reqly 0.1.0

Auto-instrumentation SDK for FastAPI and Flask: zero-code latency, error rates, and status codes shipped to a Reqly collector.

Reqly

Auto-instrumentation SDK for FastAPI and Flask. One line captures latency, status codes, and error rates for every request and ships them to an Reqly collector.

Install

pip install reqly

(For local development against this monorepo: pip install -e ./sdk[dev].)

Usage

from fastapi import FastAPI
import reqly

app = FastAPI()
reqly.instrument(app, service_name="checkout-api")

from flask import Flask
import reqly

app = Flask(__name__)
reqly.instrument(app, service_name="checkout-api")

instrument() auto-detects FastAPI vs Flask — no other code changes needed.

Configuration

Every option can be passed as a kwarg to instrument() or set via environment variable. Resolution order: kwarg > env var > default.

kwarg	env var	default
service_name	REQLY_SERVICE_NAME	sys.argv[0] basename
collector_url	REQLY_COLLECTOR_URL	http://localhost:8000
api_key	REQLY_API_KEY	None
sample_rate	REQLY_SAMPLE_RATE	1.0
flush_interval_seconds	REQLY_FLUSH_INTERVAL_SECONDS	5.0
max_batch_size	REQLY_MAX_BATCH_SIZE	200
max_queue_size	REQLY_MAX_QUEUE_SIZE	2000
ignore_routes	REQLY_IGNORE_ROUTES (comma-separated)	/health,/metrics
capture_request_body	REQLY_CAPTURE_REQUEST_BODY	False

Design guarantees

• Fails open. Any internal SDK error is caught and logged once; instrumentation then disables itself rather than risk repeatedly raising into your app. A slow or unreachable collector never slows down your app — all shipping happens off a background thread with strict per-phase HTTP timeouts.
• Bounded cardinality. Captured routes are the framework's matched route template (/users/{id}), never the raw path (/users/123). Unmatched paths (404s, scanners) collapse into a single __unmatched__ bucket instead of blowing up cardinality.
• Bounded memory. Events are held in a fixed-size in-memory queue; under sustained backpressure, the oldest events are dropped (and counted) rather than growing unbounded or blocking request threads.

Architecture

See ../ARCHITECTURE.md for the full design rationale (why pure ASGI middleware over BaseHTTPMiddleware, why a background thread over asyncio.create_task, why httpx over requests, etc).

Running tests

pip install -e .[dev]
pytest