Kubernetes Cluster Components, Replication Controller Mechanism, ReplicaSet vs Replication Controller, and kube-proxy Function

Kubernetes Master control plane consists of multiple components that manage and schedule workloads across the cluster.

Kubernetes API Server : the entry point exposing RESTful APIs for creating, reading, updating, and deleting core objects, serving as the central hub for communication between internal components and external clients.

Kubernetes Scheduler : selects appropriate nodes for newly created Pods, handling resource allocation.

Kubernetes Controller Manager : runs various built‑in controllers to ensure the desired state of the cluster.

Replication Controller : ensures a specified number of Pod replicas are running.

Node Controller : monitors node health and marks nodes as healthy or unhealthy.

Namespace Controller : maintains namespaces and cleans up orphaned resources.

Service Controller : manages Services, providing load balancing and service proxying.

Endpoints Controller : keeps Endpoints objects in sync with the Pods backing a Service.

Service Account Controller : creates default ServiceAccounts and associated secrets for each namespace.

Persistent Volume Controller : binds PersistentVolumeClaims to PersistentVolumes and handles reclamation.

DaemonSet Controller : ensures a copy of a Pod runs on every (or selected) node.

Deployment Controller : manages Deployments, which in turn manage ReplicaSets and Pods, handling updates and scaling.

Job Controller : creates Pods that run to completion for one‑time tasks.

Horizontal Pod Autoscaler : automatically scales the number of Pods based on observed metrics.

The Replication Controller (RC) monitors the desired replica count for a set of Pods, creating or deleting Pods to match the specification.

ReplicaSet differs from RC by using label selectors based on sets rather than the older selector mechanism.

kube-proxy runs on each node, watches Service and Endpoint changes from the API server, and programs iptables or IPVS rules to provide virtual IPs and load‑balancing, acting as a transparent proxy for Services.