Phase 2: Hardware, Quantization & Placement · ~60 minutes · Python (stdlib · toy prefix-cache-aware router simulator)
Multi-Region LLM Serving and KV Cache Locality
Round-robin load balancing is actively harmful for cached LLM inference.
Hiring signal: Can operate multi-region llm serving and kv cache locality in production
What you will learn
- Explain why round-robin load balancing breaks cached inference and quantify the TTFT penalty.
- Diagram a cache-aware router: inputs (KV-cache events), algorithm (prefix-hash match), tie-breaker (GPU utilization).
- Name the 32% DR failure driver for LLMs (missing tokenizer files / quantization configs) and state a three-file DR checklist.
- Distinguish commercial cross-region offerings (Bedrock CRI, GKE Multi-Cluster Gateway) from KV-aware routing.
Introduction
A request that does not land on the node holding its prefix pays full prefill cost — roughly 800 ms at P50 on a long prompt versus ~80 ms with a cache hit. In 2026 the production pattern is a cache-aware router (vLLM Router in Rust, llm-d router) that consumes KV-cache events and routes on prefix-hash match. Recent research (GORGO) makes cross-region network latency an explicit term in the routing objective. Commercial "cross-region inference" offerings (Bedrock cross-region inference, GKE multi-cluster gateways) treat inference as opaque — they handle availability, not TTFT. JPMorgan and Mayo Clinic ran us-east-1 failover in Nov 2024 at ~22 minutes. The DR reality: 32% of LLM DR failures are because teams backed up weights but forgot tokenizer files or quantization configs.
Type: Learn Languages: Python (stdlib, toy prefix-cache-aware router simulator) Prerequisites: Phase 17 · 04 (vLLM Serving), Phase 17 · 06 (SGLang RadixAttention) Time: ~60 minutes
Objective
Learning objectives
- Explain why round-robin load balancing breaks cached inference and quantify the TTFT penalty.
- Diagram a cache-aware router: inputs (KV-cache events), algorithm (prefix-hash match), tie-breaker (GPU utilization).
- Name the 32% DR failure driver for LLMs (missing tokenizer files / quantization configs) and state a three-file DR checklist.
- Distinguish commercial cross-region offerings (Bedrock CRI, GKE Multi-Cluster Gateway) from KV-aware routing.
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