Write a Dockerfile

Write a production-ready Dockerfile for my application.

Application details:
- Language/runtime: [NODE.JS / PYTHON / GO / etc.]
- Framework: [EXPRESS / FASTAPI / GIN / etc.]
- Entry point: [HOW THE APP STARTS]
- Port: [WHAT PORT IT LISTENS ON]
- Environment variables needed: [LIST THEM]
- Build step required: [YES/NO — describe if yes]

Requirements:
- Multi-stage build to keep image small
- Non-root user for security
- Correct WORKDIR setup
- Efficient layer caching (.dockerignore compatible)
- Health check if applicable
- Include a .dockerignore file contents at the end

Add a brief comment on each major section explaining what it does.