Build context concept in Docker - Mini Project: Build & Apply

Understanding Docker Build Context

📖 Scenario: You are preparing to create a Docker image for a simple web application. To do this, you need to understand how Docker uses the build context to include files during the image build process.

🎯 Goal: Learn how to set up a Docker build context by creating a Dockerfile and a simple application file, then build the Docker image using the correct context.

📋 What You'll Learn

Create a directory with a Dockerfile and an application file

Write a Dockerfile that copies the application file into the image

Use the docker build command with the correct build context

Verify the image contains the application file

💡 Why This Matters

🌍 Real World

Docker build context is essential when packaging applications into containers. It defines which files are sent to Docker daemon during image build.

💼 Career

Understanding build context helps DevOps engineers optimize Docker images and avoid common build errors related to missing files.

1

Create application file

Create a file named app.txt with the exact content Hello from Docker build context! in your current directory.

Docker

# Create a file named app.txt with the text 'Hello from Docker build context!'
# Your code here

Need a hint?

You can use the echo command to create the file with the text.

2

Create Dockerfile

Create a file named Dockerfile in the same directory with these exact lines:
FROM alpine
COPY app.txt /app.txt
CMD ["cat", "/app.txt"]

Docker

echo "Hello from Docker build context!" > app.txt
# Create a Dockerfile with FROM alpine, COPY app.txt /app.txt, and CMD ["cat", "/app.txt"]
# Your code here

Need a hint?

Use a text editor or shell redirection to create the Dockerfile with the exact lines.

3

Build Docker image with context

Run the command docker build -t myapp . in the directory containing Dockerfile and app.txt to build the Docker image named myapp using the current directory as the build context.

Docker

echo "Hello from Docker build context!" > app.txt
cat  Dockerfile
FROM alpine
COPY app.txt /app.txt
CMD ["cat", "/app.txt"]
EOF
# Build the Docker image named myapp using the current directory as context
# Your code here

Need a hint?

Use docker build with the -t option to name the image and . to specify the current directory as context.

4

Run Docker container to verify

Run the command docker run --rm myapp to start a container from the myapp image and display the content of /app.txt inside the container.

Docker

echo "Hello from Docker build context!" > app.txt
cat  Dockerfile
FROM alpine
COPY app.txt /app.txt
CMD ["cat", "/app.txt"]
EOF
docker build -t myapp .
# Run the container from myapp image to print the content of /app.txt
# Your code here

Need a hint?

Use docker run --rm myapp to run the container and see the output.