Scheduling

What is Scheduling? 

 

 Process of assigning Pods to Nodes in a Kubernetes cluster. 

 

 

 

 Kubernetes Scheduler: 

 

 The component responsible for deciding which Node a Pod should run on. 

 Works based on the available resources and the Pod's resource requirements. 

 

 

 

 Node Selection: 

 

 Factors considered by the scheduler:

 

 CPU, memory resources. 

 Node affinity. 

 Taints and tolerations. 

 Pod affinity and anti-affinity. 

 Resource requests and limits. 

 

 

 

 

 

 Scheduling Policies: 

 

 Default scheduling behavior. 

 Priority scheduling (priority classes). 

 Custom scheduling policies (e.g., using kube-scheduler with custom rules). 

 

 

 

 Affinity and Anti-Affinity: 

 

 Node Affinity: Constraints that allow or prevent Pods from being scheduled on specific nodes. 

 Pod Affinity: Ensures that Pods are scheduled on nodes where other specific Pods are running. 

 Pod Anti-Affinity: Ensures Pods are not scheduled on the same node as other specified Pods. 

 

 

 

 Taints and Tolerations: 

 

 Taints: Applied to Nodes to prevent Pods from being scheduled unless they tolerate the taint. 

 Tolerations: Allow Pods to be scheduled on Nodes with specific taints. 

 

 

 

 Resource Requests and Limits: 

 

 Requests: Minimum amount of resources a Pod needs (scheduler uses this to place Pods). 

 Limits: Maximum amount of resources a Pod can use (enforced during execution). 

 

 

 

 Preemption: 

 

 When a Pod with higher priority displaces lower-priority Pods to be scheduled. 

 

 

 

 Scheduler Extenders: 

 

 Custom schedulers or extender mechanisms to modify default scheduling decisions. 

 

 

 

 Pod Disruption Budgets (PDB): 

 

 Used to manage voluntary disruptions (like upgrades) to ensure availability during disruptions.