Multiple FROM statements in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does using multiple FROM statements in a Dockerfile allow you to do?

It allows you to create multi-stage builds, where you can use different base images in stages and copy only needed artifacts to the final image. This helps keep the final image small and clean.

beginner

How do you name a build stage when using multiple FROM statements?

You add an alias after the FROM statement like this: FROM node:18 AS builder. This name can be used later to copy files from that stage.

beginner

Why is multi-stage build useful in Docker?

It helps reduce the final image size by excluding build tools and intermediate files. You only keep what is necessary to run the application.

intermediate

What command copies files from one build stage to another in a multi-stage Dockerfile?

The COPY --from=stage_name /source/path /destination/path command copies files from a named build stage to the current stage.

intermediate

Can you use multiple FROM statements without naming stages?

Yes, but without names you cannot selectively copy files between stages. Naming stages is best practice for clarity and control.

What is the main benefit of using multiple FROM statements in a Dockerfile?

A To run multiple containers at once

B To allow multiple users to build the image

C To speed up Docker daemon startup

D To create multi-stage builds that reduce final image size

Multiple FROM statements enable multi-stage builds, which help reduce the final image size by copying only necessary files.

How do you refer to a previous build stage when copying files in a multi-stage Dockerfile?

A Using the stage alias with COPY --from=alias

B Using the image tag with COPY --image=tag

C Using the container ID with COPY --id=container

D Using the FROM statement again

You use the stage alias defined after FROM with COPY --from=alias to copy files from that stage.

Which of these is a correct syntax for naming a build stage?

A FROM python:3.12 LABEL builder

B FROM python:3.12 AS builder

C FROM python:3.12 STAGE builder

D FROM python:3.12 NAME builder

The correct syntax to name a build stage is 'FROM image AS name'.

What happens if you do not use multiple FROM statements in a Dockerfile?

A You cannot create multi-stage builds and the image may be larger

B Docker will automatically create multiple stages

C The build will fail

D You can still copy files from other images

Without multiple FROM statements, you cannot create multi-stage builds, so the image may include unnecessary build files.

Which command copies files from a previous build stage named 'builder'?

A COPY --image=builder /app/build /app

B COPY --stage=builder /app/build /app

C COPY --from=builder /app/build /app

D COPY --source=builder /app/build /app

The correct command to copy files from a named stage is COPY --from=builder.

Explain how multiple FROM statements help optimize Docker images.

Think about how you can separate building and running steps.

Describe the syntax and purpose of naming a build stage in a Dockerfile.

Naming helps copy files from one stage to another.