how-it-works.md

How the simulator works

This page describes how the simulator works.

0. starts the simulator.

The simulator server works with the HTTP server.

In advance, the simulator needs to launch debuggable-scheduler, etcd, controller-manager and kube-apiserver outside. We recommend using KWOK, see compose.yml to know how we wire things up.

1. users request creating resource.

Users can create resources by communicating with kube-apiserver of KWOK via any clients (e.g. kubectl, k8s client library or Web UI)

2. the scheduler schedules a new pod.

When a new pod is created through kube-apiserver, the scheduler starts scheduling.

3. the results of score/filter plugins are recorded.

Normally, when score/filter plugins are called from scheduler, they will calculate the results and return results to the scheduler. But, in the simulator, custom plugins, that behave as score/filter plugin but records result after calculation, are used in scheduler.

4. the scheduler binds the pod to a node.

The scheduler finally binds the pod to a node if succeeded, or move the pod back to queue if failed.

The result store will notice that the pod has been scheduled/marked as unscheduled by the scheduler and add the scheduling results to the pod's annotation.