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🌻Docker Interview Questions and Answers for every Solution Architect/DevOps Engineer/SDET🌻

Question 1 — What is Docker?


Docker is an open-source containerization platform. It enables developers to package applications into containers.

Docker is a tool that is used to automate the deployment of applications in lightweight containers so that applications can work efficiently in different environments. Docker can package an application and its dependencies in a virtual container that can run on any Linux, Windows, or macOS computer.


Question 2 — Why and when do we use Docker?


Here are some reasons why and when to use Docker:

1. Isolation: Docker containers provide isolation for applications and their dependencies, making it easier to deploy and run the same application consistently across different environments.

2. Portability: Docker containers can run on any host with the Docker engine installed, making it easy to move an application between development, staging, and production environments.

3. Scalability: Docker allows you to easily scale up or down the number of containers running an application, making it easy to handle changes in load or traffic.

4. Versioning: Docker allows you to version control your application, as well as the dependencies and configuration.

5. Efficient resource usage: Docker containers use fewer resources than traditional virtual machines, making them more efficient to run on the same host.

6. Microservices: Docker makes it easier to implement and manage a microservices architecture, allowing you to break down a monolithic application into smaller, loosely-coupled services.


Question 3— How containers are different from Virtual Machines?


Containers and virtual machines are both technologies used to isolate applications and their dependencies, but they have some key differences:

1. Resource Utilization: Containers share the host operating system kernel, making them lighter and faster than VMs. VMs have a full-fledged OS and hypervisor, making them more resource-intensive.

2. Portability: Containers are designed to be portable and can run on any system with a compatible host operating system. VMs are less portable as they need a compatible hypervisor to run.

3. Security: VMs provide a higher level of security as each VM has its own operating system and can be isolated from the host and other VMs. Containers provide less isolation, as they share the host operating system.

4. Management: Managing containers is typically easier than managing VMs, as containers are designed to be lightweight and fast-moving.


Question 4— What is Docker Life Cycle?



There are three important things,

  1. docker build -> builds docker images from Dockerfile

  2. docker run -> runs container from docker images

  3. docker push -> push the container image to public/private registries to share the docker images.




Question 5—What is the difference between an Image, Container, and Engine?

An image in Docker is a lightweight, stand-alone, executable package that includes everything needed to run a piece of software, including the code, a runtime, libraries, environment variables, and config files. A container is a running instance of an image. It is a lightweight, standalone, and executable software package that includes everything needed to run the software in an isolated environment. A Docker engine is a background service that manages and runs Docker containers. It is responsible for creating, starting, stopping, and deleting containers, as well as managing their networking and storage. The Docker engine is the underlying technology that runs and manages the containers.

Question 6— What is the difference between the Docker command COPY vs ADD?

The COPY command is used to copy local files from the host machine to the Docker image. It only copies the files, and does not support any other functions such as decompressing files or fetching files from a remote location. The ADD command, on the other hand, supports additional functionality beyond just copying files. In addition to copying local files, ADD also supports fetching files from a remote URL, and automatically decompressing files that are archived in a supported format (such as tar or gzip).

Question 7— What is the difference between the Docker command CMD vs RUN?

The CMD and RUN commands in Docker are used to specify commands that should be executed when a container is started from a given image. The CMD command, is used to specify the default command that should be executed when a container is started from an image. This command can be overridden when starting a container, which means that it does not have to be executed every time a container is started. The RUN command, on the other hand, is used to execute a command during the image-building process. It will run command(s) in a new layer on top of the current image and commit the results. The command(s) in a RUN instruction will always be executed when the image is being built.

Question 8— How Will you reduce the size of the Docker image?

Using the official node alpine image as a base image, is a simple solution to reduce the overall size of the image, because even the base alpine image is a lot smaller compared to the base ubuntu image.

Question 9— Why and when to use Docker?

Docker is a containerization platform that allows you to package, deploy, and run applications in a container. It provides a way to isolate an application and its dependencies from the underlying host system, making it easier to deploy and run the same application consistently across different environments. Here are some reasons why and when to use Docker: 1. Isolation: Docker containers provide isolation for applications and their dependencies, making it easier to deploy and run the same application consistently across different environments. 2. Portability: Docker containers can run on any host with the Docker engine installed, making it easy to move an application between development, staging, and production environments. 3. Scalability: Docker allows you to easily scale up or down the number of containers running an application, making it easy to handle changes in load or traffic. 4. Versioning: Docker allows you to version control your application and the dependencies and configuration. 5. Efficient resource usage: Docker containers use fewer resources than traditional virtual machines, making them more efficient to run on the same host. 6. Microservices: Docker makes it easier to implement and manage a microservices architecture, allowing you to break down a monolithic application into smaller, loosely-coupled services.

Question 10— Explain the Docker components and how they interact with each other.

Docker has several components that work together to provide a platform for packaging, deploying, and running applications in containers. These components include: 1. Docker Engine: The Docker Engine is the underlying technology that runs and manages the containers. It is responsible for creating, starting, stopping, and deleting containers, as well as managing their networking and storage. 2. Docker Daemon: The Docker Daemon is the background service that communicates with the Docker Engine. It receives commands from the Docker CLI and performs the corresponding actions on the Docker Engine. 3. Docker CLI: The Docker Command Line Interface (CLI) is a command-line tool that allows users to interact with the Docker Daemon to create, start, stop, and delete containers, as well as manage images, networks, and volumes. 4. Docker Registries: A Docker Registry is a place where images are stored and can be accessed by the Docker Daemon. Docker Hub is the default public registry, but you can also use private registries like those provided by Google or AWS. 5. Docker Images: A Docker Image is a lightweight, stand-alone, executable package that includes everything needed to run a piece of software, including the code, a runtime, libraries, environment variables, and config files. 6. Docker Containers: A Docker Container is a running instance of an image. It is a lightweight, standalone, and executable software package that includes everything needed to run the software in an isolated environment.

