Docker Important interview Questions
What is Docker?
Docker is a software platform that allows you to create, deploy, and run applications in containers. Docker helps to simplify the process of deploying and running applications by packaging them into self-contained containers, which can be easily moved and run on different machines, regardless of their underlying infrastructure.
What is Docker Image?
An image is a read-only file that contains the instructions for creating a Docker container. It's like a blueprint for the container, specifying what operating system, libraries, dependencies, and applications will be included.
What is Docker Container?
A container is a lightweight, standalone executable package of software that includes everything needed to run an application, such as code, libraries, system tools, and settings.
What is the Difference between the Docker command COPY vs ADD?
COPY can only copy files from the host machine into the container. ADD, on the other hand, can also copy files from remote URLs, and it can automatically extract compressed files in the process.
What is the Difference between the Docker command CMD vs RUN?
RUN is used in the Dockerfile to execute commands during the build process, such as installing dependencies or setting up the environment. CMD, on the other hand, is used to specify the default command to run when the container starts.
RUN commands are executed during the build process and affect the image's layers, while CMD is executed when the container is started and doesn't affect the image's layers.
How Will you reduce the size of the Docker image?
Use a smaller base image: The base image you choose can have a significant impact on the overall size of your Docker image. Choosing a smaller base image, such as Alpine Linux, can help reduce the image size.
Use multi-stage builds: Multi-stage builds allow you to use multiple Docker images in a single Dockerfile. This can help reduce the overall size of the final image by only including the necessary files and dependencies.
Why and when to use Docker?
Here are some reasons why and when to use Docker:
Isolation: Docker containers provide isolated environments for each application, ensuring that applications run consistently across different environments.
Portability: Docker images can be easily moved between environments, allowing developers to quickly spin up new instances of an application on any platform that supports Docker.
Scalability: Docker containers can be easily scaled horizontally by adding more instances, making it simple to accommodate increased traffic or demand.
Ease of deployment: Docker containers can be deployed on any platform that supports Docker, making it easy to deploy an application consistently across different environments.
Environment consistency: Docker containers ensure that an application runs consistently across different environments, making it easier to test and deploy applications.
Explain the Docker components and how they interact with each other.
Here is a brief overview of each component and how they interact with each other:
Docker daemon: The Docker daemon is the background process that manages and controls Docker containers and images.
Docker client: The Docker client is a command-line tool that allows users to interact with the Docker daemon to build, run, and manage containers.
Docker registry: A Docker registry is a repository that stores Docker images and allows users to share and distribute them with others.
Docker network: Docker network allows containers to communicate with each other and with the host system. Each container can be connected to one or more networks.
Docker volume: Docker volume is a way to store and manage persistent data used by containers. Volumes are separate from containers and can be reused across multiple containers.
The Docker daemon runs in the background and listens for requests from the Docker client. The Docker client sends commands to the Docker daemon to build, run, and manage containers. The Docker image is used to create a Docker container, which runs as a standalone application. The Docker registry is used to store and share Docker images. Containers can communicate with each other and with the host system using Docker network, and persistent data can be managed using Docker volumes.
Explain the terminology: Docker Compose, Docker File.
Docker Compose: Docker Compose is a tool for defining and running multi-container Docker applications. It allows you to define the services, networks, and volumes for your application in a YAML file, and then start and stop the application with a single command.
Dockerfile: A Dockerfile is a text file that contains the instructions for building a Docker image. It defines the base image, adds additional layers, and sets the configuration options for the image. The Dockerfile can be used to automate the building of images and ensure that each image is consistent and reproducible.
Docker vs Hypervisor?
Hypervisors create separate virtual machines with their own operating systems, while Docker uses containers to isolate applications on a shared operating system. Hypervisors are typically used for running multiple operating systems on a single machine, while Docker is used for running multiple applications on a single operating system.
What is a Docker namespace?
In Docker, a namespace is a feature of the Linux kernel that allows for the isolation of resources between processes. Docker uses namespaces to provide a level of isolation between containers, allowing multiple containers to run on the same host without interfering with each other.
What is a Docker registry?
A Docker registry is a repository for storing and distributing Docker images. It is a centralized location for storing and distributing Docker images. The most commonly used public registry is Docker Hub, but you can also create your private registry.
What is an entry point?
An entry point is a script that is executed when a container is launched. It is used to define the commands that should be executed when the container starts. It is also used to set environment variables, configure networking, and set up logging.
How to implement CI/CD in Docker?
Implementing CI/CD in Docker involves setting up a CI system to build and test the Docker image, pushing the image to a Docker registry, and using a CD system to deploy the Docker image to a production environment. The CD system can also be configured to monitor the image and take action when it changes.
Will data on the container be lost when the docker container exits?
Yes, any data stored on a Docker container will be lost when the container is stopped or exited. It is recommended to use the volume feature of the container runtimes to keep the image separate from the data.
What is a Docker swarm?
Docker Swarm is an orchestration management tool that runs on Docker applications. It helps end-users in creating and deploying a cluster of Docker nodes.
Each node of a Docker Swarm is a Docker daemon, and all Docker daemons interact using the Docker API. Each container within the Swarm can be deployed and accessed by nodes of the same cluster.
Thank you for reading! Hope you find this article helpful.
~Kunal