URL Shortener & Link Management Service · View 14 of 23 · Runtime
The two things to notice
- The flow returns at message 4 for most clicks — the cached 302 at the PoP — and everything after it is the minority path.
- The click event is emitted by the edge access log, not by the resolver. That is the single design choice that lets a redirect be cached for 30 seconds without losing a click (ADR-10, ADR-11).
Latency budget
- Cached: p50 ≤ 8 ms, p99 ≤ 20 ms. Resolver hit on L1/L2: p99 ≤ 40 ms. Cold to Cosmos: p99 ≤ 120 ms.
- Coalescing bounds the origin read rate per code per instance to one in flight, which is what makes a viral cold link a latency event rather than a throughput event.
- Hot-set entries carry a 24 h TTL; the edge response carries 30 s. Two TTLs, two different jobs.
What cannot happen here
- No write to the link table, no synchronous call to the management plane, and no dependency on the click pipeline being healthy.
- No credential is held by the resolver, so this flow cannot be turned into a write by any input it receives.
