Layer caching and ordering in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Docker image layer?

A Docker image layer is a set of filesystem changes created by each command in a Dockerfile. Layers stack on top of each other to form the final image.

beginner

Why is layer caching important in Docker builds?

Layer caching speeds up Docker builds by reusing unchanged layers instead of rebuilding them, saving time and resources.

intermediate

How does the order of commands in a Dockerfile affect layer caching?

Commands at the top create layers that are cached first. If a command changes, all following layers must rebuild. So, order commands from least to most frequently changing to maximize cache use.

intermediate

What happens if you change a command in the middle of a Dockerfile?

Docker invalidates the cache for that layer and all layers after it, causing them to rebuild.

intermediate

Give an example of a good practice for ordering Dockerfile commands to optimize caching.

Place commands that change rarely, like installing system packages, near the top. Put commands that change often, like copying source code, near the bottom.

What does Docker use to speed up builds by reusing parts of previous builds?

A Layer caching

B Multi-stage builds

C Docker volumes

D Docker networks

Docker uses layer caching to reuse unchanged layers and speed up builds.

If you change a command in the middle of a Dockerfile, what happens to the cache?

A Only that layer rebuilds

B That layer and all following layers rebuild

C All layers rebuild

D Cache is not affected

Changing a command invalidates cache for that layer and all layers after it.

Which Dockerfile command should you place near the top to maximize caching?

A RUN apt-get install packages

B COPY source code

C CMD start app

D EXPOSE port

Commands that change rarely, like installing packages, should be near the top to maximize cache reuse.

What is a Docker image layer?

A A volume attached to a container

B A container running in the background

C A network configuration

D A set of filesystem changes from a Dockerfile command

Each Dockerfile command creates a layer representing filesystem changes.

Why should you order Dockerfile commands from least to most frequently changing?

A To reduce image size

B To make the Dockerfile easier to read

C To improve build speed by maximizing cache hits

D To avoid network errors

Ordering commands this way helps Docker reuse cached layers and speeds up builds.

Explain how Docker layer caching works and why the order of commands in a Dockerfile matters.

Think about how changing one step affects the rest.

Describe best practices for ordering commands in a Dockerfile to optimize build speed.

Consider what changes often and what stays the same.