24 questions that come up in Docker technical interviews, each with the answer and an explanation of why it is right.
Test yourself — 90 question bankAnswer: A persistent data storage mechanism
Docker volumes are the preferred mechanism for persisting data generated and used by Docker containers. They are managed by Docker and exist outside the container lifecycle.
Answer: Containerization
Docker is a platform for developing, shipping, and running applications inside lightweight, portable containers that package code and dependencies together.
Answer: Native clustering and orchestration for Docker
Docker Swarm is Docker native clustering and orchestration solution that turns multiple Docker hosts into a single virtual host.
Answer: Swarm is simpler, Kubernetes is more feature-rich
Docker Swarm is easier to set up and use but less feature-rich. Kubernetes is more complex but offers more advanced orchestration, scaling, and ecosystem.
Answer: Volumes are managed by Docker, bind mounts link to host filesystem
Volumes are stored in Docker-managed space and are isolated from host. Bind mounts directly map host filesystem paths into containers.
Answer: Definition of tasks to run on worker nodes
A service is the definition of tasks to execute on manager or worker nodes. It defines the container image, replicas, ports, and other configurations.
Answer: Defining and running multi-container applications
Docker Compose is a tool for defining and running multi-container Docker applications using a YAML file to configure services, networks, and volumes.
Answer: A read-only template for creating containers
A Docker image is a lightweight, standalone, immutable file that contains everything needed to run an application, including code, runtime, libraries, and dependencies.
Answer: To securely store and manage sensitive data
Docker secrets securely store and manage sensitive data like passwords, tokens, and keys in Swarm mode. Secrets are encrypted in transit and at rest.
Answer: docker swarm init
`docker swarm init` initializes a swarm, making the current node a manager. It returns a join token for adding worker nodes.
Answer: docker-compose.yml
`docker-compose.yml` is a YAML file that defines services, networks, and volumes for multi-container Docker applications.
Answer: A group of interrelated services in Swarm
A stack is a group of interrelated services that share dependencies and can be orchestrated together in Swarm mode. Defined using docker-compose.yml v3+.
Answer: Using multiple FROM statements to reduce final image size
Multi-stage builds use multiple FROM statements in a Dockerfile. This allows building in one stage and copying only necessary artifacts to the final stage, reducing image size.
Answer: bridge
Bridge is the default network driver. It creates a private internal network on the host where containers can communicate.
Answer: Creates and starts a new container from an image
`docker run` creates a new container from a specified image and starts it. It combines `docker create` and `docker start`.
Answer: To verify integrity and publisher of images
Docker Content Trust uses digital signatures to verify the integrity and publisher of Docker images, preventing tampering and ensuring authenticity.
Answer: All of the above
All three commands work: `docker --version`, `docker version`, and `docker -v`. The `docker version` command provides more detailed information.
Answer: To return detailed information about Docker objects
`docker inspect` returns low-level information about Docker objects (containers, images, volumes, networks) in JSON format.
Answer: To store non-sensitive configuration data
Docker configs allow storing non-sensitive configuration data outside container images in Swarm mode. Similar to secrets but for non-sensitive data.
Answer: docker stop
`docker stop` gracefully stops a container by sending SIGTERM, then SIGKILL after a grace period. `docker kill` sends SIGKILL immediately.
Answer: Overlay network for service discovery and load balancing
The ingress network is a special overlay network that provides load balancing for swarm services. All nodes participate in routing mesh.
Answer: All of the above
Environment variables can be passed using -e flag, --env-file for multiple variables from a file, or environment section in docker-compose.yml.
Answer: Load balancing feature that routes requests to available tasks
Routing mesh enables all swarm nodes to accept connections on published ports, automatically routing to available service tasks.
Answer: All of the above
Placement constraints control which nodes run service tasks. Can use node attributes (role, labels, hostname) with constraint syntax in service definitions.
The full Docker bank has 90 questions across 3 difficulty levels — timed, shuffled, and scored.
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