<b>The CMS hammered by requests for files that didn't exist</b>

<b>The CMS hammered by requests for files that didn't exist</b>

A large documentation site had a broken theme that requested an old sprite image on every page. The file had been deleted, so each request was a 404 — and the CDN, by default, never caches 404s. Every single pageview sent a 404-generating request straight to origin: 2 million wasted origin hits a day for a missing PNG.

Fixing the theme was the real fix, but the deploy was weeks out. So we enabled negative caching: the edge now caches the 404 for 5 minutes instead of asking origin every time.

Origin requests for the dead sprite dropped from 2M to about 280 a day. Origin CPU, which had been pinned at 60% serving error pages, fell to 15%. The fix bought them breathing room until the theme rewrite shipped.

The number that mattered: 2M origin 404s a day down to 280.