One of the advantages of using an advanced container orchestration tool like Kubernetes is the flexible scheduler. This provides a wide range of options for users to specify conditions for assigning pods to particular worker nodes that satisfy a condition, and not just based on available resources of the node. In order to explain how Kubernetes makes decisions about placing pods on correct hosts, we can look at the following simplified diagram of a Kubernetes master and a few of its components…
The master API (kube-apiserver) is an instrument that provides read/write access to the cluster’s desired and current state. Components like the scheduler can use the master API to retrieve current state information, apply some logic and calculations, and update the API with new information about the desired state (like specifying to which node a new pod will be scheduled, or which pod should be moved to another node). In addition, cluster users and administrators can update the cluster state or view it through the Kubernetes dashboard, which is a UI that provides access to the API. CI/CD pipelines can also create new resources or modify existing ones using the API.
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