Docker Compose for Local Dev

Docker Compose for Local Dev

Step 1 of 10

 

 

 

One file describes the whole app: two services, a volume, and who waits for whom.

The Idea

A compose.yaml declares an app's services, networks and volumes in one file, and docker compose up starts them together. Compose puts every service on a default network where each is reachable by its service name. depends_on orders startup, but by default waits only for a container to run, not to be ready.

Real-World Example

An API and Postgres come up with one command. The API reaches the database at db:5432 — the container port, not the host port — and waits for it with condition: service_healthy and a pg_isready healthcheck.

The Tradeoff

Compose drives a single Docker Engine: ideal for development and CI, but spreading replicas across machines and rescheduling them when one dies is what an orchestrator like Kubernetes adds. docker compose down removes containers and the network but keeps named volumes unless you pass -v.

Hands-On

# illustrative — compose.yaml for local development
services:
  api:
    build: .
    ports: ["8080:8000"]
    environment: { DATABASE_URL: "postgres://postgres:dev@db:5432/postgres" }
    depends_on:
      db: { condition: service_healthy }
  db:
    image: postgres:17
    environment: { POSTGRES_PASSWORD: dev }
    healthcheck: { test: ["CMD-SHELL", "pg_isready -U postgres"], interval: 5s }
    volumes: ["pgdata:/var/lib/postgresql/data"]
volumes:
  pgdata: {}

Your turn

Put the steps in the right order.

1. 1The healthcheck passes: db is healthy↑↓
2. 2docker compose up creates the project's default network↑↓
3. 3api starts and connects to db:5432↑↓
4. 4db starts and its healthcheck begins↑↓

Check order

Mini quiz

1 / 3

Inside a Compose project, the API should reach the database at:

• Alocalhost:5432
• Bdb:5432
• CThe host port mapped to 5432
• DThe container's IP, looked up by hand

Sources

• How Compose works — Docker Docs
• Networking in Compose — Docker Docs
• Control startup and shutdown order — Docker Docs
• docker compose down — Docker Docs