Docker is foundational for backend, DevOps, and cloud roles, and its interviews test the core container model — images vs containers, how the Dockerfile and layers work, persistence with volumes, and networking. Here are the Docker interview questions that actually get asked, with answers. (See also our Kubernetes and DevOps guides.)
Images & containers
- What is the difference between an image and a container?
- Docker vs a virtual machine.
- What is a Dockerfile, and common instructions (FROM, RUN, COPY, CMD, ENTRYPOINT)?
- What are image layers and how does caching work?
- CMD vs ENTRYPOINT.
Storage & networking
- How do you persist data — volumes vs bind mounts?
- Docker networking — bridge, host, none.
- How do containers communicate?
- Port mapping (-p).
Compose & best practices
- What is Docker Compose and when do you use it?
- Multi-stage builds — why they matter.
- How do you reduce image size?
- Container lifecycle and orchestration (leads into Kubernetes).
How to prepare
Docker rounds probe the model and practical scenarios. Practise explaining images, layers, and volumes out loud. Greenroom runs spoken technical interviews that follow up on your reasoning. Pair it with our Kubernetes and DevOps guides.
Frequently asked questions
What are the most common Docker interview questions?
Common Docker questions cover image vs container, Docker vs virtual machines, the Dockerfile and its instructions, image layers and build caching, CMD vs ENTRYPOINT, data persistence (volumes vs bind mounts), networking (bridge, host, none), container communication, port mapping, Docker Compose, multi-stage builds, and reducing image size.
What is the difference between a Docker image and a container?
An image is a read-only template that packages an application and its dependencies, built from a Dockerfile in layers. A container is a running (or stopped) instance of an image with a writable layer on top. You can create many containers from one image, much like many objects from a class — the image is the blueprint, the container is the live instance.
What are Docker volumes and why are they used?
Volumes are Docker-managed storage that persists data outside a container's writable layer, so data survives when the container is removed or recreated. Unlike bind mounts (which map a host path directly), volumes are managed by Docker, more portable, and easier to back up. They're used for databases, uploaded files and any state that must outlive the container.
How should I prepare for a Docker interview?
Focus on the image/container model, how the Dockerfile and layer caching work, volumes vs bind mounts, networking, and multi-stage builds, since these are the core topics. Practise explaining why multi-stage builds shrink images and how layers cache, out loud with a voice-based mock interview that follows up, because Docker rounds probe the model and practical scenarios.