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@@ -19,7 +19,7 @@ Kubernetes?**
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**Kensei**: Hi, thanks for the opportunity! I’m Kensei Nakada
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([@sanposhiho](https://github.com/sanposhiho/)), a software engineer at
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[Tetrate.io](https://tetrate.io/). I have been contributing to Kubernetes in my free time for more
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than 3 years, and now I’m an approver of SIG-Scheduling in Kubernetes. Also, I’m a founder/owner of
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than 3 years, and now I’m an approver of SIG Scheduling in Kubernetes. Also, I’m a founder/owner of
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two SIG subprojects,
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[kube-scheduler-simulator](https://github.com/kubernetes-sigs/kube-scheduler-simulator) and
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[kube-scheduler-wasm-extension](https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension).
@@ -32,14 +32,14 @@ brief overview of SIG Scheduling and explain its role within the Kubernetes ecos
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**KN**: As the name implies, our responsibility is to enhance scheduling within
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Kubernetes. Specifically, we develop the components that determine which Node is the best place for
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each Pod. In Kubernetes, our main focus is on maintaining the
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[kube-scheduler](https://kubernetes.io/docs/concepts/scheduling-eviction/kube-scheduler/), along
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[kube-scheduler](/docs/concepts/scheduling-eviction/kube-scheduler/), along
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with other scheduling-related components as part of our SIG subprojects.
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**AP: I see, got it! That makes me curious--what recent innovations or developments has SIG
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Scheduling introduced to Kubernetes scheduling?**
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**KN**: From a feature perspective, there have been [several
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enhancements](https://kubernetes.io/blog/2023/04/17/fine-grained-pod-topology-spread-features-beta/)
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**KN**: From a feature perspective, there have been
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[several enhancements](/blog/2023/04/17/fine-grained-pod-topology-spread-features-beta/)
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to `PodTopologySpread` recently. `PodTopologySpread` is a relatively new feature in the scheduler,
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and we are still in the process of gathering feedback and making improvements.
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@@ -53,59 +53,58 @@ reducing the likelihood of wasting scheduling cycles.
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**A: That sounds interesting! Are there any other interesting topics or projects you are currently
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working on within SIG Scheduling?**
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**KN**: I’m leading the development of `QueueingHint` which I just shared. Given that it’s a big new
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**KN**: I’m leading the development of `QueueingHint` which I just shared. Given that it’s a big new
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challenge for us, we’ve been facing many unexpected challenges, especially around the scalability,
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and we’re trying to solve each of them to eventually enable it by default.
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And also, I believe
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[kube-scheduler-wasm-extention](https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension)
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(SIG sub project) that I started last year would be interesting to many people. Kubernetes has
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[kube-scheduler-wasm-extension](https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension)
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(a SIG subproject) that I started last year would be interesting to many people. Kubernetes has
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various extensions from many components. Traditionally, extensions are provided via webhooks
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([extender](https://github.com/kubernetes/design-proposals-archive/blob/main/scheduling/scheduler_extender.md)
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in the scheduler) or Go SDK ([Scheduling
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Framework](https://kubernetes.io/docs/concepts/scheduling-eviction/scheduling-framework/) in the
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scheduler). However, these come with drawbacks - performance issues with webhooks and the need to
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in the scheduler) or Go SDK ([Scheduling Framework](/docs/concepts/scheduling-eviction/scheduling-framework/)
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in the scheduler). However, these come with drawbacks - performance issues with webhooks and the need to
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rebuild and replace schedulers with Go SDK, posing difficulties for those seeking to extend the
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scheduler but lacking familiarity with it. The project is trying to introduce a new solution to
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scheduler but lacking familiarity with it. The project is trying to introduce a new solution to
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this general challenge - a [WebAssembly](https://webassembly.org/) based extension. Wasm allows
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users to build plugins easily, without worrying about recompiling or replacing their scheduler, and
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sidestepping performance concerns.
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Through this project, sig-scheduling has been learning valuable insights about WebAssembly's
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Through this project, SIG Scheduling has been learning valuable insights about WebAssembly's
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interaction with large Kubernetes objects. And I believe the experience that we’re gaining should be
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useful broadly within the community, beyond sig-scheduling.
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useful broadly within the community, beyond SIG Scheduling.
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**A: Definitely! Now, there are currently 8 subprojects inside SIG Scheduling. Would you like to
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**A: Definitely! Now, there are 8 subprojects inside SIG Scheduling. Would you like to
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talk about them? Are there some interesting contributions by those teams you want to highlight?**
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**KN**: Let me pick up three sub projects; Kueue, KWOK and descheduler.
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**KN**: Let me pick up three subprojects: Kueue, KWOK and descheduler.
