Scratch base image for minimal containers in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the scratch base image in Docker?

The scratch base image is an empty image with no files or operating system. It is used to build minimal containers containing only your application and its dependencies.

beginner

Why use the scratch image for containers?

Using scratch creates very small containers, improving security and performance by including only what is necessary to run the app.

beginner

How do you specify the scratch image in a Dockerfile?

You write FROM scratch at the top of your Dockerfile to start building from an empty base image.

intermediate

What must you include in a container built from scratch to make it runnable?

You must add your application binary and any required files manually because scratch has no OS or tools.

beginner

Give an example of a simple Dockerfile using scratch.

Example:

FROM scratch
COPY myapp /
CMD ["/myapp"]

This copies a binary myapp into the container and runs it.

What does the scratch image contain?

A A minimal Linux OS

B A full Ubuntu system

C Nothing, it is empty

D Only shell utilities

The scratch image is completely empty with no files or OS.

Which Dockerfile line starts a build from the scratch image?

A FROM scratch

B FROM ubuntu

C FROM alpine

D FROM base

You specify FROM scratch to start from an empty image.

Why might you choose scratch over other base images?

A To create the smallest possible container

B To get a full OS environment

C To have pre-installed tools

D To use a graphical interface

Scratch is used to build minimal containers with only your app.

What must you do when using scratch as base image?

A Nothing, it has everything needed

B Install an OS inside the container

C Use a package manager

D Manually add your app and dependencies

Since scratch is empty, you must add your app and any needed files.

Which command runs your app in a scratch-based container?

A RUN /myapp

B CMD ["/myapp"]

C ENTRYPOINT /bin/bash

D START /myapp

You use CMD with the path to your app binary to run it.

Explain what the scratch base image is and why it is useful.

Think about what is inside the image and what you need to add.

Describe how to create a Dockerfile using the scratch image to run a simple binary.

Focus on the minimal steps needed in the Dockerfile.