Docker Interview Questions: Common Topics Quiz Quiz

Challenge your understanding of key Docker concepts with this quiz, designed to help you review containerization basics, networking, storage, and orchestration. Enhance your Docker interview preparation with realistic questions focused on practical and theoretical aspects of using Docker.

1. Understanding Docker Images

   Which statement best describes the purpose of a Docker image in the containerization process?

   1. A Docker image holds only runtime logs for a container.
   2. A Docker image is a type of virtual machine snapshot.
   3. A Docker image is a read-only template used to create containers.
   4. A Docker image runs directly as a standalone executable.

   Explanation: A Docker image serves as a read-only template from which containers are instantiated, containing application code, libraries, and environment settings. Unlike a standalone executable, an image cannot be directly run; it must be used to start a container. Containers, not images, generate runtime logs. Docker images are not the same as virtual machine snapshots, as they do not contain full operating systems.

2. Container Persistence

   If you need data generated by a Docker container to persist even after the container is removed, which Docker feature should you use?

   1. Docker Layers
   2. Docker Volumes
   3. Docker Tags
   4. Docker Compose Files

   Explanation: Docker volumes are specifically designed to store persistent data independent of the container’s lifecycle. They allow information to be retained even if the container is deleted or recreated. Docker layers are part of the image build process and don't preserve data at runtime, Compose files are for orchestrating multi-container setups and do not handle persistence, and tags are used for image versioning, not data storage.

3. Docker Networking Modes

   In Docker, what is the primary purpose of the 'bridge' network mode when launching containers?

   1. To create encrypted tunnels between containers across multiple hosts
   2. To enable containers to communicate with each other on the same host using a private network
   3. To make all container ports accessible from any external network without restriction
   4. To connect containers directly to physical hardware interfaces

   Explanation: The 'bridge' network mode creates a private virtual network on the host, allowing containers to communicate securely with each other while remaining isolated from the outside unless ports are mapped. Allowing all ports to be open would pose security risks and is not the function of bridge mode. Direct hardware interface access and encrypted cross-host tunneling are provided by different configurations and are not part of the 'bridge' network’s primary purpose.

4. Dockerfile Instructions

   Which Dockerfile instruction is used to specify a command that should run by default when a container starts?

   1. EXPOSE
   2. RUN
   3. COPY
   4. CMD

   Explanation: CMD defines the default command to run when a container starts, unless overridden at runtime. RUN executes commands while building the image, not at container start. COPY is used to transfer files and directories into the image. EXPOSE is a way to document which network ports the container will listen on, but does not specify which command to execute.

5. Container Orchestration

   When managing multiple Docker containers as a group with scaling and self-healing, which concept or tool is commonly employed?

   1. Linking
   2. Tagging
   3. Orchestration
   4. Port Mapping

   Explanation: Orchestration involves coordinating and managing clusters of containers, allowing for automatic scaling, load balancing, and recovery from failures. Linking is an older method of connecting containers and does not provide group management. Tagging is used for versioning images and has no effect on container coordination. Port mapping is related to network configuration, not container management or scaling.