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[Kueue](https://github.com/kubernetes-sigs/kueue):
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[Kueue](https://github.com/kubernetes-sigs/kueue)
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: Recently, many people have been trying to manage batch workloads with Kubernetes, and in 2022,
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Kubernetes community founded
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[WG-Batch](https://github.com/kubernetes/community/blob/master/wg-batch/README.md) for better
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support for such batch workloads in Kubernetes. [Kueue](https://github.com/kubernetes-sigs/kueue)
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is a project that takes a crucial role for it. It’s a job queueing controller, deciding when a job
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should wait, when a job should be admitted to start, and when a job should be preempted. Kueue aims
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to be installed on a vanilla Kubernetes cluster while cooperating with existing matured controllers
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(scheduler, cluster-autoscaler, kube-controller-manager, etc).
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[KWOK](https://github.com/kubernetes-sigs/kwok):
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Kubernetes community founded
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[WG-Batch](https://github.com/kubernetes/community/blob/master/wg-batch/README.md) for better
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support for such batch workloads in Kubernetes. [Kueue](https://github.com/kubernetes-sigs/kueue)
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is a project that takes a crucial role for it. It’s a job queueing controller, deciding when a job
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should wait, when a job should be admitted to start, and when a job should be preempted. Kueue aims
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to be installed on a vanilla Kubernetes cluster while cooperating with existing matured controllers
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(scheduler, cluster-autoscaler, kube-controller-manager, etc).
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[KWOK](https://github.com/kubernetes-sigs/kwok)
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: KWOK is a component in which you can create a cluster of thousands of Nodes in seconds. It’s
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mostly useful for simulation/testing as a lightweight cluster, and actually another SIG sub
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project [kube-scheduler-simulator](https://github.com/kubernetes-sigs/kube-scheduler-simulator)
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uses KWOK background.
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[descheduler](https://github.com/kubernetes-sigs/descheduler):
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: Descheduler is a component recreating pods that are running on undesired Nodes. In Kubernetes,
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scheduling constraints (`PodAffinity`, `NodeAffinity`, `PodTopologySpread`, etc) are honored only at
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Pod schedule, but it’s not guaranteed that the contrtaints are kept being satisfied afterwards.
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Descheduler evicts Pods violating their scheduling constraints (or other undesired conditions) so
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that they’re recreated and rescheduled.
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[descheduler](https://github.com/kubernetes-sigs/descheduler)
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: Descheduler is a component recreating pods that are running on undesired Nodes. In Kubernetes,
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scheduling constraints (`PodAffinity`, `NodeAffinity`, `PodTopologySpread`, etc) are honored only at
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Pod schedule, but it’s not guaranteed that the contrtaints are kept being satisfied afterwards.
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Descheduler evicts Pods violating their scheduling constraints (or other undesired conditions) so
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that they’re recreated and rescheduled.
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[Descheduling Framework](https://github.com/kubernetes-sigs/descheduler/blob/master/keps/753-descheduling-framework/README.md).
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: One very interesting on-going project, similar to [Scheduling
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Framework](https://kubernetes.io/docs/concepts/scheduling-eviction/scheduling-framework/) in the
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[Descheduling Framework](https://github.com/kubernetes-sigs/descheduler/blob/master/keps/753-descheduling-framework/README.md)
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: One very interesting on-going project, similar to
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[Scheduling Framework](/docs/concepts/scheduling-eviction/scheduling-framework/) in the
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scheduler, aiming to make descheduling logic extensible and allow maintainers to focus on building
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a core engine of descheduler.
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@@ -125,27 +124,26 @@ improving our components over the years.
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**AP: Kubernetes is a community-driven project. Any recommendations for new contributors or
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beginners looking to get involved and contribute to SIG scheduling? Where should they start?**
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**KN**: Let me start with a general recommendation for contributing to any SIG: a common approach is
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to look for
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**KN**: Let me start with a general recommendation for contributing to any SIG: a common approach is to look for
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[good-first-issue](https://github.com/kubernetes/kubernetes/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22).
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However, you'll soon realize that many people worldwide are trying to contribute to the Kubernetes
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repository.
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I suggest starting by examining the implementation of a component that interests you. If you have
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any questions about it, ask in the corresponding Slack channel (e.g., #sig-scheduling for the
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scheduler, #sig-node for kubelet, etc). Once you have a rough understanding of the implementation,
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scheduler, #sig-node for kubelet, etc). Once you have a rough understanding of the implementation,
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look at issues within the SIG (e.g.,
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[sig-scheduling](https://github.com/kubernetes/kubernetes/issues?q=is%3Aopen+is%3Aissue+label%3Asig%2Fscheduling)),
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where you'll find more unassigned issues compared to good-first-issue ones. You may also want to
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where you'll find more unassigned issues compared to good-first-issue ones. You may also want to
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filter issues with the
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[kind/cleanup](https://github.com/kubernetes/kubernetes/issues?q=is%3Aopen+is%3Aissue++label%3Akind%2Fcleanup+)
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label, which often indicates lower-priority tasks and can be starting points.
