When an application requires multiple services, such as databases and web servers, Docker Compose makes it easy to define and run multi-container applications. This chapter explores how to write docker-compose.yml configuration files and manage multiple containers with a single command.

Logo docker compose

What is Docker Compose?

Docker Compose is a tool that allows defining and managing multiple containers as a single application. With a docker-compose.yml file, we can specify services, networks, and volumes, and then run the entire environment with a single command.

This image shows how Docker Compose manages multiple containers

Structure of a docker-compose.yml File

The docker-compose.yml file defines each service in the application and how they should interact. Here is a basic structure of a docker-compose.yml file:

yaml

Basic Docker Compose Commands

Docker Compose allows managing the lifecycle of the multi-container application with simple commands.

Starting Services

To start all services defined in docker-compose.yml, use the command:

bash

Stopping Services

To stop all services, use the following command:

bash

Defining Services in Docker Compose

Each service in docker-compose.yml represents a container and can include configuration for ports, volumes, environment variables, and more.

Configuring Ports and Volumes

We can specify the ports and volumes needed for each service. This allows services to share data and be accessible externally.

Example of port and volume configuration:

yaml

Configuring Environment Variables

We can define environment variables that each service will use. This is useful for configuring application parameters without modifying the code.

yaml

Networks in Docker Compose

Docker Compose makes it easy to configure networks between services. By defining networks, services can communicate using their service names as hostnames.

Creating Custom Networks

Example of network configuration in docker-compose.yml:

yaml

Scaling Services with Docker Compose

Docker Compose allows scaling services to handle more traffic or improve availability. For example, we can scale the web service to run multiple containers.

bash

Conclusion

Docker Compose simplifies the management of multi-container applications, allowing you to define services, networks, and volumes in a single file. This facilitates the configuration and deployment of complex environments. In the next chapter, we will see best practices in Docker to optimize and manage containers efficiently.