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Docker and Kubernetes

How containers are built and run with Docker, and how Kubernetes schedules, connects and heals them. Written for engineers who deploy and debug containerised apps.

Engineering

AShared by Alex Chen

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Writing Dockerfiles and Building Images

The Dockerfile instructions, how the build cache works, and how to build images that are small, fast to rebuild and do not run as root.

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Content

41 total questions

MCQ: 10

Fill-in: 8

Flashcards: 12

Pair match: 11

Writing Dockerfiles and Building Images – Flashcards

Flashcards

Card #1

FROM

Card #2

RUN

Card #3

COPY

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Writing Dockerfiles and Building Images – MCQ

Multiple Choice Questions

1. In a Node.js Dockerfile, COPY . . comes before RUN npm ci, and every code change reinstalls all the dependencies. What fixes it?
- Add RUN npm cache clean --force on the line after the install step
- Copy package.json and the lockfile, run npm ci, then copy the rest
- Switch the base image to a slim variant of the same Node.js version
- Move the WORKDIR instruction so it comes after the npm ci step runs
2. A Dockerfile has RUN apt-get update on one line and RUN apt-get install -y curl on the next. Months later, a package you add to the install line fails to download. Why?
- The cached update layer still holds an old package index
- apt-get install only works when it is in the first RUN line
- Each RUN line starts from an empty filesystem, so no index exists
- The base image deletes the apt index between each pair of RUN lines
3. One RUN step downloads a 300 MB archive and the next RUN step deletes it. How much does this add to the image?
- Nothing, because the later layer removes it from the image
- About 150 MB, because deleted files are compressed in later layers
- Nothing once docker image prune has run on the build machine
- Still about 300 MB, because the earlier layer keeps the file

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Writing Dockerfiles and Building Images – Fill-in-the-blank

Fill in the Blank

1. To keep a secret out of every layer, BuildKit can mount it for a single step with RUN --mount=type=___.
Answer:secret
Hint: The mount type is named after what it carries
2. RUN --mount=type=___ keeps a package manager's download folder between builds without storing it in the image.
Answer:cache
Hint: Where downloads are kept for reuse
3. The flag COPY --___=app:app sets the owner of the copied files in the same step, so no separate layer is needed to change ownership.
Answer:chown
Hint: The Linux command that changes a file's owner

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Writing Dockerfiles and Building Images – Pair match

Pair Match

WORKDIR↔Sets the working directory for the instructions that follow

LABEL↔Adds key-value metadata to the image

HEALTHCHECK↔Command Docker runs to test whether the container is healthy

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