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Specifically for SIG Scheduling, you should first understand the [Scheduling
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Framework](https://kubernetes.io/docs/concepts/scheduling-eviction/scheduling-framework/), which is
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the fundamental architecture of kube-scheduler. Most of the implementation is found in
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[pkg/scheduler](https://github.com/kubernetes/kubernetes/tree/master/pkg/scheduler). I suggest
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starting with
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Specifically for SIG Scheduling, you should first understand the
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[Scheduling Framework](/docs/concepts/scheduling-eviction/scheduling-framework/), which is
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the fundamental architecture of kube-scheduler. Most of the implementation is found in
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[pkg/scheduler](https://github.com/kubernetes/kubernetes/tree/master/pkg/scheduler).
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I suggest starting with
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[ScheduleOne](https://github.com/kubernetes/kubernetes/blob/0590bb1ac495ae8af2a573f879408e48800da2c5/pkg/scheduler/schedule_one.go#L66)
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function and then exploring deeper from there.
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significant impact. Despite being called "sub" projects, many have a large number of users and a
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considerable impact on the community.
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And last but not least, remember contributing to the community isn’t just about code. While I
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And last but not least, remember contributing to the community isn’t just about code. While I
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talked a lot about the implementation contribution, there are many ways to contribute, and each one
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is valuable. One comment to an issue, one feedback to an existing feature, one review comment in PR,
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one clarification on the documentation; every small contribution helps drive the Kubernetes
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ecosystem forward.
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**AP: Those are some pretty useful tips! And if I may ask, how do you assist new contributors in
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getting started, and what skills are contributors likely to learn by participating in SIG
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Scheduling?**
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getting started, and what skills are contributors likely to learn by participating in SIG Scheduling?**
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**KN**: Our maintainers are available to answer your questions in the #sig-scheduling Slack
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channel. By participating, you'll gain a deeper understanding of Kubernetes scheduling and have the
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**KN**: Scheduling in Kubernetes can be quite challenging because of the diverse needs of different
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organizations with different business requirements. Supporting all possible use cases in
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kube-scheduler is impossible. Therefore, extensibility is a key focus for us. A few years ago, we
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rearchitected kube-scheduler with [Scheduling
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Framework](https://kubernetes.io/docs/concepts/scheduling-eviction/scheduling-framework/), which
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offers flexible extensibility for users to implement various scheduling needs through plugins. This
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rearchitected kube-scheduler with [Scheduling Framework](/docs/concepts/scheduling-eviction/scheduling-framework/),
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which offers flexible extensibility for users to implement various scheduling needs through plugins. This
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allows maintainers to focus on the core scheduling features and the framework runtime.
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Another major issue is maintaining sufficient scheduling throughput. Typically, a Kubernetes cluster
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unfortunately, we sometimes overlook performance degradation in less common scenarios. It’s
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difficult as even small changes, which look irrelevant to performance, can lead to degradation.
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**AP: What are some upcoming goals or initiatives for SIG Scheduling? How do you envision the SIG evolving in the future?**
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**AP: What are some upcoming goals or initiatives for SIG Scheduling? How do you envision the SIG evolving in the future?**
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**KN**: Our primary goal is always to build and maintain _extensible_ and _stable_ scheduling
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runtime, and I bet this goal will remain unchanged forever.
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As already mentioned, extensibility is key to solving the challenge of the diverse needs of
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scheduling. Rather than trying to support every different use case directly in kube-scheduler, we
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will continue to focus on enhancing extensibility so that it can accommodate various use
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cases. [kube-scheduler-wasm-extention](https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension)
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cases. [kube-scheduler-wasm-extension](https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension)
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that I mentioned is also part of this initiative.
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Regarding stability, introducing new optimizations like QueueHint is one of our
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**KN**: Scheduling is one of the most complicated areas in Kubernetes, and you may find it difficult
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at first. But, as I shared earlier, you can find many opportunities for contributions, and many
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maintainers are willing to help you understand things. We know your unique perspective and skills
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are what makes our open source so powerful :)
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are what makes our open source so powerful 😊
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Feel free to reach out to us in Slack
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([#sig-scheduling](https://kubernetes.slack.com/archives/C09TP78DV)) or

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