a containerization platform that packages applications and their dependencies into containers, ensuring consistent operation in various environments. It encapsulates everything needed to run an application, making it highly portable.

What is a Docker Container?

A Docker container is an instance of a Docker image that includes an application and all its dependencies. Containers share the host's kernel but run as isolated processes in user space. They are highly portable and can run on any system.

What are Docker Images?

Docker images are the source of Docker containers. They serve as templates for creating containers. When a user runs a Docker image, it creates an instance of a container. Docker images can be shared and deployed to different Docker environments.

What is Docker Hub?

Docker Hub is a registry where Docker images are stored and shared. It is the world's largest public repository of container images. Users can access Docker Hub to download images and use them to create customized containers.

Explain Docker Architecture:

Docker Architecture consists of a Docker Engine, which includes a server (daemon process), a REST API, and a command-line interface (CLI). The CLI communicates with the server using the REST API to control and interact with Docker. Docker applications also use the API and CLI for management.

What is a Dockerfile?

A Dockerfile is a text document that contains instructions for building a Docker image. It specifies the commands to be executed to assemble an image, making it possible to automate image creation and customization.

Tell us something about Docker Compose:

Docker Compose is a YAML file that defines services, networks, and volumes for a Docker application. It allows users to create and manage multiple containers, specify dependencies, and facilitate communication between containers.

What is Docker Swarm?

Docker Swarm is a native clustering solution for Docker, which turns a group of Docker hosts into a single, virtual Docker host. It allows for the scaling of containers across multiple hosts and provides high availability.

What is a Docker Namespace?

Docker uses namespaces, a Linux feature, to provide isolation between containers and the host system. Namespaces help prevent conflicts and ensure portability. Various namespace types include PID, Mount, IPC, User, and Network.

What is the lifecycle of a Docker Container?

The lifecycle of a Docker container involves several stages, including creation, running, pausing (optional), un-pausing (optional), starting, stopping, restarting, killing, and ultimately destroying the container.

What is a Docker Machine?

Docker Machine is a tool for installing Docker Engine on virtual hosts. It allows users to manage and provision Docker Swarm clusters and provides an easy way to work with Docker in various environments.

How to check for Docker Client and Docker Server versions?

Use the docker version command to retrieve information about both the Docker Client and Docker Server versions.

How do you get the number of containers running, paused, and stopped?

The docker info command provides detailed information about Docker, including the number of running, paused, and stopped containers.

If you vaguely remember the command and you'd like to confirm it, how will you get help on that particular command?

To get help on a specific Docker command, use the docker <command> --help syntax. For a list of all Docker commands, use docker --help.

How to login into the Docker repository?

Use the docker login command to log in to the Docker Hub repository. It prompts you for your username and password.

If you wish to use a base image and make modifications or personalize it, how do you do that?

To use a base image and make modifications, pull the image from Docker Hub using the docker pull <image_name> command. You can then create a container from this image and customize it.

How do you list all the running containers?

Use the docker ps command to list all the running containers. By default, it displays only running containers. To list all containers, including stopped ones, use docker ps -a.

Suppose you have 3 containers running, and you wish to access one of them. How do you access a running container?

Use the docker exec -it <container id> bash command to access a running container. It allows you to execute commands within the container.

How to start, stop, and kill a container?

Use the docker start <container_id> command to start a container, docker stop <container_id> stop a running container, and docker kill <container_id> forcefully kill a container.

Can you use a container, edit it, and update it? Also, how do you make it new and store it on the local system?

Yes, you can use a container, edit it, and update it. To create a new image from the modified container, use the docker commit <container_id> <username/imagename> command.

Once you've worked with an image, how do you push it to Docker Hub?

Use the docker push <username/image name> command to push an image to Docker Hub.

How to delete a stopped container?

To delete a stopped container, use the docker rm <container id> command.

How to delete an image from the local storage system?

Use the docker rmi <image-id> command to delete an image from the local system.

How to build a Dockerfile?

