The Kubernetes master runs the Scheduler, Controller Manager, API Server and etcd components and is responsible for managing the Kubernetes cluster.
Etcd
Etcd is a distributed, consistent key-value store used for configuration management, service discovery, and coordinating distributed work.
API Server
When you interact with your Kubernetes cluster using the kubectl command-line interface, we are actually communicating with the master API Server component.
Scheduler
The Scheduler watches for unscheduled pods and binds them to nodes via the /binding pod subresource API, according to the availability of the requested resources, quality of service requirements, affinity and anti-affinity specifications, and other constraints.
Controller Manager
The Kubernetes Controller Manager is a daemon that embeds the core control loops (also known as “controllers”) shipped with Kubernetes.