HLD-118·Storage & Media
Easy · 500 ptsChat URL OpenGraph Metadata & Preview Cache
Design a link-unfurling metadata service that caches OpenGraph titles, descriptions, and preview thumbnails when links go viral across messaging channels.
Max p99
≤ 50 ms
Availability
≥ 99.5%
Budget
≤ $2,200
Functional Requirements
- FR-1POST /unfurl — Enqueues or stores extracted OpenGraph metadata for a shared URL.
- FR-2GET /unfurl/{url_hash} — Serves cached title, summary, and thumbnail URL to chat clients.
- FR-3PATCH & DELETE /unfurl/{url_hash} — Updates, revokes, or deletes url_hash entries with bounded TTL or explicit cache/index invalidation.
- FR-4Must absorb viral link storms and isolate 5x backing storage latency spikes.
Workload Profile
Baseline Shares18,000 Read RPS / 1,600 Unfurl Write RPS
Breaking Link Surge53,500 Read RPS / 4,500 Write RPS
Active Working Set14 GB hot URL preview cards
Traffic DistributionStrong Zipfian skew on trending url_hash links
Consistency Model
Eventual metadata refresh acceptable; coalescing prevents duplicate scrapes of viral links.
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