Named build stages in Docker - Mini Project: Build & Apply

Named Build Stages in Docker

📖 Scenario: You are creating a Docker image for a simple web application. To keep the image size small and organized, you will use named build stages.

🎯 Goal: Build a multi-stage Dockerfile using named build stages to separate the build environment from the final runtime environment.

📋 What You'll Learn

Create a Dockerfile with two named build stages: builder and final

In the builder stage, use the node:18 image and create a file /app/build.txt with the text Build complete

In the final stage, use the alpine:latest image and copy the /app/build.txt file from the builder stage

Print the contents of /app/build.txt when running the container

💡 Why This Matters

🌍 Real World

Using named build stages helps create smaller, cleaner Docker images by separating build tools from runtime environments.

💼 Career

Many DevOps and software engineering roles require writing efficient Dockerfiles with multi-stage builds to optimize deployment pipelines.

1

Create the builder stage

Create a Dockerfile with a named build stage called builder that uses the node:18 image. Inside this stage, create a directory /app and add a file /app/build.txt containing the text Build complete using a single RUN command.

Docker

# Start the Dockerfile with the builder stage
# Your code here

Need a hint?

Use FROM node:18 AS builder to name the build stage. Use RUN mkdir /app && echo "Build complete" > /app/build.txt to create the file.

2

Add the final stage

Add a second named build stage called final that uses the alpine:latest image. In this stage, copy the file /app/build.txt from the builder stage to the same path /app/build.txt.

Docker

FROM node:18 AS builder
RUN mkdir /app && echo "Build complete" > /app/build.txt

# Add the final stage using alpine:latest
# Your code here

Need a hint?

Use FROM alpine:latest AS final to start the final stage. Use COPY --from=builder /app/build.txt /app/build.txt to copy the file.

3

Add a command to display the file

In the final stage, add a command to run when the container starts that prints the contents of /app/build.txt using cat.

Docker

FROM node:18 AS builder
RUN mkdir /app && echo "Build complete" > /app/build.txt

FROM alpine:latest AS final
COPY --from=builder /app/build.txt /app/build.txt

# Add a command to print the file contents
# Your code here

Need a hint?

Use CMD ["cat", "/app/build.txt"] to print the file when the container runs.

4

Build and run the Docker image

Build the Docker image with the tag buildstage-demo and run a container from it. The output should be the text Build complete.

Docker

# Build the image
# Your code here

# Run the container
# Your code here

Need a hint?

Use docker build -t buildstage-demo . to build and docker run --rm buildstage-demo to run the container.