201 — Building Images with Dockerfile

Learn to create custom Docker images using Dockerfiles. Understand image layers, caching, and best practices for efficient image builds.

Learning Objectives

Write your first Dockerfile

Understand Dockerfile instructions and syntax

Build custom images from Dockerfiles

Leverage layer caching for faster builds

Tag and manage custom images

Step 1

Create your first Dockerfile

Set up a simple project directory and create a basic Dockerfile.

Commands to Run

mkdir my-first-image && cd my-first-image

cat > Dockerfile << 'EOF'
FROM ubuntu:22.04
RUN apt-get update && apt-get install -y curl
CMD ["echo", "Hello from my custom image!"]
EOF

cat Dockerfile

What This Does

A Dockerfile is a text file with instructions to build an image. FROM specifies the base image, RUN executes commands during build, and CMD sets the default command when containers start.

Expected Outcome

You'll have a Dockerfile with three instructions. The cat command displays its contents to verify it was created correctly.

Pro Tips

1
Dockerfile must be named exactly 'Dockerfile' (capital D)
2
Each instruction creates a new layer in the image
3
Instructions are executed top to bottom during build
4
Use a text editor like vim, nano, or VSCode for complex Dockerfiles