Build a Pastebin-class service: users submit a text / code blob (a "paste"), receive a short URL, share it. Anyone with the URL can read the blob until it expires or is taken down. Visibility ranges from public (search-engine-indexable, edge-cacheable) through unlisted (URL is the secret) to private (owner-only, JWT-authed) and password-protected (server-side check). The system spans an edge CDN, a metadata DB, an object store for bytes, an async abuse pipeline, and a TTL sweeper.

The interview-tier 6-node sketch is wrong here in three load-bearing ways: (1) it under-models the cache-key story for private content; (2) it treats S3 lifecycle as the source of truth for TTL; (3) it puts blob storage on the same Postgres as metadata. We unwind all three.