Docker Project Foundations Agent Skill

Docker Project Foundations

Overview

This skill guides you in Dockerizing a project from scratch. It focuses on creating the initial Docker file set, choosing a sane layout, and preferring containerized dependencies over host-level installs.

When to use this skill

Activate this skill when:

• A user asks you to set up, initialize, or Dockerize a project
• A project needs an initial Dockerfile, compose.yaml, or .dockerignore and does not have one
• A user wants to add a service dependency (database, cache, message queue) to a project
• A user asks how to run or develop a project locally and Docker is available

Do not use this skill when

Do not use this skill when:

• The user explicitly wants to avoid Docker
• The project already has a mature Docker setup and only needs minor edits
• The main task is optimizing an existing Dockerfile
• The main task is editing or debugging an existing Compose stack

Core guidance

Always create these three files

When Dockerizing a project, always produce all three:

• .dockerignore — Create this first so the initial build context is small and safe. See assets/dockerignore-example for a reference.
• Dockerfile — Create a working starter image definition that the project can build and run with. See assets/Dockerfile.simple.
• compose.yaml — Create a local development stack that includes the application service and any required dependencies. See assets/compose-dev.yaml.

npm registry credentials

• Exclude .npmrc at every depth with **/.npmrc in .dockerignore; otherwise a broad source copy can persist credentials in image layers.
• The Node.js starter mounts npmrc as a BuildKit secret for both npm ci steps. Public-package builds need no secret. For private registries, pass the config explicitly:

  DOCKER_BUILDKIT=1 docker build --secret id=npmrc,src="$HOME/.npmrc" .

Use the actual config path if the project keeps it elsewhere. Never copy the credential file or pass its values through ARG or ENV. Dependency scripts run during installation can access the mounted secret; use trusted dependencies and a least-privilege registry token.

• For private-registry builds through Compose, add this optional override as compose.npm.yaml alongside the starter's compose.yaml:

  services:
    app:
      build:
        secrets:
          - npmrc
  secrets:
    npmrc:
      file: ${NPMRC_PATH:?Set NPMRC_PATH to your npm config file}

Build with NPMRC_PATH="$HOME/.npmrc" docker compose -f compose.yaml -f compose.npm.yaml build. This grants build-time access only, not a runtime secret. Public-package builds should omit the override so no credential file is required.

Prefer Dockerized dependencies over host installs

When a project needs a database (Postgres, MySQL, MongoDB), cache (Redis, Memcached), queue (RabbitMQ, Kafka), or any other infrastructure service:

• Always define it as a service in compose.yaml instead of telling the user to install it on the host.
• Never suggest brew install postgres, apt install redis, or similar host-level installs for development dependencies.
• Use official Docker images from Docker Hub for these services.
• Configure services with environment variables, not config files baked into images.

Bootstrap checklist

• Name the file compose.yaml rather than legacy Compose filenames.
• Put all three files at the project root unless there is a clear multi-service layout that justifies a docker/ subdirectory.
• Ensure the initial setup can build and start locally with one command path.
• Bind published application ports to loopback by default. Widen the host address only when another device must reach the development service.
• Keep unauthenticated datastores on the Compose network instead of publishing their ports. If local host tools require database access, publish only to loopback.
• If a development-only credential fallback enables one-command startup, label it clearly and document a .env override.
• Use Compose services for local databases, caches, and queues instead of host installs.
• Keep the first scaffold simple; defer detailed image optimization and advanced Compose tuning to the owning skills.

Development vs production

• Development: Use bind mounts for live reload, publish application ports on loopback by default, and enable verbose logging. Keep unauthenticated datastores on the Compose network; publish a datastore port only on loopback when local host tools require it.
• Production: Use multi-stage builds, copy only built artifacts, do not mount source code, minimize image layers, set appropriate resource limits.
• Keep a single Dockerfile that supports both via build stages and build arguments when possible.

File placement

• Place Dockerfile at the project root (or in a docker/ subdirectory if the project has multiple services).
• Place compose.yaml at the project root.
• Place .dockerignore at the project root, next to the Dockerfile.

Related skills

• For Dockerfile optimization, cache strategy, non-root execution, and image hardening, use docker-build-strategies.
• For service dependencies, health checks, overrides, volumes, networks, and Compose debugging, use docker-compose-patterns.
• For destructive Docker CLI commands (docker system prune, docker rm -f, image/network/builder pruning) and a cross-product index of destructive-command guardrails, use docker-destructive-guardrails.

References

• references/project-structure.md — Detailed guidance on Docker project file organization, naming conventions, and multi-service layouts.

Assets

• assets/dockerignore-example — A comprehensive .dockerignore for a typical project.
• assets/compose-dev.yaml — A development-oriented Compose file with Dockerized dependencies.
• assets/Dockerfile.simple — A basic multi-stage Dockerfile following best practices.

Scripts

• scripts/verify-setup.sh — Checks required files exist and validates compose.yaml.

  bash scripts/verify-setup.sh [--help]

Exit status is 0 when verification succeeds or help is requested, 1 when required files are missing or the Compose configuration is invalid, and 2 for invalid arguments.

Checks

• checks/verification.md — Detailed verification checklist for manual review.