This document explains the structure and syntax of a docker-compose.yml file used to define and run multi-container Docker applications.
# Define the version of the Compose file format
version: '3.8'
# Define services, which are containers that make up your application
services:
# A service named 'web' for a web application
web:
# Specify the Docker image to use
image: nginx:alpine
# Define the ports forwarding - the format is <host>:<container>
ports:
- "80:80"
# Set environment variables
environment:
- NGINX_HOST=foobar.com
- NGINX_PORT=80
# Mount volumes - the format is <host>:<container>
volumes:
- ./html:/usr/share/nginx/html
# Define dependency on another service, ensuring it starts first
depends_on:
- app
# A service named 'app' for the main application
app:
# Build from a Dockerfile located in the specified directory
build: ./app
# Map the container port to the host
ports:
- "3000:3000"
# Mount volume for persistent storage
volumes:
- app_data:/var/lib/app_data
# Set the environment file
env_file:
- .env
# A service for a database
db:
image: postgres:latest
volumes:
- db_data:/var/lib/postgresql/data
environment:
- POSTGRES_USER=exampleuser
- POSTGRES_PASSWORD=examplepass
- POSTGRES_DB=exampledb
# Define networks for communication between containers
networks:
app_net:
driver: bridge
# Define volumes for persistent data storage
volumes:
app_data:
driver: local
db_data:
driver: local
# This docker-compose file runs three services: `web`, `app`, and `db`, each configured for a specific role within the application.
# Notes:
# - `version` specifies which version of the Docker Compose file format we're using
# - `services` is where you define your app's services
# - `web`, `app`, and `db` are examples of individual services that make up the app
# - `image` specifies which Docker image to use for the service
# - `build` specifies the location of the Dockerfile for building the image
# - `ports` allows you to map ports from the host to the container
# - `environment` is for setting environment variables within the container
# - `volumes` is for persistent data and mounting paths between the host and container
# - `networks` defines the networking for your services