How to work the kube-scheduler 

The Kubernetes Scheduler (kube-scheduler) is responsible for assigning pods to nodes in the cluster based on various factors such as resource requirements, affinity/anti-affinity rules, node capacity, and user-defined constraints. Here’s how the kube-scheduler works:

• Pod Creation Request: When a user submits a request to create a pod, either through the Kubernetes API server or via a higher-level resource such as a Deployment or ReplicaSet, the request is initially received by the kube-API Server.

• Pod Information:
  • The kube-API Server forwards the pod creation request to the kube-scheduler component.

• Scheduling Decision:
  • The kube-scheduler evaluates various factors to determine the best node for placing the pod. These factors include:
    • Resource requirements: CPU and memory requests/limits specified in the pod’s configuration.
    • Node affinity/anti-affinity rules: Constraints that dictate pod placement based on node labels or other attributes.
    • Pod tolerations: Specifications that allow pods to be scheduled on nodes with certain taints.
    • Node capacity: The available resources (CPU, memory) on each node in the cluster.
    • Pod inter-dependencies: Requirements for co-locating or spreading pods across different nodes.
    • Custom scheduling policies: User-defined rules or preferences for pod placement.

• Node Selection:
  • Based on the evaluation of these factors, the kube-scheduler selects the most suitable node for placing the pod.

• Binding:
  • Once a node is selected, the kube-scheduler updates the pod’s configuration to specify the selected node as its target node. This process is known as “binding.”

• Communication:
  • The kube-scheduler communicates the scheduling decision back to the kube-API Server.

• Pod Deployment:
  • The kube-API Server updates the pod’s configuration in the ETCD cluster to reflect the scheduling decision.

• Pod Creation:
  • The kubelet running on the selected node receives the pod’s configuration from the kube-API Server.
  • The kubelet pulls the required container images, creates the pod, and starts the containers on the node.

• Status Update:
  • Once the pod is successfully deployed on the node, the kubelet updates the pod’s status in the ETCD cluster via the kube-API Server.

• Continuous Monitoring:
  • The kube-scheduler continuously monitors the cluster for new pod creation requests and repeats the scheduling process as needed.

By following this process, the kube-scheduler ensures efficient and optimal utilization of cluster resources while meeting the requirements and constraints specified by users and administrators.