Docker Compose

Docker Compose has two parts:

• YAML file which describes the configuration of the containers
• CLI tool which is used for local testing/ automation using the YAML file

Compose is not meant for production usage its meant for quick local environment development
An new network interface is always created for containers created from a config file

Compose File Structure

The docker-compose file has 3 main parts:

• Services
• Volumes (Optional)
• Networks (Optional)

The first line in the file always needs to be the version of compose to use
It is recommended to use version 2 at the very least
If this line is not specified it defaults to version 1

Inside services we can specify multiple “servicename”
Each service name refers to a container
The service name need not be the same as the container name but it will be the name used as hostname on the network

Inside a compose file we can build custom containers as well
It will be build when docker compose up is run and the image does not exist in cache docker compose build can also be used to build images

Whenever compose creates any asset (image, volume, network, etc.) it will prepend the current working directory name to the name that we specify

docker compose up 			# Start containers and log on terminal
docker compose up -d 		# Start containers in detached state
 
docker compose down 		# Stop containers/ Cleanup
docker compose down -v 		# Stop containers and remove volumes as well
 
docker compose ps 			# View running containers
docker compose top 			# View services running in container
docker compose logs 		# View logs

If we have files called docker-compose.yaml and docker-compose.override.yaml in the folder when we run docker compose up the override file will overwrite conflicting options from the base compose file

If we want to specify override files with using the default names it can be specified in the docker compose up command using the -f flag
The first file specified needs to be the base file

# Using multiple config files
docker compose -f docker-compose.yml -f docker-compose.test.yml up -d
 
# Squish multiple config files into one file
docker compose -f docker-compose.yml -f docker-compose.prod.yml config

Options
-f: Alternate Compose File
-p: Alternate Project Name (Default : Directory name)

Compose file version 3 reference | Docker Docs

Overview of docker-compose CLI | Docker Documentation