To build a Dockerfile and create an image, use the docker build <path to Dockerfile> command.

Do you know why docker system prune is used? What does it do?

docker system prune is used to remove stopped containers, unused networks, dangling images, and build caches. It helps clean up the Docker environment.

Do Docker containers scale automatically?

No, Docker containers do not scale automatically. Container scaling must be managed using tools like Docker Compose, Docker Swarm, or Kubernetes.

Will you lose your data when a Docker container exits?

No, data within a Docker container is preserved even when the container exits, provided you do not explicitly delete the container. The file system within the container persists.

Where do you think Docker is being used?

Docker is used in various areas, including simplifying configuration, code pipeline management, developer productivity, application isolation, debugging, multi-tenancy, and rapid deployment.

How is Docker different from other containerization methods
Docker offers easy deployment, portability, and efficiency when compared to other containerization methods. It enables faster application creation, management, and sharing of containers.

Can I use JSON instead of YAML for my compose file in Docker?

Yes, you can use JSON instead of YAML for Docker Compose files by specifying the JSON filename using the -f flag.

How have you used Docker in your previous position?

Describe how you've used Docker to facilitate rapid deployment, integrate it with other tools like Puppet, Chef, or Jenkins, or compare it with other similar technologies if you have no previous Docker experience.

How far do Docker containers scale? Are there any requirements for the same?

Docker containers can scale to a large number, but scaling is limited by hardware resources, the host's OS, and application size. Proper resource management is essential for effective scaling.

What platforms does Docker run on?

Docker runs on various Linux distributions and is supported by cloud platforms such as Amazon EC2, Google Compute Engine, Microsoft Azure, and Rackspace.

Is there a way to identify the status of a Docker container?

Docker containers can have various statuses, including Created, Running, Paused, Restarting, Exited, and Dead. Use the docker ps command to check the status of running containers.

Can you remove a paused container from Docker?

No, you cannot remove a paused container. A container must be in the stopped state before it can be removed.

Can a container restart by itself?

Containers do not automatically restart by themselves. The restart behavior can be configured using the -restart flag.

Is it better to directly remove the container using the rm command or stop the container followed by remove the container?

It is recommended to stop a container before removing it using the docker stop and docker rm commands. This allows containers to clean up tasks gracefully.

Will cloud overtake the use of Containerization?

Containerization and cloud services can complement each other. While cloud services offer infrastructure flexibility, containerization, like Docker, enhances application deployment and management. The choice depends on the specific needs of organizations.

How many containers can run per host?

There is no strict limit to the number of containers that can run on a host. However, practical constraints include available hardware resources and the host's OS.

Is it a good practice to run stateful applications on Docker?

Running stateful applications on Docker can be challenging because data stored on the local file system may not be portable. It is not considered a best practice.

Will Docker Compose wait for the current container to be ready to move to the running of the next service?

Yes, Docker Compose follows dependencies specified in the Compose file and ensures that services are started in the correct order, waiting for dependencies to be ready before proceeding.

How will you monitor Docker in production?

Docker provides tools like docker stats and docker events for monitoring containers in production. docker stats offers insights into CPU and memory usage, while docker events providing information about Docker daemon activities.

Is it a good practice to run Docker Compose in production?

Yes, running Docker Compose in production is a common and practical application. Compose files can be used throughout the software development lifecycle, from development and testing to production.

What changes are expected in your Docker Compose file while moving it to production?

When moving a Docker Compose file to a production environment, you should consider removing volume bindings, specifying different ports on the host, setting a restart policy, and adding extra services like log aggregators.

Have you used Kubernetes? Which one would you prefer between Docker and Kubernetes?

Be honest about your experience. Compare Docker Swarm and Kubernetes, highlighting the strengths and weaknesses of each based on your experience.

Are you aware of load balancing across containers and hosts? How does it work?

Load balancing is used to distribute incoming traffic across multiple containers and hosts. It ensures high availability and performance. HAProxy and other load-balancing solutions route traffic to healthy containers, making applications more resilient.