Docker: practice, test and prove it

Images and containers, Dockerfile instructions, layer caching, ports, volumes, Docker Compose and registries.

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Start the docker test Read the first lesson

Docker screenings check whether you can package an application and run it predictably. Questions usually show a short Dockerfile or a docker run command and ask what it does, why a build is slow, why data disappeared after a container was removed, or how one container reaches another.

This page tests those basics against the pass mark. The lessons cover writing a Dockerfile that builds quickly and runs correctly, and then running containers with ports, volumes and Compose, which together cover most first-job Docker tasks.

Benchmark: The pass mark is 80%, and Docker is commonly screened for DevOps, backend developer, cloud support and QA automation roles. Requirements vary by employer.

Lessons

Writing a Dockerfile: instructions and layer cachingWhat FROM, WORKDIR, COPY, RUN, CMD and ENTRYPOINT do, and how ordering steps well makes builds fast.Lesson 1

Running containers: ports, volumes and Docker ComposePublish ports, keep data with volumes, connect services in Compose, and push images to a registry.Lesson 2

Container lifecycle commands and debugging a container that will not stay upBuild, run, inspect, enter and clean up containers, and read exit codes and logs to explain why a container stopped.Lesson 3

Smaller, safer images: multi-stage builds, non-root users and health checksCut image size with multi-stage builds and .dockerignore, run as a non-root user, pin versions and add a HEALTHCHECK.Lesson 4

Interview prep

Docker interview questionsDocker questions common in DevOps and backend interviews, with answers that explain how things work.6 questions

Certificate

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Common questions

Do I need Linux to learn Docker?

Docker containers run on a Linux kernel, but Docker Desktop lets you practise on Windows and macOS. Basic Linux commands help because most images are Linux based.

Is Docker Compose the same as Kubernetes?

No. Compose runs several containers on one machine from a single file and is common for development and small setups. Kubernetes manages containers across many machines and is a larger topic.

Does this test cover writing Dockerfiles?

Yes. Several questions show Dockerfile instructions and ask what they do or how to improve them, so practise reading and writing short Dockerfiles.

Docker test for interviewWhat the screening round looks like, with a 5-question sample.