27 Top Docker Docker Interview Questions and Answers (2024)

Blog / 27 Top Docker Docker Interview Questions and Answers (2024)

13 billion.

What's that number you're asking?

That's the number of Docker image downloads per month in 2022.

Docker has quickly gone from a nice to know to a need to know for most tech interviews.

This blog will bring you up to speed on the latest Docker interview questions and help you nail your next tech interview.

Q1.

What is Docker?

Junior

Docker is a platform for developing, shipping, and running applications inside containers. Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package.
This ensures that the application will run on any other Linux machine regardless of any customized settings that machine might have that could differ from the machine used for writing and testing the code.

Q2.

What is containerization?

Junior

Containerization is a technology that encapsulates an application and its dependencies into a 'container'. This allows the application to run consistently across different computing environments.

Q3.

What is a hypervisor?

Junior

A hypervisor is software that creates and runs virtual machines (VMs). It allows multiple VMs, each with their own operating system, to share a single physical host's hardware resources.
There are two types:
- Type 1 (bare-metal): runs directly on the host's hardware.
- Type 2 (hosted): runs on a conventional operating system.
Hypervisors are essential in virtualization, enabling efficient resource utilization and isolation between different VMs.

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Q4.

Explain the differences between containerization and virtualization.

Junior

Containerization involves packaging applications with their dependencies in containers, sharing the host's OS kernel. It's lightweight, offers quick startup, and efficient resource use. Ideal for consistent deployment environments.
Virtualization creates full virtual machines with separate OS instances on a hypervisor. It's resource-intensive but provides stronger isolation and security. Suitable for running different OSs and applications needing full isolation.

Q5.

Explain the main components of Docker architecture.

Junior

Docker Daemon: The background service running on the host that manages building, running, and distributing Docker containers.
Docker Client: The command-line interface that allows users to interact with the Docker Daemon.
Docker Images: Read-only templates used to build containers.
Docker Containers: Runnable instances of Docker images.
Docker Registries: Storage and distribution systems for Docker images, with Docker Hub being the most common public registry.

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Q6.

Name some advantages of using Docker.

Junior

Portability: Containers run consistently across different environments.
Efficiency: Lightweight compared to virtual machines, saving system resources.
Isolation: Containers are isolated, reducing conflicts between applications.
Scalability: Easy to scale and distribute containerized applications.
Rapid Deployment: Quick to build and deploy applications.
Version Control and Reusability: Facilitates version control and reuse of container images.
Simplified Configuration: Simplifies the setup and configuration of applications.

Q7.

Describe a Docker container’s lifecycle.

Junior

Creation: A container is created from an image using docker create or docker run.
Running: It enters a running state with docker start or during creation with docker run.
Pausing: Containers can be paused and unpaused, freezing and unfreezing processes.
Stopping: The container is stopped using docker stop, which sends a stop signal followed by a kill signal if the container doesn't stop gracefully.
Restarting: A stopped container can be restarted with docker restart.
Deletion: The container is removed from the system with docker rm.

Q8.

Name the essential Docker commands and what they do.

Junior

docker run: Creates and starts a container from an image.
docker build: Builds an image from a Dockerfile.
docker pull: Pulls an image from a registry.
docker push: Pushes an image to a registry.
docker images: Lists all local images.
docker ps: Lists running containers (add -a to include stopped containers).
docker stop: Stops a running container.
docker start: Starts a stopped container.
docker rm: Removes one or more containers.
docker rmi: Removes one or more images.
docker exec: Executes a command in a running container.
docker logs: Fetches logs of a container.
docker compose: Manages multi-container applications.

Q9.

What is a Dockerfile, and how is it used in Docker?

Junior

A Dockerfile is a text file that contains instructions for building a Docker image. It specifies the base image, dependencies, environment settings, and commands to run.
Docker images are created from Dockerfiles using the docker build command.

Q10.

Explain the difference between a Docker image and a Docker container.

Junior

A Docker image is a lightweight, standalone, and executable package that includes everything needed to run a piece of software, including the code, runtime, libraries, environment variables, and config files. It's a read-only template.
A Docker container is a runnable instance of a Docker image. When an image is run, it exists in memory and has a writable layer over the image for storing application state. Containers are isolated environments, but share the OS kernel and, where appropriate, binaries and libraries.

