Docker Skill

Container operations skill for building, deploying, and managing Docker containers across different platforms.

When to Use

Invoke this skill when:

• Building Docker images
• Managing docker-compose setups
• Deploying containers to Coolify or Hostinger
• Debugging container issues
• Viewing logs

Part 1: Building Images

Basic Build

# Build with default Dockerfile
docker build -t myapp:latest .

# Build with specific Dockerfile
docker build -f Dockerfile.prod -t myapp:prod .

# Build with build args
docker build --build-arg NODE_ENV=production -t myapp:prod .

# Multi-platform build
docker buildx build --platform linux/amd64,linux/arm64 -t myapp:latest .

Optimized Dockerfile Pattern

# Stage 1: Dependencies
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

# Stage 2: Build
FROM node:20-alpine AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
RUN npm run build

# Stage 3: Production
FROM node:20-alpine AS runner
WORKDIR /app
ENV NODE_ENV=production
COPY --from=builder /app/dist ./dist
COPY --from=deps /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/index.js"]

Part 2: Docker Compose

Development Setup

# docker-compose.yml
version: '3.8'

services:
  app:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
      - /app/node_modules
    environment:
      - DATABASE_URL=postgresql://user:pass@db:5432/mydb
    depends_on:
      - db

  db:
    image: postgres:15-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

Common Commands

# Start services
docker-compose up -d

# Stop services
docker-compose down

# View logs
docker-compose logs -f app

# Rebuild and restart
docker-compose up -d --build

# Run one-off command
docker-compose exec app npm run migrate

# Scale service
docker-compose up -d --scale worker=3

Part 3: Deployment to Coolify

Create Docker Compose App

# Create from docker-compose
mycli run coolify/apps/create-compose \
  --project_uuid "project-uuid" \
  --server_uuid "server-uuid" \
  --docker_compose_raw "$(cat docker-compose.prod.yml)"

Create from Dockerfile

# Create from GitHub repo with Dockerfile
mycli run coolify/apps/create-dockerfile \
  --project_uuid "project-uuid" \
  --server_uuid "server-uuid" \
  --repository "owner/repo" \
  --branch "main"

Deploy Updates

# Trigger deployment
mycli run coolify/deployments/deploy --uuid "app-uuid"

# Deploy specific tag
mycli run coolify/deployments/deploy-by-tag \
  --uuid "app-uuid" \
  --tag "v1.2.3"

Part 4: Deployment to Hostinger

Direct Docker Deployment

# List Docker projects
mycli run hostinger/vps/docker/list --vm_id "vm-id"

# Update project
mycli run hostinger/vps/docker/update \
  --vm_id "vm-id" \
  --project_id "project-id" \
  --compose_file "$(cat docker-compose.yml)"

# Restart after update
mycli run hostinger/vps/docker/restart \
  --vm_id "vm-id" \
  --project_id "project-id"

Part 5: Debugging

Container Logs

# View logs
docker logs mycontainer

# Follow logs
docker logs -f mycontainer

# Last N lines
docker logs --tail 100 mycontainer

# With timestamps
docker logs -t mycontainer

Remote Logs (Coolify)

# Get deployment logs
mycli run coolify/deployments/get --uuid "deployment-uuid"

Remote Logs (Hostinger)

# Get project logs
mycli run hostinger/vps/docker/logs \
  --vm_id "vm-id" \
  --project_id "project-id"

Interactive Shell

# Exec into running container
docker exec -it mycontainer /bin/sh

# As root
docker exec -u root -it mycontainer /bin/sh

Inspect Container

# Full inspection
docker inspect mycontainer

# Get IP address
docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' mycontainer

# Get mounted volumes
docker inspect -f '{{json .Mounts}}' mycontainer | jq

Resource Usage

# Live stats
docker stats

# Specific container
docker stats mycontainer

Part 6: Common Patterns

Health Checks

HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
  CMD curl -f http://localhost:3000/health || exit 1

Environment Files

# Use .env file
docker-compose --env-file .env.production up -d

# Pass individual vars
docker run -e API_KEY="secret" myapp

Volume Patterns

# Named volume (persistent)
volumes:
  - postgres_data:/var/lib/postgresql/data

# Bind mount (development)
volumes:
  - ./src:/app/src

# Anonymous volume (node_modules)
volumes:
  - /app/node_modules

Network Patterns

# Internal network
networks:
  internal:
    driver: bridge

services:
  app:
    networks:
      - internal
  db:
    networks:
      - internal

Troubleshooting

Container Won't Start

# Check logs
docker logs mycontainer

# Check exit code
docker inspect -f '{{.State.ExitCode}}' mycontainer

# Run interactively to see errors
docker run -it myapp /bin/sh

Port Already in Use

# Find what's using the port
lsof -i :3000

# Use different port
docker run -p 3001:3000 myapp

Out of Disk Space

# Clean up unused resources
docker system prune -a

# Clean volumes too
docker system prune -a --volumes

Network Issues

# List networks
docker network ls

# Inspect network
docker network inspect bridge

# Check container connectivity
docker exec mycontainer ping other-container