PATTERN Cited by 1 source

Latency-probe-based topology

Pattern

Build and maintain a CDN cache hierarchy dynamically by continuously probing the latency from every edge data center to every origin, and using the resulting latency map to select optimal routing paths — rather than statically assigning edges to tiers by geographic proximity or manual configuration.

Shape

┌─────────────────────────────────────────────┐
│ Continuous probing (every 15 min)           │
│   Every DC → every known origin IP          │
│   → latency matrix (DC × Origin)            │
└──────────────────────┬──────────────────────┘
                       │
                       ▼
┌─────────────────────────────────────────────┐
│ Topology builder                            │
│   For each origin:                          │
│   - Find DC with lowest latency → primary   │
│   - Find DC with next-best + PoP diversity  │
│     → fallback                              │
└──────────────────────┬──────────────────────┘
                       │
                       ▼
┌─────────────────────────────────────────────┐
│ Routing layer                               │
│   Edge miss → primary upper tier → origin   │
│   Primary down → fallback → origin          │
└─────────────────────────────────────────────┘

Properties

• Adapts to network changes: new peering, fiber cuts, or provider changes are reflected within one probe cycle.
• No manual topology maintenance: operators don't maintain edge-to-tier mappings.
• Origin-aware: each origin gets its own optimal topology (unlike static per-region assignment).

Failure Modes

• Anycast origins: probing becomes unreliable → mitigated by concepts/anycast-origin-detection and patterns/region-hint-for-anycast-origins.
• Probe noise: short-lived latency spikes could cause topology flapping → smoothed by aggregation/hysteresis (implementation detail not disclosed).

Seen in

• sources/2026-07-10-cloudflare-improving-smart-tiered-cache-for-public-cloud-regions — Smart Tiered Cache's probe-driven topology