asyncio worker hits 'Too many open files' after 45 minutes

The code that's running in prod

# scraper_worker.py
# Polls a list of upstream feeds every 60 seconds, parses each
# response, persists deltas. Long-running asyncio worker.

import aiohttp


async def fetch_one(url):
    """Return the response body, or None on any error."""
    session = aiohttp.ClientSession()
    try:
        async with session.get(url) as resp:
            return await resp.text()
    except Exception as e:
        print(f"[ERROR] {url}: {e}")
        return None


async def poll_loop(feeds):
    while True:
        for url in feeds:
            body = await fetch_one(url)
            if body:
                process(body)
        await asyncio.sleep(60)

Log dashboard (last 60 seconds)

Pick the root cause

Four candidates. Three are plausible but mistake symptom for cause. Pick what you'd write in the postmortem timeline.