FROM instruction for base image in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the FROM instruction in a Dockerfile?

The FROM instruction sets the base image for the Docker image you want to build. It tells Docker which existing image to start from.

intermediate

Can a Dockerfile have multiple FROM instructions?

Yes, a Dockerfile can have multiple FROM instructions to create multi-stage builds. Each FROM starts a new stage.

beginner

How do you specify a specific version of a base image in the FROM instruction?

You add a tag after the image name, separated by a colon. For example, FROM ubuntu:22.04 uses Ubuntu version 22.04 as the base image.

beginner

What happens if you omit the tag in the FROM instruction?

If you omit the tag, Docker uses the 'latest' tag by default, which means it uses the most recent version of the image.

intermediate

Why is it important to choose a small base image in the FROM instruction?

Choosing a small base image reduces the final image size, making downloads and deployments faster and saving storage space.

What does the FROM instruction do in a Dockerfile?

A Runs a command inside the container

B Sets the base image for the build

C Copies files into the image

D Defines environment variables

The FROM instruction sets the base image that your Docker image builds upon.

How do you specify a version of an image in the FROM instruction?

A FROM image:version

B FROM image@version

C FROM version/image

D FROM image#version

You specify the version by adding a colon and the tag after the image name, like FROM ubuntu:20.04.

What tag does Docker use if none is specified in FROM?

A stable

B default

C latest

D base

Docker uses the 'latest' tag by default if no tag is specified.

Can a Dockerfile have more than one FROM instruction?

A No, only one FROM is allowed

B Yes, but only if images are the same

C No, it causes an error

D Yes, for multi-stage builds

Multiple FROM instructions are used to create multi-stage builds.

Why choose a smaller base image in FROM?

A It reduces image size and speeds up deployment

B It increases security automatically

C It is easier to write Dockerfiles

D It has more features

Smaller base images reduce the final image size, making downloads and deployments faster.

Explain the role of the FROM instruction in building a Docker image.

Think about how Docker knows what to build on top of.

Describe how to specify and why to choose a specific base image version in the FROM instruction.

Consider why you might not want to always use the latest version.