A Kubernetes Scheduler Plugin for Cluster-Wide Placement Optimisation

2026-08-07

AI Summary

This work addresses the limitations of Kubernetes’ default scheduler, which often leads to resource fragmentation and suboptimal utilization due to its local decision-making nature, while existing global scheduling approaches struggle with practical deployment in production clusters. The paper proposes OPSche, the first open-source plugin that collaboratively operates alongside the default scheduler by leveraging the Kubernetes scheduling framework to seamlessly integrate globally optimized schedules generated by external solvers through atomic validation and coordination hooks. OPSche supports three trigger modes—scheduling failure, periodic invocation, and queue stabilization—along with their blocking variants, thereby balancing scheduling quality, latency, and interference without replacing the native scheduler. Experimental results demonstrate that OPSche improves resource utilization by up to 3.0% across diverse cluster configurations and reduces scheduling latency by over one second.

Abstract

The default scheduler of Kubernetes, the state-of-the-art container orchestrator, uses fast, local placement decisions. Unfortunately, this design leads to resource fragmentation, reduced cluster usage, and overprovisioning. External solvers can compute global placement plans, but enforcing these plans in upstream clusters is hard. Kubernetes provides no native cross-node preemption, uncoordinated concurrent scheduling leads to inconsistencies, and replacing the default scheduler would sever deployments from upstream cycles. We present OPSche, an open-source Kubernetes Scheduling Framework plugin where external solvers can drive cluster-wide placement decisions in concert with the default scheduler. OPSche atomically validates and enforces solver-produced plans through coordinated framework hooks and supports three trigger modes: scheduling-failure, periodic, and stable-queue -- resp. triggered when a workload cannot be placed, at fixed time intervals, when the set of pending workloads stabilises. Each mode has a blocking variant for a finer tuning of placement quality, latency, and disruption. We pair OPSche with a constraint-based optimisation solver, showing its feasibility across a broad set of cluster configurations and reporting improvements of resource usage by up to 3.0% and scheduling latency by more than a second.

Problem

• Kubernetes scheduling
• resource fragmentation
• cluster-wide placement
• scheduler plugin
• global optimization

Innovation

• Kubernetes scheduling
• cluster-wide placement
• scheduler plugin
• resource optimization
• constraint-based solver