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SitePoint17 min readtutorialintermediate

Building ASGI Microservices with Cloudflare Python Workers in Production

Read on sitepoint.com

Summary

Step‑by‑step tutorial for deploying a FastAPI‑based ASGI microservice on Cloudflare Python Workers, covering the Pyodide runtime limits, ASGI bridge, Wrangler setup, pure‑Python dependency handling, KV caching, and a concrete BFF aggregation example.

  • Cloudflare Python Workers run CPython compiled to WebAssembly (Pyodide) – no filesystem, no subprocesses, and no native C extensions unless pre‑compiled by Pyodide.
  • The platform provides a built‑in ASGI bridge: a `fetch` event is translated to ASGI `scope`, `receive`, and `send` callables, eliminating the need for adapters like Mangum.
  • Use `wrangler` to scaffold a Python worker, configure KV bindings, environment vars, and a build command that forces pure‑Python mode for packages like Pydantic (`PYDANTIC_PURE_PYTHON=1`).
  • Prefer pure‑Python, async‑compatible libraries (`httpx` over `requests`, `fastapi`, `pydantic` in pure‑Python mode) because Pyodide cannot load most compiled wheels.

Running ASGI apps at the edge reduces client‑to‑origin latency (p50 ≈ 50 ms vs 200 ms) and enables per‑region aggregation, but the edge runtime imposes strict constraints on dependencies and state. Understanding these limits and the required tooling (Pyodide, Wrangler, KV) is essential for building…

6/10
pythonedgecloudflarefastapiasgiworkers

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