Question 11 — Explain the terminology: Docker Compose, Docker File, Docker Image, Docker Container?

1. Docker Compose: Docker Compose is a tool for defining and running multi-container applications. It allows you to define the services that make up your application in a single docker- compose.yml file, and then start, stop, and manage those services with a single command. 2. Dockerfile: A Dockerfile is a script that contains instructions for building a Docker image. It specifies the base image to use, any additional software to install, and any configuration files or environment variables that need to be set. 3. Docker Image: A Docker image is a lightweight, stand-alone, executable package that includes everything needed to run a piece of software, including the code, a runtime, libraries, environment variables, and config files. 4. Docker Container: A Docker container is a running instance of an image. It is a lightweight, standalone, and executable software package that includes everything needed to run the software in an isolated environment. Each container runs in its own namespace and has its own set of processes and network interfaces.

Question 12— In what real scenarios have you used Docker? Examples of scenarios where Docker can be used: 1. Developing and testing applications: Docker can be used to set up a consistent development environment for an application, including all of the dependencies and runtime environments. This makes it easy to test an application on different operating systems or configurations. 2. Deploying applications in production: Docker allows you to package an application and its dependencies in a container, making it easy to deploy the same application consistently across different environments. This can be especially useful when deploying to cloud environments, where resources are shared among multiple tenants. 3. Building and deploying microservices: Docker can be used to implement a microservices architecture, allowing you to break down a monolithic application into smaller, loosely-coupled services. This can make it easier to scale and update individual components of an application. 4. Continuous integration and delivery: Docker can be used as part of a continuous integration and delivery (CI/CD) pipeline, allowing developers to automatically build and test their code in a containerized environment. 5. Automated testing: Docker can be used to set up automated testing environments by spinning up multiple containers for different versions of dependencies, database and other services. 6. Serverless architecture: Docker can be used to package a function

Question 13 — What is a Docker namespace?

A Docker namespace is a feature of the Linux kernel that allows for the isolation of resources, such as network, process, and file system, among different groups of users and processes. Docker uses namespaces to provide isolation between containers running on the same host. When a container is created, the Docker daemon creates a new namespace for the container’s processes. This namespace is used to isolate the container’s resources, such as network interfaces, file systems, and process IDs, from the host and other containers.

Question 14— What is a Docker registry?

A Docker registry is a service that stores and distributes Docker images, and it allows users to upload, download, and manage their own images. It can be either public or private, and it can support different authentication and authorization mechanisms to control access to the images.

Question 15 — What is an entry point?

An entry point in Docker is a command or script that is executed when a container is started from an image. It’s defined in the image’s Dockerfile using the ENTRYPOINT command, and it’s used to specify the default command that should be run when a container is created from the image. It can be overridden when starting a container using the — entrypoint option.

Question 16 — How to implement CI/CD in Docker?

CI/CD (Continuous Integration/Continuous Deployment) in Docker can be implemented by following these steps: 1. Build: Use a continuous integration tool, such as Jenkins, Travis CI or CircleCI, to automatically build a Docker image from the source code whenever there are changes to the codebase. This can be done by using a Dockerfile to define the image and using the CI tool to run the docker build command. 2. Test: Run automated tests on the built image to ensure that the application is functioning correctly. This can be done by starting a container from the image and running the tests inside the container. 3. Push: Push the built image to a Docker registry, such as Docker Hub, so that it can be easily accessed by the deployment environment. 4. Deploy: Use a continuous deployment tool, such as Kubernetes or Docker Swarm, to deploy the image to the production environment. This can be done by pulling the image from the registry and starting a container from it. 5. Monitor: Monitor the deployed containers to ensure that they are running correctly and that there are no issues with the application. This can be done by using tools such as Prometheus or Elasticsearch, Logstash and others.

Question 17 — What is a Docker swarm?

Docker Swarm is a native clustering and orchestration solution for Docker. It allows you to create and manage a cluster of Docker nodes, and deploy and scale applications on the cluster. A swarm is a group of Docker engines that are running in swarm mode and joined together. Once the engines are joined in a swarm, they can be used to deploy services. A service is a group of containers that are running a specific image and are deployed on the swarm.

Question 18 — What are the docker commands for the following:

view running containers $ docker ps

command to run the container under a specific name $ docker run —name [name] [image]

command to export a docker $ docker export [OPTIONS] CONTAINER

command to import an already existing docker image $ docker import [file_name.tar] [image_name:tag]

commands to delete a container $ docker rm [container_name]

command to remove all stopped containers, unused networks, build caches, and dangling images $ : docker system prune

Question 19 — What is the difference between Docker and a Hypervisor

Docker and hypervisors are both technologies used to create and manage virtual environments, but they work in different ways and are suited for different use cases. A Hypervisor is a software that allows multiple virtual machines (VMs) to share a single physical host. Each VM runs its own operating system and has its own resources, such as CPU, memory, and storage. Docker, on the other hand, is a containerization platform that allows you to package, deploy, and run applications in a container.



 

Refer to this Github repo for more details. https://github.com/writetoritika/Docker-Zero-to-Hero Hope these are useful and you must be feeling like a champion already. Follow me for more content. Thank you! 🙏

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