51 Must-Know Docker Interview Questions for Top Tech Companies

This article compiles 51 commonly asked Docker interview questions covering fundamentals, commands, configuration, networking, resource management, security, and comparisons with related technologies.

What is Docker?

What is a Docker image?

What is a Docker container?

How many states can a Docker container have?

What is the most common specification in a Dockerfile?

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

What are the common Docker commands?

Which commands copy data between a container and the host?

Command to start an nginx container with random port mapping and mount a local directory to the container's html?

Explain the ONBUILD instruction in a Dockerfile.

What is Docker Swarm?

How to monitor Docker in production?

How does Docker run containers on non‑Linux systems?

How to batch clean temporary image files?

How to view environment variables supported by an image?

Where are local image files stored?

What principles should be followed when building Docker images?

If a container exits and is not shown by docker ps, is data lost?

How to stop all running containers?

How to batch clean stopped containers in the background?

How to temporarily exit an interactive container terminal without terminating it?

How to view output and logs of background‑running application containers?

When using docker port to map a container port, the system reports "NO public port '80' published for …" – what does this mean?

Can multiple application processes run in a single container?

How to control a container's share of system resources (CPU, memory)?

What is the relationship between a repository, a registry, and an index? (including errors when pulling from non‑official registries)

Where is Docker's configuration file located and how to modify it?

How to change Docker's default storage settings?

What are the differences between Docker and LXC (Linux Containers)?

What are the differences between Docker and Vagrant?

In a development environment, how to choose between Docker and Vagrant?

How to migrate a Docker environment from one host to another?

After creating a Docker container, if the network namespace file under /var/run/netns is deleted, can it be manually restored?

What is a Docker image? (duplicate for emphasis)

Explain the basic Docker usage workflow.

What is docker‑compose?

What is Docker's union file system?

Which type of applications (stateless or stateful) are more suitable for Docker containers?

What are the differences between Docker and virtual machines?

Is Docker secure?

How to clean stopped background containers?

How to view environment variables supported by an image? (duplicate)

When starting a container, an "exec format error" occurs – how to resolve it?

Where are local image files stored? (duplicate)

How to exit a container's bash without terminating it? (duplicate)

How to automatically remove a container on exit?

How to quickly view local images and containers?

What is Docker Hub?

How far can Docker containers scale?

When a Docker container exits, is data lost? (duplicate)

The questions are gathered from publicly available online sources for free sharing and are intended to help candidates prepare for Docker‑related interview topics.