How do I prepare for a Docker interview?

Work through realistic questions, read why each answer is right, then redo the ones you missed. This test has ten, taken from what interviewers commonly ask a beginner or a junior. Then read the postings: the 1,513 open jobs that name Docker show what employers expect on top of it.

Is this Docker test free?

Yes. It needs no account and no email, runs in your browser and sends nothing anywhere.

What does my score mean?

It is a self-check. Eight or more right means the basics are fresh; five to seven means a good base with gaps; under five means more practice first. It is not an official certificate.

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Home / Skill tests / Docker

Docker test: 10 questions to check yourself

In plain words: Docker packs a program together with everything it needs, so it runs the same way on a laptop and on a server. Answer ten questions, press the button, and see which you got right and why.

1,513 open jobs name Docker today, with a median advertised pay of $198K. The questions are the kind that come up in a first interview.

1What is a container?A running instance of an image, isolated from the rest of the machineA kind of virtual disk you must pay forA text file with settingsA full copy of another computer

2What is an image?A screenshot of the appA read-only template from which containers are startedA running containerA password

3Which file describes how to build an image?Dockerfiledocker.jsonREADMEimage.txt

4What does docker ps show?The images on the machineThe running containersThe network settingsThe Docker version

5What happens to files written inside a container when the container is deleted?They are kept foreverThey are lost, unless they were stored in a volumeThey move to the imageThey go to the cloud

6What does docker run -p 8080:80 nginx do?Starts nginx and makes its port 80 reachable on port 8080 of your machineStarts nginx on port 80 only inside the container, with no access from outsideStarts 8080 copies of nginxDownloads nginx without starting it

7What is Docker Compose for?Writing musicDescribing and starting several containers that work together, such as an app and its database, from one fileMaking images smallerBacking up containers

8Why does the order of lines in a Dockerfile matter for build speed?It does not matterEach line is cached; a changed line makes all the lines after it run againDocker reads the file from the bottomOnly the last line is run

9Where do images usually come from?A registry such as Docker Hub, or one your company runsOnly from your own machineFrom the operating systemFrom email

10Which is the safer choice for a program inside a container?Run it as the root userRun it as an ordinary user with only the rights it needsRun it with every right, so nothing failsIt does not matter

Questions about this test

How do I prepare for a Docker interview?: Work through realistic questions, read why each answer is right, then redo the ones you missed. This test has ten, taken from what interviewers commonly ask a beginner or a junior. Then read the postings: the 1,513 open jobs that name Docker show what employers expect on top of it.
Is this Docker test free?: Yes. It needs no account and no email, runs in your browser and sends nothing anywhere.
What does my score mean?: It is a self-check. Eight or more right means the basics are fresh; five to seven means a good base with gaps; under five means more practice first. It is not an official certificate.

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