Squashing layers in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why squash Docker image layers?

What is the main benefit of squashing layers in a Docker image?

A It automatically updates the base image to the latest version.

B It increases build speed by caching all layers separately.

C It reduces the final image size by combining multiple layers into one.

D It splits the image into multiple smaller images for easier distribution.

💡 Hint

Think about how layers add up in size and how combining them affects the image.

Squashing merges multiple layers into a single one, which reduces the overall image size and can improve deployment efficiency.

💻 Command Output

intermediate

Output of Docker build with --squash

What output will you see when running docker build --squash -t myapp . if the Docker daemon supports squashing?

A Successfully built <image_id> with all layers squashed into one.

B Error: unknown flag: --squash

C Warning: --squash ignored, using default layering.

D Build completed but layers remain separate.

💡 Hint

Consider if the Docker daemon supports the experimental feature for squashing.

If the daemon supports squashing, the build output confirms success and shows the image ID with layers combined.

❓ Configuration

advanced

Enable Docker experimental features for squashing

Which configuration change enables Docker's experimental features to allow layer squashing?

A Run Docker with --enable-experimental flag every time.

B Set environment variable DOCKER_SQUASH=enabled before building.

C Install a separate Docker plugin for squashing layers.

D Add "experimental": true to the daemon.json file and restart Docker.

💡 Hint

Think about Docker daemon configuration files and how to enable experimental features globally.

Adding "experimental": true in /etc/docker/daemon.json enables experimental features like --squash, requiring a Docker restart.

❓ Troubleshoot

advanced

Why does --squash flag cause an error?

You run docker build --squash -t myapp . but get the error: "unknown flag: --squash". What is the most likely cause?

A Docker daemon experimental features are not enabled.

B The Dockerfile syntax is incorrect.

C The build context directory is missing.

D The Docker client version is too new for this flag.

💡 Hint

Check if the Docker daemon supports the feature you are trying to use.

The --squash flag requires experimental features enabled on the Docker daemon; otherwise, it is unknown and causes an error.

🔀 Workflow

expert

Best workflow to minimize image size with squashing

Which workflow best minimizes Docker image size using squashing while keeping build cache benefits?

A Squash all layers in every build to one layer immediately.

B Use multi-stage builds and squash only the final stage layers.

C Build without squashing, then manually delete intermediate images.

D Use a single RUN command for all steps without squashing.

💡 Hint

Consider how multi-stage builds and squashing can work together to optimize size and caching.

Multi-stage builds allow separating build and runtime stages; squashing only the final stage reduces size without losing cache benefits from earlier stages.