stacklink 0.1.0

Health checks, config validation, and structured logging for FastAPI

stacklink

Health checks, config validation, and structured logging for FastAPI — in three lines of code.

Built for solo devs and small teams who want production-grade infrastructure without the setup overhead.

Install

pip install stacklink

Quick start

from fastapi import FastAPI
from stacklink import Config, Field, health, logger

app = FastAPI()

class AppConfig(Config):
    env: str = Field(required=True)
    service: str = Field(default="my-api")
    port: int = Field(default=8080)
    db_url: str = Field(required=True, secret=True)

config = AppConfig()

logger.configure(config)
logger.info("server starting", port=config.port)

health.register(app, config=config)

That's it. You now have:

• Validated, typed config from .env and environment variables
• Structured JSON logging to stdout
• /healthz and /readyz endpoints on your FastAPI app

Modules

Config

Reads .env files and environment variables. Validates types. Fails loudly at startup if anything is wrong. Redacts secrets from output.

from stacklink import Config, Field

class AppConfig(Config):
    env: str = Field(required=True)
    port: int = Field(default=8080)
    db_url: str = Field(required=True, secret=True)

config = AppConfig()
config.as_dict()  # {"env": "production", "port": 8080, "db_url": "***"}

Supported types: str, int, float, bool. Bool coerces from true/false/1/0/yes/no.

Logger

Structured JSON logging. Every line is machine-parseable. Auto-tags with service name and environment when configured.

from stacklink import logger

logger.info("request handled", method="GET", path="/users", status=200)
# {"timestamp": "...", "level": "INFO", "message": "request handled", "method": "GET", "path": "/users", "status": 200}

Set LOG_LEVEL env var to control filtering (default: INFO).

Health

Registers /healthz (liveness) and /readyz (readiness) endpoints on your FastAPI app.

from stacklink import health

health.register(app, config=config)

async def check_database():
    try:
        await db.execute("SELECT 1")
        return True
    except Exception:
        return False

health.add_check("database", check_database)

/healthz always returns 200. /readyz returns 200 when all checks pass, 503 when any check fails.

Documentation

• Config
• Logger
• Health

Requirements

• Python 3.10+
• FastAPI 0.100+

Development

pip install -e ".[dev]"
pytest

License

MIT