The Kubernetes control plane is one of the two parts of Kubernetes clusters. To refresh your knowledge, Kubernetes is an open source container orchestration system that can automate application deployment, scaling, & management. The other part of the clusters is the nodes or the computing machines.
The control plane is responsible for controlling the cluster. It acts as the central hub of a Kubernetes cluster and manages the cluster state and configuration data. However, the control plane is highly prone to attacks because it is not easy to configure.
Kubernetes Control Plane Components
The Kubernetes control plane consists of multiple components, where each piece manages its own process. These components can run on a single master node or multiple master nodes supporting high-availability clusters.
etcd is a persistent, distributed, and lightweight key-value data store. It is developed by CoreOS that stores the cluster configuration data, representing the overall cluster state at a given point of time. etcd favors consistency over availability in the event of network partitions. This consistency is crucial to maintaining the correct scheduling and operation of services. The K8s API Server uses etcd's watch API in monitoring the cluster and roll out critical configuration changes or restore any divergences of the state of the cluster to what was declared by the deployer.
The API server is a crucial component of the control plane and serves the Kubernetes API using JSON instead of HTTP, providing both internal and external interfaces to Kubernetes. It processes and validates REST requests and updates the state of API objects in etcd, allowing workload and container configuration on worker nodes.
On a control plane, the scheduler is the pluggable component that selects the node an unscheduled pod runs on according to resource availability. The scheduler also tracks resource use on each node to ensure that workload is not scheduled more than the available resources. The scheduler must thoroughly know the resource requirements, availability, and other user constraints and policy directives to ensure this. In essence, the scheduler matches resource supply to workload demand.
The process of controller manager is to manage a set of core Kubernetes controllers. An example of a controller is a Replication Controller, which handles scaling and replication by running a specified number of pod copies through the cluster. It also creates replacement pods in case the underlying node doesn't function. Other controllers include DaemonSet Controller, which runs precisely one pod on every machine, and a Job Controller, which runs pods that run to completion. Label selectors, part of the controller's definition, determines the pod-sets that a controller manages.
Ensuring Stable Container Environments
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