Skills

docker-agents-generator

Installation
SKILL.md

docker-agents-generator

Generation Workflow

Execute these steps in order when containerizing an application:

1. Gather requirements (language, framework, database, cache)
2. Select Dockerfile template (language-specific)
3. Generate Dockerfile with multi-stage build
4. Generate .dockerignore for the language
5. Generate Compose configuration (dev and/or prod)
6. Generate .env template
7. Verify completeness

Step 1: Requirements Gathering

ALWAYS determine these before generating any files:

[ ] Language/runtime: Node.js | Python | Go | Java | Rust | .NET
[ ] Framework: Express, FastAPI, Gin, Spring Boot, Actix, ASP.NET, etc.
[ ] Target environment: development | production | both
[ ] Database: PostgreSQL | MySQL | MongoDB | Redis | none
[ ] Cache layer: Redis | Memcached | none
[ ] Message queue: RabbitMQ | Kafka | none
[ ] Reverse proxy: Nginx | Traefik | none
[ ] Needs file watch (dev): yes | no
[ ] Ports: application port(s)
[ ] Persistent data: volume requirements

Step 2: Dockerfile Template Decision Tree

Language?
├─ Node.js
│  ├─ Static frontend only? → multi-stage with nginx (see templates)
│  └─ Server app? → node:22-bookworm-slim runtime
├─ Python
│  ├─ ML/Data Science? → python:3.12-bookworm (full image)
│  └─ Web app? → python:3.12-slim-bookworm runtime
├─ Go
│  └─ ALWAYS → scratch or alpine runtime (static binary)
├─ Java
│  ├─ Spring Boot? → eclipse-temurin:21-jre-jammy runtime
│  └─ Other? → eclipse-temurin:21-jre-jammy runtime
├─ Rust
│  └─ ALWAYS → scratch or alpine runtime (static binary)
└─ .NET
   └─ ALWAYS → mcr.microsoft.com/dotnet/aspnet runtime

Base Image Selection Rules

  • ALWAYS use specific version tags, NEVER latest
  • ALWAYS use -slim or -bookworm-slim variants for runtime stages
  • ALWAYS use the full SDK image for build stages only
  • NEVER ship compilers, SDKs, or build tools in production images
  • ALWAYS include # syntax=docker/dockerfile:1 as the first line

Step 3: Generate Dockerfile

ALWAYS follow this structure for every generated Dockerfile:

# syntax=docker/dockerfile:1

# ---- Build Stage ----
FROM <sdk-image> AS build
WORKDIR /src
# 1. Copy dependency manifests first (cache optimization)
# 2. Install dependencies with cache mounts
# 3. Copy source code
# 4. Build application

# ---- Runtime Stage ----
FROM <minimal-image> AS runtime
# 1. Create non-root user
# 2. Copy built artifacts from build stage
# 3. Set ownership and permissions
# 4. Configure health check
# 5. Switch to non-root user
# 6. Expose port
# 7. Set ENTRYPOINT and CMD

Security Defaults (ALWAYS Apply)

# Non-root user — ALWAYS include
RUN groupadd -r appuser && useradd --no-log-init -r -g appuser appuser

# Health check — ALWAYS include
HEALTHCHECK --interval=30s --timeout=3s --start-period=10s --retries=3 \
  CMD <health-check-command> || exit 1

# Non-root execution — ALWAYS the last USER instruction
USER appuser

# Exec form — ALWAYS use for ENTRYPOINT
ENTRYPOINT ["/app/binary"]

Language-Specific Templates

See references/templates.md for complete, buildable templates for:

  • Node.js (server app + static frontend)
  • Python (pip + Poetry)
  • Go (static binary)
  • Java (Maven + Gradle)
  • Rust (cargo)
  • .NET (dotnet)

Step 4: Generate .dockerignore

ALWAYS generate a .dockerignore file. Select patterns based on language:

Universal Patterns (ALWAYS include)

.git
.gitignore
.dockerignore
Dockerfile
docker-compose*.yml
compose*.yaml
*.md
LICENSE
.env
.env.*
*.pem
*.key
.vscode
.idea
*.swp
.DS_Store
Thumbs.db

Language-Specific Additions

Language Additional Patterns
Node.js node_modules/, dist/, build/, .next/, coverage/, .npm/
Python __pycache__/, *.pyc, .venv/, venv/, .pytest_cache/, *.egg-info/
Go vendor/ (if not vendoring), *.test, *.out
Java target/, build/, .gradle/, *.class, *.jar (built in container)
Rust target/, *.rs.bk
.NET bin/, obj/, *.user, *.suo, packages/

