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Docker Compose Cheat Sheet

Docker Compose is a tool for defining and running multi-container Docker applications. It uses a configuration file to provide all the necessary details about the services, networks, and volumes. Let's dive into the essential aspects of Docker Compose for programmers.

Building Images​

Building images is an essential step in the Docker Compose workflow. You can define the build context, Dockerfile path, and other parameters in the docker-compose.yml file for each service.

version: '3'
services:
  webapp:
    build:
      context: ./path_to_code
      dockerfile: Dockerfile.custom_name

This defines a service named webapp that uses the build context from ./path_to_code and a Dockerfile named Dockerfile.custom_name.

Running Images​

Once images are built, you can run them as containers using Docker Compose. The image to run can be specified in the docker-compose.yml file.

version: '3'
services:
  webapp:
    image: my_custom_image:latest

Here, the webapp service runs the image my_custom_image with the latest tag.

Basic Commands​

Docker Compose comes with a suite of commands to manage the lifecycle of your containers.

docker-compose up​

This command starts all the services defined in your docker-compose.yml file.

docker-compose up

When run, it reads the docker-compose.yml file and starts the services accordingly. You can also use -d flag to run services in detached mode.

docker-compose down​

Stops and removes all the services that are running.

docker-compose down

This command stops the services and also removes the containers, networks, and volumes defined in the docker-compose.yml file.

docker-compose logs​

Displays the logs of your services.

docker-compose logs webapp

In this case, it will show the logs for the service named webapp.

docker-compose build​

Builds the service images.

docker-compose build webapp

It builds the webapp service using the specified build context and Dockerfile in the docker-compose.yml file.

docker-compose ps​

List the services.

docker-compose ps

This command provides an overview of the current state of the services.

docker-compose.yml​

The docker-compose.yml file is a YAML file that defines the services, networks, and volumes for your application.

Defining Services​

Services are the heart of your application, representing the containers that will run.

services:
  webapp:
    image: my_custom_image:latest
    ports:
      - "5000:5000"

This defines a service webapp that runs the image my_custom_image:latest and maps port 5000 inside the container to port 5000 on the host.

Defining Networks​

Networks facilitate communication between containers.

services:
  webapp:
    image: my_custom_image
    networks:
      - my_custom_network

networks:
  my_custom_network:

This configuration sets up a custom network named my_custom_network and associates the webapp service with this network.

Common Keys​

There are multiple keys in the docker-compose.yml file that dictate the behavior of services, networks, and volumes.

For services, some common keys include:

  • image: The Docker image to use for the service.
  • build: Instructions to build the Docker image.
  • ports: Ports mapping between the host and the container.
  • volumes: Mount paths for data persistence.

Volumes​

Volumes are used for data persistence and sharing data among containers.

services:
  webapp:
    image: my_custom_image
    volumes:
      - my_data:/app/data

volumes:
  my_data:

Here, a volume named my_data is defined and mounted to /app/data in the webapp service container.

Secrets​

Secrets are used to manage sensitive data.

services:
  webapp:
    image: my_custom_image
    secrets:
      - my_secret

secrets:
  my_secret:
    file: ./path_to_secret_file

In this configuration, a secret named my_secret is defined, and its value is taken from the file at ./path_to_secret_file. The webapp service can then access this secret.

With this cheat sheet, you now have a comprehensive overview of the core components and functionalities of Docker Compose. Happy containerizing!