Day 21- Demystifying Docker: Essential Interview Questions and Answers  (Dec 17, 2023)

Day 21- Demystifying Docker: Essential Interview Questions and Answers (Dec 17, 2023)


Docker plays a pivotal role in DevOps, making it a crucial topic for interviews, especially for those entering the field. Let's explore key Docker interview questions and equip you with insightful answers.

1. Difference between Image, Container, and Engine


  • Image: A blueprint of a file system and parameters needed for a container, often immutable.

  • Container: A runnable instance of an image, encapsulating the application and its dependencies.

  • Engine: The core of Docker, responsible for building, running, and managing containers.

2. Docker COPY vs ADD Command


  • COPY: Copies local files into the container. Simple and efficient for straightforward file copying.

  • ADD: More powerful, as it can handle URLs and automatically unpack compressed files.

3. Docker CMD vs RUN Command


  • CMD: Specifies default commands to execute when a container starts. It can be overridden at runtime.

  • RUN: Executes commands during the image build process, altering the image itself.

4. How to Reduce the Size of the Docker Image?


  • Use a minimal base image.

  • Combine RUN commands to minimize layers.

  • Remove unnecessary dependencies and files.

  • Utilize multi-stage builds.

5. Why and When to Use Docker?


  • Why: Enables consistent, reproducible environments. Enhances scalability and resource utilization.

  • When: Ideal for microservices architecture, continuous integration, and deployments.

6. Explain Docker Components and Interaction


  • Docker Compose: Orchestrates multi-container applications.

  • Docker File: A script defining steps to create a Docker image.

  • Docker Image: A snapshot of a file system and application.

  • Docker Container: An instance of a Docker image.

7. Real Scenarios Using Docker


  • Streamlining application deployment.

  • Enabling consistent testing environments.

  • Facilitating continuous integration and delivery.

8. Docker vs Hypervisor


  • Docker: Containerization, lightweight, shares host OS kernel.

  • Hypervisor: Virtualization, heavier, each VM has a separate OS kernel.

9. Advantages and Disadvantages of Docker


  • Advantages: Portability, efficiency, scalability, isolation.

  • Disadvantages: Security concerns, limited GUI support.

10. What is a Docker Namespace?


  • Provides isolated workspaces for containers, preventing naming conflicts.

11. What is a Docker Registry?


  • Repository for Docker images, often Docker Hub or private registries.

12. What is a Docker Entry Point?


  • Specifies the default executable when a container starts.

13. How to Implement CI/CD in Docker?


  • Utilize Docker in Jenkins pipelines.

  • Automate image builds and deployments.

14. Will Data on the Container be Lost When the Docker Container Exits?


  • Data in a container's ephemeral storage is lost. Use volumes for persistent data.

15. What is a Docker Swarm?


  • Docker's native clustering and orchestration solution for managing multiple containers.

Docker Commands Quick Reference:

  • View Running Containers:
  •   docker ps
  • Run Container Under a Specific Name:

  •   docker run --name my-container
  • Export a Docker Container:

  •   docker export -o container.tar my-container
  • Import an Existing Docker Image:

  •   docker import container.tar my-image
  • Delete a Container:

  •   docker rm my-container
  • Remove All Stopped Containers, Unused Networks, Build Caches, and Dangling Images:

  •   docker system prune -af

Common Docker Practices to Reduce Image Size:

  • Use a minimal base image.

  • Combine RUN commands.

  • Remove unnecessary dependencies and files.

  • Leverage multi-stage builds.