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arXiv · 2609.20874

Decomposing Predictive Kubernetes Autoscaling for Large Language Model Serving Under Long Startup Delays

Tianrui Liu·Xiaohai Hu
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Abstract

Large language model (LLM) inference deployed on Kubernetes faces an autoscaling challenge that conventional web services do not: new serving replicas take two to ten minutes to start because multi-gigabyte model weights must be loaded, which makes purely reactive scaling structurally late. We ask a sharp question: among the components of a predictive autoscaler, which ones actually matter under such long actuation delays? We answer it by decomposing predictive autoscaling into four factors---token-aware demand tracking, startup-delay lookahead, a bounded uncertainty margin, and plant-state observation---and measuring each factor's contribution in isolation on production-derived heavy-tailed workloads generated by ServeGen. Our main finding is that a simple exponentially weighted moving average (EWMA) predictor with delay-aware lookahead and an upper confidence bound (UCB) margin captures most of the benefit, reducing time-to-first-token (TTFT) service-level-objective (SLO) violations from 53% (reactive, queries-per-second based) to 0.5% across five random seeds; lookahead alone is the single largest factor, a 14$\times$ reduction. Kalman filter variants do not consistently improve the cost--SLO tradeoff. Controlled experiments isolate the reason token granularity is necessary: context length, through key--value cache pressure, degrades TTFT far more than request rate at matched throughput. Finally, a validation on a real Kubernetes cluster (Qwen2.5-7B, A100, vLLM) confirms the central mechanism: a delay-aware lookahead controller cuts TTFT violations from 63.5\% to 3.7\% relative to reactive KEDA scaling. We distinguish throughout which findings are specific to Kubernetes actuation and which are general to LLM serving.

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BibTeXRIS

Tianrui Liu, Xiaohai Hu. 2026-09-16. Decomposing Predictive Kubernetes Autoscaling for Large Language Model Serving Under Long Startup Delays. https://arxiv.org/abs/2609.20874

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