Kubernetes (CKA) - Cluster Architecture & Pod Networking

A Deployment provides declarative updates for Pods and ReplicaSets. It's primarily used for stateless applications, allowing you to describe the desired state of your application and automatically managing the creation, scaling, and updates of Pods.

The Kubernetes Control Plane consists of kube-apiserver, etcd, kube-scheduler, kube-controller-manager, and optionally cloud-controller-manager. These components manage the cluster state and respond to events.

The kube-apiserver is the front end of the Kubernetes control plane. It exposes the Kubernetes API, handles all REST operations, and validates and configures data for API objects like Pods, Services, etc.

etcd is a consistent and highly available key-value store used as Kubernetes' backing store for all cluster data. It stores the entire state of the Kubernetes cluster, including configurations, desired states, and actual states of objects.

The kube-scheduler watches for newly created Pods with no assigned node and selects a node for them to run on. It considers factors like resource requirements, hardware/software/policy constraints, affinity/anti-affinity specifications, and data locality.

The kube-controller-manager runs controller processes. Each controller is a control loop that watches the shared state of the cluster through the API server and makes changes attempting to move the current state towards the desired state. Examples include Node Controller, Replication Controller, Endpoints Controller, and Service Account & Token Controllers.

kubelet is an agent that runs on each node in the cluster. It ensures that containers are running in a Pod. It takes a set of PodSpecs that are provided through various mechanisms and ensures that the containers described in those PodSpecs are healthy and running.

kube-proxy runs on each node and maintains network rules on the node. These rules allow network communication to your Pods from network sessions inside or outside the cluster. It handles service discovery and load balancing for Services by implementing virtual IPs.