Docker In Docker

Docker-in-Docker

Overview

Docker-in-Docker (DinD) lets you build images, run containers, and use Docker Compose from inside a dev container. This is essential for projects that build container images as part of their workflow or run integration tests against containers.

Enable the Feature

{
  "features": {
    "ghcr.io/devcontainers/features/docker-in-docker:2": {
      "version": "latest",
      "dockerDashComposeVersion": "v2"
    }
  }
}

Feature Options

Docker-in-Docker vs Docker-outside-of-Docker

Use DinD when:

• You need full isolation (CI, untrusted builds)
• Building images that should not affect the host
• Running in Codespaces (no host socket available)

Use DooD when:

• You want to share the host's image cache
• Running locally and want faster builds

Full Example

{
  "name": "Container Build Environment",
  "image": "mcr.microsoft.com/devcontainers/base:ubuntu",
  "features": {
    "ghcr.io/devcontainers/features/docker-in-docker:2": {
      "version": "latest",
      "dockerDashComposeVersion": "v2",
      "installDockerBuildx": true
    }
  },
  "postCreateCommand": "docker compose version",
  "customizations": {
    "vscode": {
      "extensions": ["ms-azuretools.vscode-docker"]
    }
  }
}

Running Containers Inside the Dev Container

Once DinD is enabled, docker and docker compose work normally:

# Build an image
docker build -t my-app .

# Run a service stack
docker compose up -d

# Run integration tests against a container
docker run --rm -d -p 5432:5432 postgres:16

Compose for Dev Dependencies

Create a docker-compose.test.yml for containers needed during development:

services:
  postgres:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: devpass
    ports:
      - "5432:5432"
  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

Then start them in postStartCommand:

{
  "postStartCommand": "docker compose -f docker-compose.test.yml up -d"
}

Best Practices

• Prefer DinD in Codespaces — there is no host Docker socket to mount.
• Use postStartCommand (not postCreateCommand) to launch containers so they restart on every Codespace resume.
• Add "installDockerBuildx": true if you use multi-stage or multi-platform builds.
• Set resource limits on inner containers to avoid exhausting the Codespace machine.
• Use named volumes in Compose files so data persists across container restarts.