Docker Beginner Interview Questions and Answers (2025)

Are you preparing for a Docker-related interview in 2025? Whether you're a beginner or looking to refresh your knowledge, this blog covers the most common Docker interview questions along with simple, clear answers.

1. Basic Docker Questions

Q1. What is Docker?

Answer:
Docker is an open-source platform that allows developers to build, deploy, and run applications inside lightweight, portable containers. Containers package an application with all its dependencies, ensuring consistency across different environments.

Q2. What is a Docker Container?

Answer:
A Docker container is a lightweight, standalone, and executable software package that includes:

• Application code
• Runtime (e.g., Node.js, Python)
• System libraries
• Environment variables

Containers run in isolation from each other but share the host OS kernel.

Q3. What is a Docker Image?

Answer:
A Docker image is a read-only template used to create containers. It contains:

• Application code
• Dependencies
• Configuration files
• Environment settings

Images are built from a Dockerfile and stored in registries like Docker Hub.

Q4. What is the Difference Between a Docker Image and a Container?

Answer:

Example:

• Image → Like a blueprint of a house.
• Container → Like an actual house built from that blueprint.

2. Docker Commands & Operations

Q5. How Do You Run a Docker Container?

Answer:

docker run -d -p 8080:80 --name my_container nginx

• -d → Run in detached (background) mode.
• -p 8080:80 → Map host port 8080 to container port 80.
• --name → Assign a name to the container.

Q6. How Do You List Running Containers?

Answer:

docker ps

• To list all containers (including stopped ones):

  docker ps -a
  

Q7. How Do You Stop and Remove a Container?

Answer:

• Stop a container:

  docker stop container_name
  

• Remove a container:

  docker rm container_name
  

• Force remove a running container:

  docker rm -f container_name
  

Q8. How Do You Build a Docker Image?

Answer:

1. Create a Dockerfile.
2. Run:

   docker build -t my_image:1.0 .
   

   • -t → Tag the image with a name and version.
   • . → Path to the Dockerfile.

3. Docker Networking & Storage

Q9. How Does Docker Networking Work?

Answer:
Docker provides different networking modes:

• Bridge (Default) → Containers communicate via an internal network.
• Host → Containers share the host’s network directly.
• None → No networking (isolated).

Example:

docker run --network=host nginx

Q10. What is a Docker Volume?

Answer:
A Docker volume is used to persist data outside containers.

• Use Case: Databases, logs, or config files.

Commands:

• Create a volume:

  docker volume create my_volume
  

• Mount a volume in a container:

  docker run -v my_volume:/app/data nginx
  

4. Docker vs. Virtual Machines (VMs)

Q11. What’s the Difference Between Docker and a VM?

Answer:

Example:

• Docker → Like an "apartment" (shared resources).
• VM → Like a "house" (dedicated resources).

5. Advanced Beginner Questions

Q12. What is Docker Compose?

Answer:
Docker Compose is a tool for defining and running multi-container applications using a docker-compose.yml file.

Example:

version: "3.8"
services:
  web:
    image: nginx
    ports:
      - "8080:80"
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: password

Run with:

docker-compose up -d

Q13. How Do You Debug a Docker Container?

Answer:

• Check logs:

  docker logs container_name
  

• Enter a running container:

  docker exec -it container_name sh
  

Q14. What is a Dockerfile?

Answer:
A Dockerfile is a text file with instructions to build a Docker image.

Example:

FROM ubuntu:latest
RUN apt-get update && apt-get install -y python3
COPY . /app
WORKDIR /app
CMD ["python3", "app.py"]

6. Scenario-Based Questions

Q15. How Would You Deploy a Web App Using Docker?

Answer:

1. Write a Dockerfile for the app.
2. Build the image:

   docker build -t my_web_app .
   

3. Run the container:

   docker run -d -p 5000:5000 my_web_app
   

Q16. What Happens if a Container Crashes? How Do You Restart It?

Answer:

• Use --restart policies:

  docker run --restart=always nginx
  

  • no → No restart (default).
  • always → Always restart.
  • on-failure → Restart only on failure.

Conclusion

These Docker interview questions cover fundamental concepts, commands, and real-world scenarios. If you're preparing for an interview in 2025, make sure to practice these answers and experiment with Docker commands hands-on.

Good luck with your Docker interview! 🚀🐳