Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.

This outline covers the features of Docker Compose and provides examples for using it to run the application.

Using Docker Compose

To use Docker Compose, you must install it. Docker Compose is included in Docker Desktop. If you are not using Docker Desktop, you can install Docker Compose separately by following the instructions found here.

For more information about Docker Compose, you can refer to the Docker Compose documentation.

Note:

This application uses Docker Compose version 3.9 or higher.

The example code in this outline will demonstrate the docker-compose commands.

Before running any commands, be sure to:

• Ensure that Docker Compose is installed.
• Make sure to set up Docker by running docker version in your command line.

To start the application with Docker Compose, run the following command in the application’s root directory:

docker-compose up -d
          

Running Tests

To run the tests using Docker Compose, run the following command in the application’s root directory:

docker-compose run web pytest 
          

Building the Application

To build the application using Docker Compose, run the following command in the application’s root directory:

docker-compose build 
          

This will build all the images defined in the docker-compose.yml file.

Defining Services

The docker-compose.yml file defines the services in the application. The file contains the following structure:

version: '3.9'
          
          services:
            web:
              build: .
              ports:
                - '8080:8080' 
              depends_on:
                - redis
            redis:
              image: redis:alpine
          

This file defines two services:

• web: The web service builds from the current directory and exposes port 8080, using a dependency on the redis service.
• redis: The redis service uses the image redis:alpine.

To modify the services in the application, you can edit the docker-compose.yml file and then rebuild and restart the application.

Scaling Services

To scale the application, you can use the docker-compose scale command.

Example: Scale the web service to 3 containers:

docker-compose scale web=3
          

Stopping Services

To stop the services, run the following command in the application’s root directory:

docker-compose down
          

This command will stop and remove all the containers, networks, and volumes created by Docker Compose.

Viewing Logs

To view logs from a service, run the following command:

docker-compose logs <service name>
          

For example, to view logs from the web service, run:

docker-compose logs web 
          

Executing Commands

To execute commands within a running container, use the docker-compose exec command.

Example: Run the command ls -l in the web container:

docker-compose exec web ls -l
          

Troubleshooting

If you encounter any issues running the application, you can use the following resources:

• Docker Compose Documentation
• Docker Forums
• Stack Overflow