Targeting specific stages in Docker - Mini Project: Build & Apply

Docker Multi-Stage Build: Targeting Specific Stages

📖 Scenario: You are building a Docker image for a simple web application. To keep the image size small, you want to use multi-stage builds. You will create two stages: a builder stage that compiles the app, and a final stage that only contains the compiled app.

🎯 Goal: Build a Dockerfile with two stages named builder and final. Then, target the builder stage to build the image.

📋 What You'll Learn

Create a Dockerfile with a builder stage using the node:18 image

Create a final stage using the nginx:alpine image

Copy the compiled app from builder to final

Build the Docker image targeting the builder stage

💡 Why This Matters

🌍 Real World

Multi-stage builds are used in real projects to reduce image size and separate build dependencies from runtime environments.

💼 Career

Knowing how to target specific stages in Docker builds is important for DevOps roles to optimize container images and deployment pipelines.

1

Create the builder stage

Create a Dockerfile with a builder stage that uses the node:18 image and sets the working directory to /app.

Docker

# Your code here

Need a hint?

Use FROM node:18 AS builder to name the stage builder.

2

Add the final stage

Add a final stage that uses the nginx:alpine image and copies the /app/build directory from the builder stage to /usr/share/nginx/html.

Docker

FROM node:18 AS builder
WORKDIR /app
# Your code here

Need a hint?

Use COPY --from=builder to copy files from the builder stage.

3

Add a build command targeting the builder stage

Write the Docker build command that builds the image named myapp-builder targeting the builder stage.

Docker

FROM node:18 AS builder
WORKDIR /app

FROM nginx:alpine AS final
COPY --from=builder /app/build /usr/share/nginx/html
# Your code here

Need a hint?

Use docker build --target builder -t myapp-builder . to build only the builder stage.

4

Print the build command output

Run the build command docker build --target builder -t myapp-builder . and print the output showing the build stages.

Docker

FROM node:18 AS builder
WORKDIR /app

FROM nginx:alpine AS final
COPY --from=builder /app/build /usr/share/nginx/html

# Run the build command and show output
# Your code here

Need a hint?

Simulate the build output by printing a success message.