Introduction to Compose

Collin Dewey

02/20/2025

Compose

Docker/Podman Compose

What is Compose?

Managing multiple containers at a time. Managing multiple networks at a time.

Why use it over regular Docker or Kubernetes?

Kubernetes has lots of features that many people just don’t need. Running a bunch of different CLI commands for managing multiple containers is a pain.

What is in compose.yml

YAML Formatted File with definitions of…

Services
Networks
Volumes
Secrets

Services ¹

Name
OCI Image
Command
Volumes
Port Forwards
Container Dependencies
CPU/RAM Quotas
Capabilities
Environment Variables
Labels

Service Example

services:
  hugo:
    container_name: hugo
    image: klakegg/hugo
    command: --watch --destination /dest
    environment:
     - HUGO_ENV=production
    networks:
      - internal-network
    volumes:
      - ./src:/src
      - web-build-volume:/dest
    restart: unless-stopped

  nginx:
    container_name: nginx
    image: nginx:alpine
    mem_limit: 512m
    cpu_count: "4"
    labels:
      - are.containers.cool=true
    ports:
      - 8080:8080
    depends_on:
      - hugo
    networks:
      - web
      - internal-network
    volumes:
      - web-build-volume:/usr/share/nginx/html:ro
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./site.conf:/etc/nginx/conf.d/default.conf:ro
    restart: unless-stopped

Networks ²

Networks can be defined through Compose files

Name
Driver
Labels
Internal/External
- Internal networks are created by compose
- External networks are managed elsewhere (such as with Docker CLI)

networks:
  web-network:
    name: web-network
    external: true
  internal-network:
    name: internal-network
    driver: bridge

Volumes ³

Persistent folders that can be used across services

Name
Driver
Labels
External

volumes:
  web-build-volume:

Secrets ⁴

Secrets are data placed into the running container

Files
Environment Variables

secrets:
  cool_flag:
    file: ./flag.txt

Copies flag.txt to /run/secrets/cool_flag within the container.

Running Compose

docker compose	Purpose
up	Creates the containers, pulls or builds missing images
down	Tears down the containers, networks
logs	Prints STDOUT/STDERR from the container
pull	Downloads/Updates images, but doesn’t start containers
top	Lists internel container processes
exec (…)	Run command within container

Compose Flags

docker compose	Purpose
-f (PATH)	Use (PATH) as the compose.yml
up -d	Detach container, non-interactive
up –no-recreate	Uses existing containers
logs -f	Follows logs

What commands do I use most often?

docker compose pull
docker compose down
docker compose up --no-recreate -d

Container Management Tools

Name	Purpose
lazydocker	Look through containers, their logs, volumes, etc.
ctop	TUI for basic container managment.
dive	Looking through container layers.

Notes

Docker used to not come with compose. Instead using a package named docker-compose.

Use docker-compose instead of docker compose
Use docker-compose.yml instead of compose.yml

Podman Compose works as a drop-in replacment of Docker Compose