In Kubernetes, the master node is responsible for managing the control plane components and orchestrating the overall operation of the Kubernetes cluster. The master node plays a central role in coordinating and controlling the activities of worker nodes (also known as minions or worker machines) within the cluster.
Here are the key responsibilities of the master node:
- API Server: The master node hosts the Kubernetes API server, which serves as the primary interface for interacting with the Kubernetes control plane. It exposes the Kubernetes API, which users, administrators, and external systems use to create, modify, and delete resources within the cluster.
- Scheduler: The master node contains the Kubernetes scheduler, which is responsible for assigning pods (the smallest deployable units in Kubernetes) to worker nodes based on resource requirements, node capacity, and other constraints. The scheduler ensures that pods are scheduled onto suitable nodes within the cluster.
- Controller Manager: The master node hosts the controller manager, which runs various controllers responsible for maintaining the desired state of resources within the cluster. These controllers include the Node Controller (for managing nodes), Replication Controller (for managing replica sets), Endpoint Controller (for managing service endpoints), and others.
- etcd: The master node typically runs an instance of etcd, a distributed key-value store that serves as the cluster's primary data store. etcd stores configuration data, state information, and metadata about resources within the cluster. It provides a consistent and reliable way to store and retrieve cluster data, ensuring the resilience and consistency of the control plane.
- Cluster-wide Operations: The master node coordinates cluster-wide operations such as deploying applications, scaling workloads, performing rolling updates, and managing network policies. It receives requests from users or automation tools, validates them against cluster policies, and orchestrates the execution of operations across the cluster.
- Authentication and Authorization: The master node handles authentication and authorization for cluster users and components. It verifies the identity of users and services accessing the Kubernetes API, enforces access controls based on roles and permissions, and ensures secure communication within the cluster.
- Health Monitoring and Self-Healing: The master node monitors the health and status of the control plane components and worker nodes within the cluster. It detects failures, performs automatic recovery actions, and ensures the overall health and availability of the Kubernetes cluster.
In summary, the master node in Kubernetes serves as the brain of the cluster, coordinating the activities of worker nodes and ensuring the proper functioning of the control plane components. It provides a centralized management interface, enforces cluster policies, and maintains the desired state of resources within the cluster.
