Compose

Docker/Podman Compose

By Collin Dewey

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
docs.docker.com/reference/compose-file/services

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)
docs.docker.com/reference/compose-file/networks
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:
docs.docker.com/reference/compose-file/volumes

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.

docs.docker.com/reference/compose-file/secrets

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