Q11.

What is the purpose of Docker Compose?

Mid

Docker Compose is a tool for defining and running multi-container Docker applications. It uses a YAML file (docker-compose.yml) to configure the application's services, allowing you to orchestrate and manage multiple containers as a single service.
This simplifies the process of deploying complex applications that require multiple interconnected containers.

Q12.

What are Docker volumes?

Mid

Docker volumes are storage areas attached to containers, used for managing persistent data. They are important because:
- Data Persistence: Data in volumes survives container restarts and removals, ensuring data isn't lost.
- Data Sharing: Volumes can be shared and reused among multiple containers.
- Independent Lifecycle: Volumes have a lifecycle independent of the container, allowing data to persist beyond the life of a container.

Q13.

What is container orchestration?

Mid

Container orchestration is the automated management of containerized applications, including deployment, scaling, load balancing, and self-healing. It is essential in modern application deployment to ensure high availability, scalability, and efficient resource utilization in dynamic container environments.

Q14.

What is Kubernetes?

Mid

Kubernetes is an open-source platform for automating deployment, scaling, and operations of application containers across clusters of hosts.
It provides a framework to run distributed systems resiliently, handling scaling and failover for your application, providing deployment patterns, and more.

Q15.

Explain the concept of Docker image layers. How do they impact image size and build efficiency?

Mid

Docker images are composed of multiple layers, each representing a set of changes to the image. Layers are cached and shared among images, which makes builds more efficient.
When a change is made in a layer, only that layer and subsequent layers need to be rebuilt. This helps reduce image size and speeds up image builds.

Q16.

What is Docker Hub?

Mid

Docker Hub is a cloud-based registry service where users can discover, share, and store Docker images. It provides a centralized repository of public and private images.
Docker images can be pushed to Docker Hub for sharing with others and pulled from it to use in your environment.

Q17.

Explain the key concepts of Docker Swarm mode.

Mid

Docker Swarm is a native clustering and orchestration tool for Docker. Key concepts include:
- Nodes: Individual machines (physical or virtual) that join the swarm, categorized as "managers" (orchestrate and manage the swarm) or "workers" (run swarm services).
- Services and Tasks: A service defines the desired state of container instances in the swarm. Each instance, or task, is a single container.
- Load Balancing: Swarm automatically balances service tasks across nodes for optimal resource utilization.
- Scaling: Services can be scaled up or down to adjust the number of replicas of a given task.
- Rolling Updates: Swarm supports rolling updates to services, allowing for zero-downtime deployments.
- Networking: Swarm provides networking features to connect services within the swarm securely.

Q18.

What are Docker secrets and how can you use them?

Mid

Docker secrets are used to securely manage sensitive data like passwords or API keys in containers. They enhance security by preventing exposure of sensitive data.
You can use Docker secrets in a service by creating secrets and referencing them in the docker-compose.yml or Docker Swarm service configuration.
Example:

Q19.

What is Docker Desktop, and how does it differ from Docker Engine?

Mid

Docker Desktop is an application for MacOS and Windows that includes Docker Engine, a user-friendly interface, and additional features like Kubernetes integration and GUI-based management tools.
Docker Engine is the core part of Docker, the runtime that builds and runs containers.
The key difference is that Docker Desktop offers an integrated, easy-to-use environment with additional tools, while Docker Engine is the underlying technology that runs the containers.

Q20.

Explain the difference between Docker's CMD and ENTRYPOINT instructions in a Dockerfile.

Mid

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Q21.

What is Docker's "attach" mode, and how does it allow you to interact with running containers?

Mid

Q22.

Explain how Docker networking works.

Senior

Q23.

Can you describe the difference between bridge and overlay networks?

Senior

Q24.

Explain the purpose of Dockerfile multistage builds.

Senior

Q25.

What are the advantages of using Docker containers in a microservices architecture?

Senior

Q26.

What is a Docker Namespace?

Senior

Q27.

What is the difference between docker volumes and bind mounts?

Senior