FROM instruction for base image in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Docker build with FROM alpine

What will be the base image used and the first line output when building this Dockerfile?

FROM alpine
RUN echo Hello World

Docker

FROM alpine
RUN echo Hello World

A

Base image: alpine
Output: Hello World

B

Base image: ubuntu
Output: Hello World

C

Base image: alpine
Output: RUN echo Hello World

D

Base image: scratch
Output: Hello World

💡 Hint

The FROM instruction sets the base image for the build.

The FROM alpine sets the base image to alpine. The RUN command executes and prints Hello World.

🧠 Conceptual

intermediate

Purpose of the FROM instruction

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

A To copy files into the image

B To specify the base image for the Docker build

C To run commands inside the container

D To expose ports from the container

💡 Hint

Think about what sets the starting point for building an image.

FROM sets the base image which is the starting point for the Docker image build.

❓ Configuration

advanced

Using multiple FROM instructions

What happens when a Dockerfile contains multiple FROM instructions?

A Only the first FROM is used; others are ignored

B The last FROM overrides all previous ones

C Docker throws a syntax error

D Each FROM starts a new build stage, allowing multi-stage builds

💡 Hint

Multiple FROM instructions enable building in stages.

Multiple FROM instructions create separate build stages, useful for multi-stage builds.

❓ Troubleshoot

advanced

Error when using invalid base image in FROM

What error will Docker show if the base image specified in FROM does not exist?

A manifest for <image> not found: manifest unknown: manifest unknown

B Syntax error near FROM instruction

C Permission denied while accessing base image

D Container exited with code 1

💡 Hint

Docker tries to pull the image and fails if it doesn't exist.

Docker reports manifest not found error when the base image is missing.

✅ Best Practice

expert

Choosing a base image for minimal size

Which base image is best to use in the FROM instruction for the smallest possible image size?

A debian

B ubuntu

C scratch

D centos

💡 Hint

One base image is completely empty and minimal.

scratch is an empty image with zero size, ideal for minimal images.