002-Compose-Demo

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Docker Compose Demo - Multi-Container Application

Description

This lab demonstrates a practical Docker Compose example with a multi-container application. You'll explore a complete docker-compose-sample.yml file that defines three interconnected services: a web server, an application, and a database.

Prerequisites

• Docker and Docker Compose installed
• Basic understanding of Docker concepts
• Completion of the previous lab (001-intro)

Lab Overview

This docker-compose-sample.yml file defines a multi-container application with three services: web, app, and db. Below is a detailed explanation of each section:

Services

1. web Service

• Image: Uses the official nginx:latest image.
• Container Name: The container is named web-container.
• Ports: Maps port 8080 on the host to port 80 in the container.
• Environment Variables:
  • NGINX_HOST: Set to localhost.
  • NGINX_PORT: Set to 80.
• Volumes: Mounts the ./web-data directory on the host to /usr/share/nginx/html in the container, allowing you to serve custom static files.
• Networks: Connects to the webnet network.
• Restart Policy: Always restarts the container if it stops.

2. app Service

• Build: Builds the image from a Dockerfile located in the ./app directory.
• Container Name: The container is named app-container.
• Ports: Maps port 3000 on the host to port 3000 in the container.
• Environment Variables:
  • NODE_ENV: Set to production.
• Dependencies: Depends on the db service, ensuring the database starts before the app.
• Networks: Connects to both webnet and dbnet networks.
• Restart Policy: Restarts the container on failure.

3. db Service

• Image: Uses the official postgres:latest image.
• Container Name: The container is named db-container.
• Environment Variables:
  • POSTGRES_USER: Set to user.
  • POSTGRES_PASSWORD: Set to password.
  • POSTGRES_DB: Set to mydb.
• Volumes: Mounts a named volume db-data to /var/lib/postgresql/data in the container, persisting database data.
• Networks: Connects to the dbnet network.
• Restart Policy: Restarts the container unless stopped manually.

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Volumes

• db-data: A named volume used by the db service to persist PostgreSQL data.

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Networks

• webnet: A custom network used by the web and app services to communicate.
• dbnet: A custom network used by the app and db services to communicate.

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This Compose file demonstrates how to define services, manage dependencies, and configure networks and volumes for a multi-container application.

Lab Exercises

1. Examine the Sample File: Review the docker-compose-sample.yml file to understand the service definitions
2. Analyze Service Dependencies: Study how the app service depends on the db service
3. Understand Networking: See how services communicate through custom networks
4. Review Volume Management: Learn how data persistence is handled with named volumes

Key Learning Points

• Multi-service Architecture: How to structure applications with multiple containers
• Service Dependencies: Using depends_on to control startup order
• Network Isolation: Creating separate networks for different tiers
• Data Persistence: Using volumes to maintain database state
• Port Mapping: Exposing services to the host system

Next Steps

After completing this lab, you'll understand:

• How to structure a real-world multi-container application
• The relationship between web servers, applications, and databases
• Best practices for service configuration in Docker Compose

Navigation

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