Question 1

What is Docker and what problem does it solve?

Accepted Answer

Docker is a containerization platform that packages applications with dependencies into isolated containers. It solves the 'works on my machine' problem by ensuring consistent environments across development, testing, and production.

Question 2

What is the difference between a Docker image and container?

Accepted Answer

An image is a read-only template containing application code, runtime, libraries, and dependencies. A container is a running instance of an image - you can create multiple containers from the same image, like objects from a class.

Question 3

What is the difference between Docker containers and virtual machines?

Accepted Answer

Containers share the host OS kernel and virtualize at the application layer, making them lightweight (start in seconds). VMs include a full guest OS and virtualize at the hardware layer, making them heavier but providing stronger isolation.

Question 4

What is a Dockerfile and what is it used for?

Accepted Answer

A Dockerfile is a text file with instructions for building Docker images. Each instruction creates a layer in the image. Common instructions include FROM, RUN, COPY, WORKDIR, EXPOSE, and CMD.

Question 5

What is the difference between CMD and ENTRYPOINT in a Dockerfile?

Accepted Answer

CMD provides default arguments that can be overridden at runtime. ENTRYPOINT defines the main executable that always runs. Use ENTRYPOINT for the command and CMD for default arguments that users can override.

Question 6

What are Docker volumes and why are they important?

Accepted Answer

Volumes are the preferred way to persist data generated by containers. They're managed by Docker, exist outside the container lifecycle, and allow data sharing between containers. Without volumes, data is lost when containers are removed.

Question 7

What is Docker Compose and when should you use it?

Accepted Answer

Docker Compose is a tool for defining and running multi-container applications using YAML files. Use it when your application needs multiple services (app, database, cache) that need to communicate and be managed together.

Question 8

What is a multi-stage build in Docker?

Accepted Answer

Multi-stage builds use multiple FROM instructions to create separate stages. Build tools and dependencies stay in earlier stages while only runtime artifacts are copied to the final minimal image, dramatically reducing image size.

Question 9

How do Docker image layers work?

Accepted Answer

Each Dockerfile instruction creates a read-only layer. Layers are cached and reused across images that share the same base. When running containers, Docker adds a writable layer on top. This enables efficient storage and faster builds.

Question 10

What is Docker Hub?

Accepted Answer

Docker Hub is the default public registry for Docker images. It hosts official images (nginx, postgres, node) and community images. You can also push your own images to share with others or use private repositories.

Question 11

Why should you avoid using the 'latest' tag in production?

Accepted Answer

The 'latest' tag is mutable and doesn't guarantee the newest version. Using it makes deployments non-reproducible and breaks rollback strategies. Always use specific version tags for production to ensure consistency.

Question 12

How do you reduce Docker image size?

Accepted Answer

Use smaller base images (alpine), multi-stage builds, combine RUN commands, use .dockerignore, remove package manager caches, and copy only necessary files. Smaller images deploy faster and have fewer vulnerabilities.

Question 13

What is the difference between COPY and ADD in a Dockerfile?

Accepted Answer

COPY simply copies files from host to image. ADD has extra features: auto-extracting tar archives and downloading from URLs. Best practice is to use COPY for transparency and only ADD when you need tar extraction.

Question 14

How do Docker networks work?

Accepted Answer

Docker creates virtual networks for container communication. Bridge is the default for single-host networking. Containers on the same network can communicate by name. Host network shares the host's network stack directly.

Question 15

Why should containers run as non-root users?

Accepted Answer

Running as root inside containers is a security risk - if the container is compromised, attackers have root access. Create a non-root user with USER instruction and run your application with minimal required permissions.

Docker Fundamentals(5 questions)

What is Docker and what problems does it solve?

What is the difference between Docker containers and virtual machines?

What is a Docker image and how does it relate to a container?

What is the Docker architecture and its main components?

What are the advantages and disadvantages of using Docker?

Docker Images(6 questions)

What are Docker image layers and how do they work?

What are Docker image tags and how do you use them?

What is the latest tag and why should you avoid using it in production?

How do you reduce Docker image size?

What is the difference between alpine, slim, and full base images?

How do you scan Docker images for vulnerabilities?

Dockerfile(10 questions)

What is a Dockerfile and what is its purpose?

What is the difference between RUN, CMD, and ENTRYPOINT?

What is the difference between ADD and COPY instructions?

How do you use ARG and ENV instructions and what is the difference?

What is a multi-stage build and why would you use it?

What is the USER instruction and why is it important for security?

What is the HEALTHCHECK instruction and how do you use it?

What is the .dockerignore file and why is it important?

What are the best practices for writing efficient Dockerfiles?

How do you optimize layer caching in Dockerfiles?

Docker Containers(7 questions)

What is a Docker container and how does it differ from an image?

How do you create, start, stop, and remove containers?

How do you run a container in detached mode vs interactive mode?

What is the difference between docker exec and docker attach?

How do you view container logs?

What are container resource limits and how do you set them?

How do you copy files between host and container?

Docker Networking(6 questions)

What are the default Docker network drivers?

What is the difference between bridge, host, and none network modes?

How do containers communicate with each other?

What is Docker DNS and how does container name resolution work?

How do you expose container ports to the host?

What is the difference between -p and -P flags?

Docker Volumes and Storage(6 questions)

What are Docker volumes and why are they important?

What is the difference between volumes, bind mounts, and tmpfs mounts?

How do you create and manage Docker volumes?

How do you share data between containers?

Where are Docker volumes stored on the host?

How do you backup and restore Docker volumes?

Docker Compose(7 questions)

What is Docker Compose and what problems does it solve?

What is the structure of a docker-compose.yml file?

How do you define services in Docker Compose?

How do you manage dependencies between services?

How do you use environment variables in Docker Compose?

What is the difference between docker-compose down and docker-compose stop?

How do you override Compose files for different environments?

Docker Security(6 questions)

What are the security concerns when using Docker?

How do you run containers as non-root users?

What are Docker security best practices?

How do you manage secrets in Docker?

What is the difference between Docker secrets and environment variables?

What are the risks of running privileged containers?

Docker in Production(6 questions)

What are the best practices for running Docker in production?

How do you implement health checks for production containers?

What is container orchestration and why is it needed?

What is the difference between Docker Swarm and Kubernetes?

How do you handle container updates and rollbacks?

How do you implement zero-downtime deployments with Docker?

Performance and Troubleshooting(6 questions)

How do you optimize Docker container performance?

What are the best practices for reducing image size?

What is BuildKit and how does it improve builds?

How do you troubleshoot a container that won't start?

How do you clean up Docker resources (images, containers, volumes)?

What is the docker system prune command?

Docker and CI/CD(4 questions)

How do you integrate Docker with CI/CD pipelines?

What is Docker-in-Docker (DinD) and when would you use it?

How do you cache Docker layers in CI/CD?

What is the best practice for tagging images in CI/CD?