fastapi-microservice/SKILL.md

---
name: fastapi-microservice
description: "Bootstrap FastAPI: SQLAlchemy, auth, Docker, one-pass build."
version: 1.0.0
author: Hermes Agent
license: MIT
platforms: [linux, macos]
metadata:
  hermes:
    tags: [fastapi, microservice, bootstrap, backend, python, docker]
    related_skills: [task-list-execution, writing-plans]
---

# FastAPI Microservice Bootstrap

## When to Use

The user asks to create a new FastAPI-based microservice. Signals:

- "создай каталог /opt/xxx, спланируем и напишем сервис"
- "нужен сервис для X с API на FastAPI"
- "bootstrap a new API service for Y"
- Any request where the output is a Python/FastAPI server with routes, database, and external integration

## Core Rules

### 1. No analysis preamble — start immediately

The user says "создай каталог и спланируем" — your first action is to create the directory. Do not:

- ❌ Summarize the requirement back to them
- ❌ Ask clarifying questions about scope
- ❌ Propose technology choices for approval
- ❌ Write a multi-step plan document before coding

✅ Instead: `mkdir -p /opt/project/app` → start writing files

**Investigation is part of execution, not preparation.** If you need to check Python version, installed packages, or port availability, do it as the first action of writing code, not as a preamble.

### 2. Build in layers, bottom-up

Write files in this order for maximum efficiency:

```
Layer 1 — Foundation
  ├── requirements.txt
  ├── .env.example
  ├── __init__.py files (empty, create dirs)
  ├── app/config.py           # pydantic-settings from env
  ├── app/security.py         # encryption, key generation
  ├── app/database.py         # async engine + session
  └── app/models.py           # ORM models (User, Account, etc.)

Layer 2 — Business logic
  ├── app/converters/         # domain-specific converters
  └── app/vk_client.py        # external API clients

Layer 3 — API
  ├── app/api/schemas.py      # Pydantic request/response
  ├── app/api/deps.py         # auth dependencies
  └── app/api/v1.py           # route handlers

Layer 4 — Entry point
  └── app/main.py             # FastAPI app + lifespan

Layer 5 — Infrastructure
  ├── Dockerfile
  ├── docker-compose.yml
  ├── Makefile
  └── .gitignore
```

### 3. Generate secrets and verify immediately

After writing code, do NOT stop at "code is written". Do:

1. Generate encryption key: `python3 -c "from cryptography.fernet import Fernet; print(Fernet.generate_key().decode())" > secrets/token_encryption_key`
2. Install deps: `pip install -r requirements.txt`
3. Verify all modules import: `python3 -c "from app import ..."`
4. Start server and test: curl health endpoint
5. Test at least one API endpoint (e.g. convert endpoint if it's a converter service)

### 4. Write all project files in one pass

Do not save README.md and STATUS.md separately from code. Write them last, after the code compiles and runs:

- **README.md** — API reference, usage examples, security, run instructions
- **STATUS.md** — implementation status table, phases, architecture diagram, how to run
- **Dockerfile** — multi-stage, slim, read-only rootfs, non-root user
- **docker-compose.yml** — service + volume + secret + healthcheck
- **Makefile** — dev/install/run/test/key/user commands

### 5. Security by default

Every microservice needs:

- **Encrypted secrets** — Fernet (AES-128-CBC + HMAC-SHA256), key from file/secret, NOT in code
- **API key auth** — sha256 hashed, not stored in plaintext
- **API key ≠ external token** — the API key lets you *use* the service, not read the upstream token
- **Minimal scope** — upstream tokens should have minimal permissions (e.g. VK wall scope only)
- **Docker read-only rootfs** — only /data writable
- **Non-root user** in Docker container

Log these in README.md as a security matrix table.

## Expected File Structure

```
/opt/<project-name>/
├── app/
│   ├── __init__.py
│   ├── main.py
│   ├── config.py
│   ├── database.py
│   ├── models.py
│   ├── security.py
│   ├── vk_client.py          # or external_api.py
│   ├── converters/
│   │   ├── __init__.py
│   │   └── markdown_to_vk.py # or relevant converter
│   └── api/
│       ├── __init__.py
│       ├── schemas.py
│       ├── deps.py
│       └── v1.py
├── tests/
│   └── (TODO after code)
├── secrets/
│   └── token_encryption_key  # NOT in git (.gitignore it)
├── Dockerfile
├── docker-compose.yml
├── requirements.txt
├── .env.example
├── .gitignore
├── Makefile
├── README.md
└── STATUS.md
```

## Common Pitfalls

| Pitfall | Fix |
|---------|-----|
| Writing README before code runs | Write docs last — they reflect what's real |
| Asking for approval on every file | Write all files in one batch, then verify |
| Skipping security docs | Include security matrix table in README |
| Not testing the API after writing code | Always start server and curl at least health + one endpoint |
| Using `&` in foreground terminal command | Use `terminal(background=True)` for server, then `curl` |
| Hand-typing code that could be written | Batch independent file writes in the same turn |
| Explaining the design before building | Say "Начинаю" and write files — the code IS the design |

## Verification Checklist

After writing all code:

- [ ] `pip install -r requirements.txt` succeeds
- [ ] All modules import: `python3 -c "from app import config, database, models, security, ..."`
- [ ] Encryption key generated and stored in secrets/
- [ ] Encrypt/decrypt round-trip works
- [ ] API keys generate and verify
- [ ] Converter (if any) produces correct output
- [ ] Server starts: `uvicorn app.main:app --host 0.0.0.0 --port N`
- [ ] `GET /api/v1/health` returns `{"status":"ok"}`
- [ ] At least one POST endpoint responds correctly (e.g. convert or account create)
- [ ] Swagger UI at `/docs` returns 200
- [ ] Dockerfile builds (if docker is available)

## Related Skills

- **task-list-execution** — for executing tasks from STATUS.md files
- **writing-plans** — for multi-step implementation plans with subagent delegation