Day 21 Task: Docker Important interview Questions.

1. What is the difference between an Image, Container, and Engine?

• Image: An image is a lightweight, standalone, and executable software package that includes everything needed to run a piece of software, including the code, runtime, system tools, libraries, and settings.

• Container: A container is an instance of a Docker image that runs in isolation on a host system. It encapsulates the application and its dependencies while sharing the host system's kernel. Containers are portable, consistent, and efficient.

• Engine: The Docker Engine is a client-server application that provides the necessary tools for managing and running Docker containers. It includes a daemon, REST API, and a command-line interface (CLI).

2. What is the difference between the Docker command COPY vs ADD?

• Both COPY and ADD commands in a Dockerfile are used to copy files from the host system into the container.

• COPY: This command copies files and directories from the host to the container. It is straightforward and is recommended for most use cases.

• ADD: In addition to copying files, ADD can also handle URLs and automatically extract compressed files. However, it is more complex and can lead to unexpected behavior if used improperly.

3. What is the difference between the Docker command CMD vs RUN?

• CMD: This instruction specifies the default command to run when a container is started from an image. It can be overridden during container runtime.

• RUN: This instruction is used to execute commands during the image build process. It is commonly used for installing dependencies, setting up the environment, and other build-time tasks.

4. How Will you reduce the size of the Docker image?

• Use a smaller base image.

• Minimize the number of layers in your image.

• Combine multiple RUN commands into a single layer.

• Avoid unnecessary packages and dependencies.

• Clean up temporary files and caches after installing software.

• Use multi-stage builds to create smaller final images.

• Use Docker's build context exclusion to limit the files included in the build.

5. Why and when to use Docker?

• Docker is used to achieve consistency and portability in software deployment. It allows you to package applications and their dependencies into containers, ensuring that they run consistently across different environments. Docker is useful for microservices architecture, DevOps practices, and simplifying the development-to-production workflow.

6. Explain the Docker components and how they interact with each other.

• Docker Engine: The core component responsible for managing containers.

• Docker Image: A lightweight, executable software package containing the application and its dependencies.

• Docker Container: An instance of a Docker image running in isolation.

• Docker Compose: A tool for defining and running multi-container applications.

• Docker Registry: A repository for storing and sharing Docker images.

• Dockerfile: A script that defines how to build a Docker image.

7. Explain the terminology: Docker Compose, Docker File, Docker Image, Docker Container?

• Docker Compose: A tool for defining and running multi-container Docker applications using a YAML file.

• Docker File: A text file containing instructions for building a Docker image.

• Docker Image: A package containing an application and its dependencies.

• Docker Container: An instance of a Docker image running in isolation.

8. In what real scenarios have you used Docker?

• Share your personal experience and real-world scenarios where you've used Docker to develop, test, or deploy applications. Focus on the challenges you faced and how Docker helped you overcome them.

9. Docker vs Hypervisor?

• Docker: Uses containerization to run applications in isolated environments, sharing the host OS kernel. It is more lightweight, efficient, and offers faster startup times.

• Hypervisor: Creates virtual machines (VMs) that run complete OS instances. It is less efficient due to the overhead of managing multiple operating systems.

10. What are the advantages and disadvantages of using Docker?

• Advantages: Portability, Consistency, Isolation, Efficiency, Rapid scaling, Version control.

• Disadvantages: Complexity for certain applications, Security concerns in multi-tenant environments.

11. What is a Docker namespace?

• A Docker namespace is a mechanism that isolates and separates resources within a container, providing each container with its own view of system resources like process IDs, network interfaces, and filesystem mounts.

12. What is a Docker registry?

• A Docker registry is a repository for storing and sharing Docker images. It allows you to distribute and manage container images, making them accessible to users across different systems.

13. What is an entry point?

• An entry point is a command that is executed when a Docker container starts from an image. It defines the default behavior of the container and can be overridden at runtime.

14. How to implement CI/CD in Docker?

• Set up a CI/CD pipeline that includes steps for building Docker images, running tests, pushing images to a registry, and deploying containers to production using tools like Jenkins, GitLab CI/CD, or GitHub Actions.

15. Will data on the container be lost when the Docker container exits?

• Yes, by default, data stored in a container's ephemeral filesystem is lost when the container exits. To persist data, you can use Docker volumes or bind mounts.

16. What is a Docker swarm?

• Docker Swarm is Docker's native orchestration solution for managing and scaling containerized applications across a cluster of machines. It allows you to create and manage a swarm of Docker nodes to distribute and run containers.

17. Docker commands:

• View running containers: docker ps

• Run a container under a specific name: docker run --name <container_name> <image>

• Export a Docker container: docker export <container_id> > container.tar

• Import an existing Docker image: docker import container.tar <image_name>

• Delete a container: docker rm <container_id>

• Remove all stopped containers, unused networks, build caches, and dangling images: docker system prune -a

18. Common Docker practices to reduce image size:

• Use a smaller base image.

• Minimize the number of layers.

• Combine commands to reduce layers.

• Remove unnecessary files and dependencies.

• Optimize image caching.

• Use multi-stage builds.

• Utilize .dockerignore to exclude unnecessary files.

These answers should help you prepare for your interview and provide a solid understanding of Docker concepts and practices.

Happy Learning :)

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