Named build stages in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a named build stage in Docker?

A named build stage is a part of a Dockerfile where you give a name to a build step. This helps you reuse or copy files from that stage later in the build process.

beginner

How do you name a build stage in a Dockerfile?

You name a build stage by adding AS <name> after the FROM instruction, like FROM node:18 AS builder.

intermediate

Why use named build stages in Docker?

Named build stages let you create multi-step builds. You can build your app in one stage and copy only the needed files to the final image, making it smaller and cleaner.

beginner

How do you copy files from a named build stage?

Use COPY --from=<stage-name> <source> <destination> to copy files from a named stage to the current stage.

beginner

Example: What does this line do? <br>FROM python:3.12 AS builder

It starts a build stage named 'builder' using the Python 3.12 image. You can refer to this stage later to copy files or build on it.

How do you name a build stage in a Dockerfile?

A RUN stage-name FROM image

B FROM image AS stage-name

C COPY stage-name FROM image

D STAGE image AS stage-name

You name a build stage by writing FROM image AS stage-name.

What is the main benefit of using named build stages?

A To reuse build steps and reduce final image size

B To avoid using Docker Compose

C To run containers faster

D To make the Dockerfile longer

Named build stages help reuse steps and keep the final image small.

Which command copies files from a named build stage?

A COPY --from=stage-name source destination

B RUN --from=stage-name source destination

C FROM --copy=stage-name source destination

D ADD --from=stage-name source destination

COPY --from=stage-name copies files from a named build stage.

Can you have multiple named build stages in one Dockerfile?

A No, only one stage is allowed

B Only two stages are allowed

C Yes, you can have many named stages

D Stages cannot be named

Dockerfiles can have many named build stages for multi-step builds.

What happens if you don’t name a build stage?

A You cannot build the image

B The build will be faster

C Docker will name it automatically as 'default'

D The stage is unnamed and can’t be referenced later

Unnamed stages can’t be referenced later with COPY --from.

Explain what named build stages are and why they are useful in Docker.

Think about how you can split building and packaging in steps.

Describe how to copy files from one build stage to another using named build stages.

Focus on the COPY command with --from option.