Building images in Compose in Docker - Mini Project: Build & Apply

Building images in Compose

📖 Scenario: You are working on a small web project that uses Docker Compose to manage services. You want to build a custom Docker image for your web service using a Dockerfile.

🎯 Goal: Learn how to define a Docker Compose file that builds a Docker image from a Dockerfile and runs a container from that image.

📋 What You'll Learn

Create a Dockerfile with a simple base image

Create a docker-compose.yml file that builds the image from the Dockerfile

Define a service in Compose that uses the built image

Run the Compose setup and verify the container runs

💡 Why This Matters

🌍 Real World

Building images in Compose is common when you want to customize your app environment and easily run multiple services together.

💼 Career

DevOps engineers and developers use Docker Compose to manage multi-container applications and automate image builds.

1

Create a Dockerfile

Create a file named Dockerfile with these exact contents:
FROM alpine:latest
CMD ["echo", "Hello from custom image"]

Docker

# Create a Dockerfile with FROM alpine:latest and CMD ["echo", "Hello from custom image"]

Need a hint?

The Dockerfile must start with FROM alpine:latest and end with CMD ["echo", "Hello from custom image"].

2

Create docker-compose.yml with build config

Create a file named docker-compose.yml with a service called web that builds the image from the current directory using the build key.

Docker

FROM alpine:latest
CMD ["echo", "Hello from custom image"]

# Create docker-compose.yml with service 'web' that builds from current directory
# Your code here

Need a hint?

The Compose file must have services: with a web: service that uses build: . to build from the current folder.

3

Add ports mapping to the service

In the docker-compose.yml file, add a ports section under the web service that maps port 8080 on the host to port 80 in the container.

Docker

FROM alpine:latest
CMD ["echo", "Hello from custom image"]

version: '3.8'
services:
  web:
    build: .
    # Add ports mapping 8080:80 below
    # Your code here

Need a hint?

Indent the ports: section under web: and add - "8080:80" to map ports.

4

Run docker-compose and show container output

Run docker-compose up --build --abort-on-container-exit in the terminal to build the image and start the container. Then, write a command to display the container logs using docker-compose logs web.

Docker

FROM alpine:latest
CMD ["echo", "Hello from custom image"]

version: '3.8'
services:
  web:
    build: .
    ports:
      - "8080:80"

# Run docker-compose up with build and abort on exit
# Then show logs of web service
# Your code here

Need a hint?

Use docker-compose up --build --abort-on-container-exit to build and run, then docker-compose logs web to see the output.