Docker layer caching in CI - Mini Project: Build & Apply

Docker Layer Caching in CI

📖 Scenario: You are working on a project where you build Docker images frequently in a Continuous Integration (CI) pipeline. To save time and resources, you want to use Docker layer caching so that unchanged layers are reused instead of rebuilt every time.This project will guide you through setting up a simple Dockerfile and configuring a CI build script to use Docker layer caching effectively.

🎯 Goal: Build a Docker image with caching enabled in a CI environment to speed up repeated builds by reusing unchanged layers.

📋 What You'll Learn

Create a Dockerfile with multiple layers

Add a cache key variable in the CI build script

Use Docker build command with cache-from option

Print the Docker build output to verify caching

💡 Why This Matters

🌍 Real World

Docker layer caching helps speed up builds in CI pipelines by reusing unchanged layers, saving time and computing resources.

💼 Career

Understanding Docker caching is essential for DevOps engineers to optimize CI/CD pipelines and reduce build times in real projects.

1

Create a Dockerfile with multiple layers

Create a file named Dockerfile with these exact lines:
FROM python:3.12-slim
RUN apt-get update && apt-get install -y curl
COPY app.py /app/app.py
CMD ["python", "/app/app.py"]

Docker

# Create the Dockerfile with the specified content
# Your code here

Need a hint?

Each line in the Dockerfile creates a layer. Make sure to write the lines exactly as shown.

2

Add a cache key variable in the CI build script

In a file named build.sh, create a variable called CACHE_KEY and set it to myapp-cache.

Docker

# Create CACHE_KEY variable
# Your code here

Need a hint?

Just write CACHE_KEY=myapp-cache exactly in the script.

3

Use Docker build command with cache-from option

In the build.sh file, add a Docker build command that uses --cache-from with the image named $CACHE_KEY and tags the new image as myapp:latest.

Docker

# Add docker build command with --cache-from
# Your code here

Need a hint?

Use the exact command docker build --cache-from=$CACHE_KEY -t myapp:latest .

4

Print the Docker build output to verify caching

Add a command in build.sh to print the output of the Docker build command so you can see if layers are cached.

Docker

# Print the output of the docker build command
# Your code here

Need a hint?

Capture the output of the docker build command in a variable and then print it using echo.