How to develop custom scheduler plugin

[Seong Moon]

Hi ! Everyone !

I'm very excited to find out the scheduler framework.

Thanks very much to the persons have contributed the scheduler framework.

Now, I'm trying to implement our custom scheduler plugin using the scheduler framework.

But, I can't find any documents for developers like me.

I found the following github hosting out-of-tree scheduler plugins.

https://github.com/kubernetes-sigs/scheduler-plugins

But, there is no detailed documents about how to use and test.

I can't find any place to ask this.

Would you guide me how to start the development of my custom scheduler plugin using the scheduler framework ?

Thanks in advance.

Regards seong.

[Mike Dame]

Hi,

The best way to implement a custom plugin is to write a custom scheduler, which can be done in a few lines of code using the functions NewSchedulerCommand and WithPlugin. This way, the framework will pull in all of the default plugins for you in addition to registering your custom plugin in a simple manageable codebase.

That scheduler-plugins repository is actually itself an example of how to implement custom scheduler plugins with the scheduler framework. It builds an entire custom scheduler and loads in custom plugins using WithPlugin() (see https://github.com/kubernetes-sigs/scheduler-plugins/blob/feee9e705559f3e8746d369cc04a81721c2afe65/cmd/scheduler/main.go#L43-L50).

For more detailed documentation on using the framework, I would recommend reading the enhancement (specifically the section on "out-of-tree plugins": https://github.com/kubernetes/enhancements/blob/master/keps/sig-scheduling/624-scheduling-framework/README.md).

Hope this helps :)

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Mike Dame

Sr. Software Engineer, OpenShift

Red Hat Westford, MA

GitHub: @damemi   

[Aldo Culquicondor]

I would recommend reading https://kubernetes.io/docs/concepts/scheduling-eviction/scheduling-framework/ more than the KEP, to learn about the capabilities of the framework.

And, as already said, the scheduling-plugins repo is a living example on how to write plugins. But I agree that it lacks high level documentation. Feel free to open PRs against it to improve the README.

As for the k8s in-tree plugins, this is the place were we intend to have living documentation https://github.com/kubernetes/kubernetes/blob/master/pkg/scheduler/framework/plugins/README.md

Aldo

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