Docker
20 min
Day 35: Docker Compose for multi-service dev
Compose: describing your whole stack declaratively
Instead of typing out docker run commands with networks and volumes by hand, docker-compose.yml describes every service, its image/build context, ports, volumes, and dependencies — then docker compose up builds/starts everything together, on one auto-created network.
A real multi-service example (this course's own stack)
services:
api:
build: ./api
ports:
- '3000:3000'
environment:
- DB_HOST=db
- REDIS_HOST=redis
depends_on:
- db
- redis
db:
image: postgres:16
volumes:
- pgdata:/var/lib/postgresql/data
environment:
- POSTGRES_PASSWORD=devpassword
redis:
image: redis:7
volumes:
pgdata:"depends_on" only waits for the container to start, not to be ready
Postgres's container can be running before Postgres itself is actually accepting connections. Real apps add a retry loop or a healthcheck (healthcheck: in Compose) rather than assuming depends_on guarantees readiness.
Key terms
- docker-compose.yml
- A declarative file describing a multi-container application's services, networking, and volumes.
Your API container crashes on startup because Postgres "isn't ready yet" even though depends_on lists it. What's the real fix?
