Multi Container Workspaces

Multi-Container Workspaces

Overview

Multi-container workspaces use Docker Compose to run sidecar services (databases, caches, queues) alongside the main dev container. The dev container connects to sidecars over the Compose network, giving you a production-like topology in development.

Basic Setup

docker-compose.yml

services:
  app:
    build:
      context: .
      dockerfile: .devcontainer/Dockerfile
    volumes:
      - ..:/workspace:cached
    command: sleep infinity

  db:
    image: postgres:16
    restart: unless-stopped
    environment:
      POSTGRES_USER: dev
      POSTGRES_PASSWORD: devpass
      POSTGRES_DB: myapp
    volumes:
      - pgdata:/var/lib/postgresql/data

  redis:
    image: redis:7-alpine
    restart: unless-stopped

volumes:
  pgdata:

devcontainer.json

{
  "name": "Full Stack App",
  "dockerComposeFile": "docker-compose.yml",
  "service": "app",
  "workspaceFolder": "/workspace",
  "runServices": ["app", "db", "redis"],
  "shutdownAction": "stopCompose",
  "forwardPorts": [3000, "db:5432", "redis:6379"],
  "postCreateCommand": "npm ci && npm run db:migrate",
  "remoteEnv": {
    "DATABASE_URL": "postgresql://dev:devpass@db:5432/myapp",
    "REDIS_URL": "redis://redis:6379"
  }
}

Key Properties

Multiple Compose Files

Override the base Compose file with a dev-specific overlay:

{
  "dockerComposeFile": [
    "docker-compose.yml",
    "docker-compose.dev.yml"
  ],
  "service": "app"
}

The dev overlay can add volumes, environment variables, or features only needed in development.

Compose Override Example

# docker-compose.dev.yml
services:
  app:
    volumes:
      - ..:/workspace:cached
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
    command: sleep infinity

Service Networking

All services in the same Compose file share a network. Reference sidecars by their service name:

• db:5432 — PostgreSQL
• redis:6379 — Redis
• rabbitmq:5672 — RabbitMQ
• azurite:10000 — Azure Storage emulator

No localhost — always use the service name as the hostname.

Health Checks and Dependencies

Ensure sidecars are ready before running setup commands:

services:
  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U dev"]
      interval: 5s
      timeout: 3s
      retries: 5

  app:
    depends_on:
      db:
        condition: service_healthy

Parallel postCreateCommand

Run multiple setup steps concurrently:

{
  "postCreateCommand": {
    "backend": "dotnet restore",
    "frontend": "npm ci",
    "migrations": "npm run db:migrate",
    "seed": "npm run db:seed"
  }
}

Best Practices

• Always use "shutdownAction": "stopCompose" to clean up sidecar containers when the Codespace stops.
• Use named volumes for database data so it survives container rebuilds.
• Add health checks to sidecar services and depends_on with condition: service_healthy for the app service.
• Reference sidecars by service name, never localhost — they are separate containers on the Compose network.
• Keep sidecar images pinned to major versions (e.g., postgres:16, not postgres:latest) for reproducibility.
• Use remoteEnv for connection strings so they are available in the integrated terminal.
• Separate dev-only configuration into a docker-compose.dev.yml overlay to keep production Compose files clean.