Compose watch for development in Docker - Mini Project: Build & Apply

Compose watch for development

📖 Scenario: You are building a simple development environment using Docker Compose. You want to automatically restart your application container whenever you change the source code files. This helps you see your changes immediately without manually restarting the container.

🎯 Goal: Create a Docker Compose setup that watches for file changes in your app directory and restarts the container automatically during development.

📋 What You'll Learn

Create a Docker Compose file with a service named app

Mount the local ./app directory into the container

Use the restart: always policy initially

Add a command to run a simple watch script inside the container

Print a message showing the container restarts on file changes

💡 Why This Matters

🌍 Real World

Developers often want their code changes to reflect immediately without restarting containers manually. This setup helps automate that during development.

💼 Career

Knowing how to configure Docker Compose for live development is a valuable skill for DevOps engineers and developers working with containerized applications.

1

Create the initial Docker Compose file

Create a file named docker-compose.yml with a service called app that uses the image alpine. Mount the local directory ./app to /app inside the container.

Docker

# Create docker-compose.yml with service app using image alpine
# Mount ./app to /app

Need a hint?

Use volumes to mount the local folder ./app into the container path /app.

2

Add restart policy and working directory

In the app service, add restart: always and set working_dir to /app.

Docker

version: '3.8'
services:
  app:
    image: alpine
    volumes:
      - ./app:/app
    # Add restart policy and working directory here

Need a hint?

The restart key controls container restart behavior. working_dir sets the default directory inside the container.

3

Add a command to watch for file changes

Add a command to the app service that runs sh -c "while true; do inotifywait -e modify,create,delete -r /app && echo 'Files changed, restarting...'; sleep 1; done". This will watch for file changes in /app and print a message.

Docker

version: '3.8'
services:
  app:
    image: alpine
    volumes:
      - ./app:/app
    restart: always
    working_dir: /app
    # Add command to watch files here

Need a hint?

Use inotifywait inside a shell loop to watch for file changes and print a message.

4

Print a message when container starts

Add a command that first prints "Starting watch on /app" then runs the watch loop. Use sh -c with echo followed by the while true loop.

Docker

version: '3.8'
services:
  app:
    image: alpine
    volumes:
      - ./app:/app
    restart: always
    working_dir: /app
    # Update command to print start message and then watch files

Need a hint?

Chain commands in sh -c using semicolon ; to print a message before the loop.