Introducing kube-scheduler-simulator

Introducing kube-scheduler-simulator Motivation Features of the kube-scheduler-simulator The simulator as a better dev cluster What are the use cases? Getting started Getting involved Acknowledgments The Kubernetes Scheduler is a crucial control plane component that determines which node a Pod will run on. Thus, anyone utilizing Kubernetes relies on a scheduler. kube-scheduler-simulator is a simulator for the Kubernetes scheduler, that started as a Google Summer of Code 2021 project developed by me (Kensei Nakada) and later received a lot of contributions. This tool allows users to closely examine the scheduler’s behavior and decisions. It is useful for casual users who employ scheduling constraints (for example, inter-Pod affinity ) and experts who extend the scheduler with custom plugins. The scheduler often appears as a black box, composed of many plugins that each contribute to the scheduling decision-making process from their unique perspectives. Understanding its behavior can be challenging due to the multitude of factors it considers. Even if a Pod appears to be scheduled correctly in a simple test cluster, it might have been scheduled based on different calculations than expected. This discrepancy could lead to unexpected scheduling outcomes when deployed in a large production environment. Also, testing a scheduler is a complex challenge. There are countless patterns of operations executed within a real cluster, making it unfeasible to anticipate every scenario with a finite number of tests. More often than not, bugs are discovered only when the scheduler is deployed in an actual cluster.