Get started with Docker-Compose

Docker-compose is your tool of choice when you want to run more than one Docker container at a time, like in a full-stack application with a backend, frontend, and DB. In this blog post, we’ll explore how to use Docker Compose to run a web application consisting of a frontend application built with React, a backend API built with Python Flask, and a PostgreSQL database.

The Docker Compose File

The first step is to create a Docker Compose file that defines the services for the application. Create a file called docker-compose.yml in the root directory of your project and add the following services:

version: '3.9'
services:
  frontend:
    build: ./frontend
    ports:
      - "3000:3000"
  backend:
    build: ./backend
    ports:
      - "5000:5000"
    environment:
      - FLASK_ENV=development
      - POSTGRES_HOST=db
    depends_on:
      - db
  db:
    heroImage: postgres:latest
    environment:
      - POSTGRES_USER=myuser
      - POSTGRES_PASSWORD=mypassword
      - POSTGRES_DB=mydatabase

In this configuration, we define three services: frontend, backend, and db. The frontend and backend services are built using Dockerfiles in the ./frontend and ./backend directories, respectively. The db service uses the latest version of the PostgreSQL image.

Run the Application

To run docker-compose application, navigate to the root directory of your project and run the following command:

docker-compose up --build

This command will start all three services and build any necessary Docker images. The --build flag ensures that Docker Compose builds new images if necessary.

You can also build the application using

docker-compose build

Using the Application Once the application is running, you can access the frontend application by visiting http://localhost:3000 in your web browser. The backend API is available at http://localhost:5000/api.

Connecting to the Database The PostgreSQL database can be accessed using a PostgreSQL client or any PostgreSQL-compatible ORM. To connect to the database, use the following connection string:

postgresql://myuser:mypassword@localhost/mydatabase

This string assumes you have defined the environment variables for the PostgreSQL username, password, and database name in your Docker Compose file.

That was a quick walkthrough to set up your app with docker-compose