Defines what Kubernetes scheduler is and discuss how it works and then there is a demo on features of Kubenetes scheduler.

1. How Kubernetes
Scheduler works
Himani Agrawal
@himani_93

2. Agenda
● Scheduling in Kubernetes
● Scheduler use cases
● How it works?
● Demo
● New in scheduler

3. Credits: Julia Evans (@b0rk)

4. In Kubernetes, scheduling
refers to making sure that
Pods are matched to Nodes
so that Kubelet can run
them.
Ref: https://kubernetes.io/docs/concepts/scheduling/kube-scheduler/

5. Credits: https://cloud.google.com/kubernetes-engine/kubernetes-comic/

6. What can be achieved through scheduler?
● Ensure pods gets required resources
● Prioritize workload
● Configure geographical distance
● Reserve nodes for specific pods

7. Credits: https://cloud.google.com/kubernetes-engine/kubernetes-comic/

8. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run Assign the pod to the node

9. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run Assign the pod to the node

10. Scheduler is basically
a Kubernetes
Controller

11. Kubernetes Controller
Current state Takes necessary actions
so that desired state is
achieved
Once desired state is
achieved, it updates the
state of resources
This continuously runs in a loop
Credits: LEGO

12. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run Assign the pod to the node

13. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run
Fi2
Assign the pod to the node
a Filtering

14. Filtering
4 5 6
1 2 3

15. Pod manifest
apiVersion: "v1"
kind: Pod
metadata:
name: sansa
spec:
nodeName: ""
containers:
image: busybox

16. Filtering
4 5 6
2 31

17. Filtering
4 5 6
2 31

19. 4 5 6
1 2 3

20. 4 5 6
1 2 3
10
7 8 9

21. 4 5 6
1 2 3
10
7 8 9

22. 4 5 6
1 2 3
10
7 8 9

23. 4 5 6
1 2 3
10
7 8 9

24. 4 5 6
1 2 3
10
7 8 9

25. 4 5 6
1 2 3
10
7 8 9

26. percentageOfNodesToScore

27. 4 5 6
1 2 3
10
7 8 9

28. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run
Fi2
Assign the pod to the node
a Filtering
b Scoring

29. 3
1
2
8

30. What scheduler needs?
1 2 3
Need to know a pod is NOT
assigned to a node
Choose a best fit node on
which the pod can run Assign the pod to the node

31. Binding
apiVersion: "v1"
kind: Pod
metadata:
name: sansa
spec:
nodeName: "8"
containers:
image: busybox

32. API Server Scheduler Kubelet
create pod
watch (create pod)
create binding
watch (create bind)
Container
Engine
create container
apiVersion: "v1"
kind: Pod
metadata:
name: sansa
spec:
image: busybox
Pod Manifest
How event triggering happens?

33. Demo
Picture Credits: Ashley McNamara

34. Demo
● nodeSelector
● nodeAffinity
● podAffinity
● taints and tolerations

35. What else?
● Extensible, https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/
● Custom Scheduler, https://kubernetes.io/docs/tasks/administer-cluster/configure-multiple-schedulers/
● Even Pod Spreading, https://github.com/kubernetes/enhancements/blob/master/keps/sig-
scheduling/20190221-even-pods-spreading.md
● Scheduling Framework, https://github.com/kubernetes/enhancements/blob/master/keps/sig-
scheduling/20180409-scheduling-framework.md
● Batch Scheduling
https://github.com/kubernetes/enhancements/blob/master/keps/sig-scheduling/34-20180703-
coscheduling.md

36. References
● Kubernetes Community Docs
● https://jvns.ca/blog/2017/07/27/how-does-the-kubernetes-scheduler-work/
● What Happens when k8s

37. Getting Involved
➔ Github Repo
https://github.com/kubernetes/kubernetes/tree/master/pkg/s
cheduler
➔ Mailing List: kubernetes-sig-scheduling
https://groups.google.com/forum/#!forum/kubernetes-sig-
scheduling
➔ Slack: #sig-scheduling
https://kubernetes.slack.com/messages/C8TSNPY4T

38. Merci beaucoup
@himani_93