Step 5: Generate Compose Configuration

Compose Template Decision Tree

What stack?
├─ Web + Database
│  └─ compose.yaml with app + db + named volume
├─ Web + Database + Cache
│  └─ compose.yaml with app + db + redis + named volumes
├─ Full Stack (frontend + backend + db + cache)
│  └─ compose.yaml with frontend + backend + db + redis + networks
├─ Development only
│  └─ compose.yaml with watch, bind mounts, debug ports
└─ Production only
   └─ compose.yaml with resource limits, restart policy, no bind mounts

Compose Generation Rules

  • NEVER include the version: field (deprecated)
  • ALWAYS use depends_on with condition: service_healthy
  • ALWAYS define health checks for database and cache services
  • ALWAYS use named volumes for persistent data
  • ALWAYS use env_file instead of hardcoded environment values
  • ALWAYS bind ports to 127.0.0.1 in development configurations
  • ALWAYS include resource limits in production configurations
  • ALWAYS use restart: unless-stopped in production
  • NEVER use container_name for services that may need scaling

See references/compose-templates.md for complete templates.

Step 6: Generate .env Template

ALWAYS generate a .env.example file alongside Compose configurations:

# Application
APP_PORT=3000
NODE_ENV=production

# Database
POSTGRES_USER=app
POSTGRES_PASSWORD=changeme
POSTGRES_DB=appdb

# Redis (if applicable)
REDIS_PASSWORD=changeme

# Secrets — NEVER commit actual values
# Copy this file to .env and fill in real values

Rules

  • ALWAYS include placeholder values, NEVER real secrets
  • ALWAYS add a comment warning not to commit .env
  • ALWAYS name the template .env.example (not .env)
  • ALWAYS reference it from Compose via env_file: .env

Step 7: Verification Checklist

After generating all files, verify:

[ ] Dockerfile: starts with # syntax=docker/dockerfile:1
[ ] Dockerfile: uses multi-stage build (build + runtime stages)
[ ] Dockerfile: dependency manifests copied before source code
[ ] Dockerfile: uses cache mounts for package managers
[ ] Dockerfile: non-root user created and activated
[ ] Dockerfile: HEALTHCHECK instruction present
[ ] Dockerfile: ENTRYPOINT uses exec form
[ ] Dockerfile: no secrets in ENV or ARG
[ ] Dockerfile: pinned base image versions (no :latest)
[ ] .dockerignore: exists and covers language-specific patterns
[ ] Compose: no version: field
[ ] Compose: depends_on uses condition: service_healthy
[ ] Compose: all databases have healthcheck defined
[ ] Compose: named volumes for persistent data
[ ] Compose: env_file used instead of hardcoded secrets
[ ] Compose: resource limits set (production configs)
[ ] .env.example: exists with placeholder values
[ ] .env.example: no real secrets committed

Common Generation Patterns

Development Compose with Watch

services:
  app:
    build:
      context: .
      target: build
    ports:
      - "127.0.0.1:3000:3000"
    env_file: .env
    develop:
      watch:
        - action: sync
          path: ./src
          target: /src/src
          ignore:
            - node_modules/
        - action: rebuild
          path: package.json

Production Compose Additions

services:
  app:
    build:
      context: .
      target: runtime
    restart: unless-stopped
    deploy:
      resources:
        limits:
          cpus: '1.0'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 128M

Database Health Checks (Copy-Paste Ready)

Database Health Check
PostgreSQL ["CMD-SHELL", "pg_isready -U $${POSTGRES_USER:-postgres}"]
MySQL ["CMD", "mysqladmin", "ping", "-h", "localhost"]
MongoDB ["CMD", "mongosh", "--eval", "db.adminCommand('ping')"]
Redis ["CMD", "redis-cli", "ping"]

Anti-Patterns to Avoid

See references/anti-patterns.md for the complete list. Critical ones:

  • NEVER generate a Dockerfile without multi-stage builds
  • NEVER generate Compose without health checks on databases
  • NEVER hardcode secrets in Dockerfiles or Compose files
  • NEVER omit .dockerignore when generating Docker infrastructure
  • NEVER use ADD when COPY suffices
  • NEVER run containers as root in generated configurations

Reference Links

Official Sources

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