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Docker

55 Docker interview questions

Only coding challenges
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Docker Fundamentals


  • 1.

    What is Docker, and how is it different from virtual machines?

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  • 2.

    Can you explain what a Docker image is?

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  • 3.

    How does a Docker container differ from a Docker image?

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  • 4.

    What is the Docker Hub, and what is it used for?

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  • 5.

    Explain the Dockerfile and its significance in Docker.

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  • 6.

    How does Docker use layers to build images?

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  • 7.

    What’s the difference between the COPY and ADD commands in a Dockerfile?

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  • 8.

    What’s the purpose of the .dockerignore file?

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  • 9.

    How would you go about creating a Docker image from an existing container?

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  • 10.

    In practice, how do you reduce the size of Docker images?

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  • 11.

    What command is used to run a Docker container from an image?

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  • 12.

    Can you explain what a Docker namespace is and its benefits?

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  • 13.

    What is a Docker volume, and when would you use it?

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  • 14.

    Explain the use and significance of the docker-compose tool.

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  • 15.

    Can Docker containers running on the same host communicate with each other by default? If so, how?

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Docker Networking


  • 16.

    Describe the different types of networks in Docker.

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  • 17.

    How do you create a Docker network?

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  • 18.

    How could you connect a container to a specific network?

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  • 19.

    Can you explain how Docker’s default bridge network differs from a user-defined bridge network?

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  • 20.

    How would you enable communication between Docker containers on different hosts?

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Docker Performance & Security


  • 21.

    How can resource constraints be applied to containers in Docker?

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  • 22.

    What are Docker security profiles, and how do they work?

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  • 23.

    Explain how you would scan a Docker image for vulnerabilities.

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  • 24.

    What is the purpose of a Docker Healthcheck?

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  • 25.

    Describe how you would handle sensitive data with Docker.

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Docker Orchestration


  • 26.

    What is Docker Swarm, and when would you use it?

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  • 27.

    Can you explain the difference between Docker Swarm and Kubernetes?

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  • 28.

    What is a Docker Stack?

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  • 29.

    How do you deploy an application stack in Docker Swarm?

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  • 30.

    How does Docker manage service replication and load balancing?

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Docker CLI & API


  • 31.

    What command would you use to list all running containers?

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  • 32.

    How can you stop all containers running on a host using a single command?

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  • 33.

    Can you describe how you would execute a command inside a running container?

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  • 34.

    What command would you use to display the logs of a container?

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  • 35.

    Explain how to copy files from a container to the local file system.

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  • 36.

    How can you inspect the details of a specific container via the CLI?

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  • 37.

    Describe how to use Docker’s REST API to start a container.

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Docker Best Practices


  • 38.

    Explain the importance of minimizing the number of layers in a Dockerfile.

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  • 39.

    Discuss the best practices for tagging Docker images.

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  • 40.

    When should you use a .dockerignore file?

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  • 41.

    Why is it advised to run only one process per container?

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  • 42.

    How should you handle logging in Docker containers?

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Docker Troubleshooting & Optimization


  • 43.

    How would you diagnose high CPU or memory usage in a container?

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  • 44.

    What steps would you take if a container consistently fails shortly after starting?

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  • 45.

    In what scenarios would you prune Docker objects, and how?

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  • 46.

    How can you monitor the performance of Docker containers?

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  • 47.

    What common issues might arise when working with Docker in a CI/CD pipeline?

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Docker Deployment & Integration


  • 48.

    How do you define a multi-container application with docker-compose?

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  • 49.

    What considerations must be made when deploying Docker containers in a production environment?

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  • 50.

    Explain the process of integrating Docker with a continuous integration system.

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  • 51.

    How would you migrate a traditional on-premise application to a Dockerized environment?

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  • 52.

    Describe how to automate the deployment of Docker containers using a CI/CD pipeline.

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Docker Storage & Persistence


  • 53.

    When would you use a bind mount over a volume?

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  • 54.

    How do you create a Docker volume, and what is its lifecycle?

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  • 55.

    What strategies would you use for data persistence in Docker clusters?

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