Multiple Compose files (override) in Docker - Mini Project: Build & Apply

Using Multiple Docker Compose Files to Override Settings

📖 Scenario: You are working on a web application that uses Docker Compose to run a web server and a database. You want to create a base Compose file for the common setup and an override Compose file to change the web server's port for development.

🎯 Goal: Learn how to create and use multiple Docker Compose files to override service settings without changing the base configuration.

📋 What You'll Learn

Create a base Docker Compose file named docker-compose.yml with a web and db service

Create an override Docker Compose file named docker-compose.override.yml to change the web service port

Use the docker compose command to start the services with the override applied

Verify the web service is running on the new port

💡 Why This Matters

🌍 Real World

In real projects, multiple Compose files let developers keep a stable base setup and customize it for different environments like development, testing, or production without duplicating all settings.

💼 Career

Understanding how to use multiple Docker Compose files is important for DevOps roles to manage containerized applications efficiently and maintain clean, reusable configurations.

1

Create the base Docker Compose file

Create a file named docker-compose.yml with two services: web using the image nginx:alpine and db using the image postgres:alpine. Set the web service to expose port 80.

Docker

# Create docker-compose.yml with web and db services
# Your code here

Need a hint?

Use the services key to define both web and db services with their images and ports.

2

Create the override Docker Compose file

Create a file named docker-compose.override.yml that overrides the web service port to 8080 instead of 80.

Docker

version: '3.8'
services:
  web:
    # Override the port to 8080
    # Your code here

Need a hint?

Only include the web service and override the ports key to map port 8080 on the host to port 80 in the container.

3

Start the services using both Compose files

Run the docker compose command to start the services using both docker-compose.yml and docker-compose.override.yml files together.

Docker

# Run the docker compose command with both files
# Your code here

Need a hint?

Use docker compose up -d to start the services in detached mode. Docker Compose automatically uses both files if named docker-compose.yml and docker-compose.override.yml.

4

Verify the web service is running on port 8080

Run the command docker compose ps and check that the web service is mapped to port 8080 on the host.

Docker

# Run the command to check running services
# Your code here

Need a hint?

Use docker compose ps to list running containers and their port mappings. Look for 0.0.0.0:8080->80/tcp under the web service.