Card authorization in under 100ms
A latency-budgeted authorization path: cell-based isolation with shuffle sharding, near-caches for account state, and hedged reads — every hop annotated with its share of the 100ms.
What this design does
A card network gives you roughly 100 milliseconds to say yes or no, and it will not wait for your retry storm. This design spends that budget deliberately: a thin router shuffle-shards issuers across isolated cells so one bad tenant can't take the fleet down, account state is served from a two-tier near-cache, and the rare cache miss races two replicas with a hedged read. Every edge label is a line item in the latency budget.
The patterns it composes
- Cell-based architecture — independent cells cap the blast radius of any failure
- Shuffle sharding — each issuer maps to 2 of N cells — noisy neighbors overlap almost nobody
- Near-cache (L1 + L2) — account limits answered in-process ~1ms, distributed cache ~5ms
- Hedged request — cache misses race two replicas; first answer wins
- Deadline propagation — the 100ms budget shrinks at every hop and is enforced, not hoped
Import it, attach your own numbers, and verify the design against failures — or read the engineering notes.