Cloud-Native Microservices With Kubernetes - 2nd Edition

The Control Plane

The Control Plane is composed of several components, each playing a specific role in managing and monitoring the cluster.

Here is a brief description of each component:

API Server (kube-apiserver)

The API Server is the main entry point for interactions with the cluster. It exposes an API that allows users to create, modify, and delete objects in the cluster using a CLI like kubectl, an SDK like client-go, or by calling the API directly.

etcd

etcd is a distributed key-value data storage system used to store the configuration and state of the cluster. Every object in the cluster has a corresponding entry in etcd. etcd is designed to be highly available and fault-tolerant, since it's the source of truth for the cluster. Having a single, reliable source of truth is crucial for the proper functioning of a distributed system in general. In Kubernetes, as in many other distributed systems, this is challenging, and etcd is the component that addresses this challenge.

Controller Manager (kube-controller-manager)

The Controller Manager is responsible for managing Kubernetes controllers. These controllers continuously monitor the state of objects in the cluster and take corrective action to fix any discrepancies and protect the desired state. In other words, controllers ensure that the actual state matches the desired state defined in your manifests.

The Controller Manager runs multiple controller processes as a single binary, including:

• Node Controller: Monitors node health and responds when nodes become unavailable
• ReplicaSet Controller