Docker Compose

What it is

Docker Compose is a tool for defining and running applications consisting of multiple Docker containers. A compose.yaml file describes all services, networks, and volumes, and a single command brings them all up.

Basic compose.yaml

services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      DATABASE_URL: postgres://db:5432/app
  
  db:
    image: postgres:16
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: app
 
volumes:
  pgdata:

Essential commands

docker compose up: bring up all services
docker compose up -d: bring up in background
docker compose down: stop and remove containers
docker compose logs -f: follow logs from all services
docker compose exec web sh: shell into a service

Use cases

Local microservices development
Testing environments with real dependencies
Quick demos and prototypes
CI/CD for integration tests

Compose vs Kubernetes

Aspect	Docker Compose	Kubernetes
Purpose	Local development, CI	Production, orchestration at scale
Complexity	Low — one YAML file	High — multiple resources (Deployments, Services, Ingress)
Scaling	Manual (`scale: 3`)	Automatic (HPA, VPA)
Networking	Default bridge network	CNI plugins, service discovery
State	Stateful with local volumes	StatefulSets, PersistentVolumes
Migration	—	Kompose converts compose files to K8s manifests

Why it matters

Docker Compose allows defining multi-container applications as code. For local development, it replaces complex setup scripts with a single command that starts databases, caches, and auxiliary services in the correct order.

References

Docker Compose Documentation — Official documentation.
Compose File Reference — Docker, 2024. Complete file format reference.
Docker Overview — Docker, 2024. General Docker and Compose context.