The asyncio Mistake That Cost Me 3 Hours

It happened last year when I was adding a “batch domain liveness check” feature to our internal operations platform. The requirement was simple: periodically poll 1000+ domains, check HTTP status codes, and flag any domain as down if it didn’t respond within 5 seconds. I thought to myself — this is clearly an I/O‑bound task. asyncio to the rescue, it should finish in minutes. So I threw in a bunch of async def , await , and gather operations, ran it with full confidence… and the result? 1000 dom