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Docker-Interview-questions.md

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Docker Interview based questions🚀

These questions cover advanced concepts, real-world scenarios, troubleshooting, and optimization techniques you are likely to encounter in an SRE role.

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Core Docker Concepts

  1. What is Docker, and how does it differ from Virtual Machines?
    Explain containerization vs virtualization.

  2. Can you explain the Docker architecture? What are the key components?
    Docker Engine, Docker CLI, Docker Daemon, Docker Images, Containers, and Registries.

  3. What happens when you run docker run hello-world? Explain step-by-step.

  4. What is the difference between docker run, docker start, and docker exec?

  5. What is the difference between COPY and ADD in a Dockerfile? When would you use each?

  6. What are multi-stage builds in Docker? Why are they useful for production deployments?

Docker Images and Containers

  1. How do you optimize Docker image size? Give practical steps.
    E.g., using lightweight base images like Alpine, multistage builds, removing unnecessary files, minimizing layers, etc.

  2. How can you debug a container that exits immediately after starting?

  3. What is the difference between ENTRYPOINT and CMD in a Dockerfile? Can you override them?

  4. How do you inspect the environment variables and configuration of a running container?

  5. What is the role of docker-compose? What is the difference between docker-compose up and docker-compose down?

  6. What happens if you do not specify a WORKDIR in a Dockerfile?

  7. How do you handle logs for Docker containers? What tools would you use for log aggregation?

  8. Explain how you would copy a file from a running container to the host machine.

  9. How can you reduce container startup time for a large application?

Networking

  1. What are Docker networks, and what are the different types of Docker networks?
    Bridge, host, overlay, and macvlan networks.

  2. How would you connect two containers running on different hosts?

  3. Explain the difference between port binding (-p) and exposing a port (EXPOSE) in Docker.

  4. How does Docker handle DNS resolution for containers?

  5. What happens if you use --network=host mode? What are the advantages and disadvantages?

Storage and Volumes

  1. What are Docker volumes? How do they differ from bind mounts?

  2. How would you persist data from a container?

  3. What is the difference between named volumes and anonymous volumes?

  4. How can you back up and restore Docker volumes?

Docker Security

  1. What are some security best practices you follow while working with Docker?
    E.g., using non-root users, scanning images for vulnerabilities, minimizing image size, etc.

  2. How can you restrict resource usage for a container (e.g., CPU and memory limits)?
    Use --cpus, --memory, or cgroups.

  3. How do you scan a Docker image for security vulnerabilities? What tools do you use?

  4. What is Docker Content Trust, and how does it help improve image security?

  5. Explain the concept of a Docker “rootless mode.” Why is it significant?

  6. What is the purpose of seccomp, AppArmor, or SELinux in Docker security?

Troubleshooting and Debugging

  1. How do you troubleshoot a container that keeps restarting?

  2. What steps do you take when you encounter the error OCI runtime create failed?

  3. How do you clean up unused Docker containers, volumes, and networks?

  4. Explain how to handle zombie processes inside a container.

  5. How can you check why a container is consuming too much memory or CPU?

  6. How do you monitor Docker containers in production? What tools or methods do you use?
    Prometheus, Grafana, cAdvisor, ELK stack, etc.

  7. Explain how you would recover from a corrupted Docker image or container.

  8. How do you resolve a Docker daemon not responding issue?

Docker in CI/CD and Kubernetes

  1. How do you integrate Docker into CI/CD pipelines? Which tools do you use?
    Jenkins, GitLab CI, GitHub Actions, etc.

  2. What is a Docker registry? What are the differences between Docker Hub, ECR, and private registries?

  3. How do you push and pull Docker images from a private registry?

  4. How do you ensure Docker containers restart automatically on failure?

  5. What role does Docker play in Kubernetes?

  6. How do you manage secrets in a Docker container securely?

Real-World Scenarios

  1. Imagine a containerized app works locally but fails in production. How would you debug it?

  2. How would you troubleshoot a network connectivity issue between two containers?

  3. What would you do if Docker images take too long to build during deployment?

  4. How would you migrate containers running on a Docker Engine to Kubernetes?

  5. How do you ensure zero downtime when deploying updates to a containerized application?

  6. You have a container running out of memory and crashing. What tools and steps would you use to analyze and resolve it?

Bonus Situational Questions

  1. If your Docker image builds are too large, what actions would you take to improve efficiency?

  2. You notice a resource-intensive container affecting host performance. How would you limit its resource usage immediately?

  3. A containerized application throws intermittent errors but works fine most of the time. What steps would you take to investigate this?

  4. What would you do if you accidentally deleted a Docker volume containing important data?

  5. A team member created a Dockerfile, but the container keeps crashing. How would you perform a code review to find the issue?

Tools and Utilities

  • What tools do you use for container monitoring and health checks?
  • How do you automate container cleanup in production?
  • Which tools do you prefer for Docker image vulnerability scanning?

Final Notes for Preparation

To ace these questions as an SRE, make sure you can:

  1. Explain concepts clearly.
  2. Use real-world examples or scenarios you've handled.
  3. Understand how Docker integrates with tools like Kubernetes, CI/CD, and monitoring systems.
  4. Troubleshoot and optimize effectively.

#devops