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The FROM instruction

Learn to specify a base image with FROM.

The FROM instruction

FROM chooses the base image the image is built on. The choice directly affects the image size and security:

  • python:3.12: Debian based, full (~1 GB)
  • python:3.12-slim: unnecessary packages removed (~150 MB)
  • python:3.12-alpine: based on Alpine Linux (~50 MB); can cause trouble with some packages because of musl libc
FROM python:3.12-slim

Pinning the version

Writing FROM node can bring a different Node version on every build. Pin the version; to be even more exact you can use the image digest:

FROM node:20-alpine
FROM node:20.18.0-alpine3.20
FROM node@sha256:3f2a…     # immutable: exactly the same image

FROM scratch is a completely empty image; it is used for statically compiled Go programs.

Practice Choosing a base image

Write the first two lines of a Dockerfile for a Node.js application: base image node:20-alpine, working directory /app.

Starter code

terminal
# buraya yaz

Sample solution

terminal
FROM node:20-alpine
WORKDIR /app

Expected output

[+] Building 4.2s (8/8) FINISHED
 => naming to docker.io/library/api:latest done

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What benefit usually comes with a small image?

  • A faster CPU
  • More memory
  • Automatic backups
  • Faster downloads and less security attack surface Correct answer

Explanation: A package not in the image has no vulnerabilities either.

2 Choose a lightweight Python base.

Question 
FROM python:3.12-____
Answer 
FROM python:3.12-slim

Explanation: The -slim tag is the Debian variant with unnecessary packages removed.

3 Match the base images.

Term Meaning
python:3.12 Full Debian, ~1 GB
python:3.12-slim Trimmed, ~150 MB
python:3.12-alpine Alpine, ~50 MB
scratch Empty image

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project