Edge Caching at Scale with Cache Tags

We cache aggressively at the edge. The trick was never the cache — it was purging it precisely when data changed.

Tag, then purge by tag

Attach tags to a response, then invalidate by tag when the underlying data mutates:

res.setHeader("Cache-Tag", "product-42,catalog");
// later, when product 42 changes:
await purgeByTag("product-42");

The goal is to purge exactly what changed. Purge too much and you've built a slow uncached site with extra steps.