Kube -API Server

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The Kubernetes API server, often referred to as the kube-apiserver, is a critical component of a Kubernetes cluster. It serves as the frontend to the Kubernetes control plane and is responsible for processing RESTful API requests, validating them, and updating the corresponding objects in the cluster's etcd datastore. Here are key aspects of the kube-apiserver:

1. API Endpoints:

  • The kube-apiserver exposes a set of RESTful API endpoints that allow users, operators, and other components to interact with the Kubernetes cluster.
  • These endpoints represent resources such as pods, services, deployments, nodes, etc.

2. RESTful Interface:

  • The API server follows RESTful principles, where resources are identified by URIs (Uniform Resource Identifiers), and standard HTTP methods (GET, POST, PUT, DELETE) are used for operations.

3. Authentication and Authorization:

  • The kube-apiserver handles user authentication using different mechanisms, including client certificates, bearer tokens, and more.
  • Authorization is enforced through Kubernetes RBAC (Role-Based Access Control), which determines what actions a user or a service account is allowed to perform.

4. Admission Control:

  • Admission controllers are plugins that intercept requests to the API server prior to persistence of the object, allowing custom validation and modification.
  • Examples include ResourceQuota, NamespaceLifecycle, and PodSecurityPolicy controllers.

5. API Groups and Versions:

  • Kubernetes organizes its API into groups, and each group can have multiple versions. This helps in maintaining backward compatibility while evolving the API.
  • Common groups include "core" (e.g., /api/v1) and extension APIs (e.g., /apis/apps/v1).

6. etcd Interaction:

  • The kube-apiserver interacts with the etcd datastore to store and retrieve the state of the Kubernetes objects. It uses etcd as a distributed key-value store.

7. High Availability:

  • For high availability, multiple instances of the kube-apiserver can be deployed behind a load balancer. This ensures that the API server remains available even if one instance fails.

8. Secure Communication:

  • Communication with the kube-apiserver is secured using TLS (Transport Layer Security). Clients, including kubectl and other Kubernetes components, use certificates to authenticate with the API server.

9. Auditing:

  • The kube-apiserver can be configured to log API requests for auditing purposes. This helps in tracking who did what in the cluster.

10. Custom Resource Definitions (CRDs):

  • Kubernetes allows users to define custom resources and extend the API by introducing Custom Resource Definitions (CRDs). The kube-apiserver manages these custom resources.

11. API Aggregation Layer:

  • The API server supports aggregation of APIs, allowing third-party APIs to be served alongside core Kubernetes APIs.

12. Extensibility:

  • The kube-apiserver is designed to be extensible, and additional features can be added via plugins and extensions.

13. Health Checks and Readiness Probes:

  • The kube-apiserver exposes health and readiness endpoints for monitoring and self-healing purposes.

14. Dynamic Admission Control:

  • Introduced in newer versions, dynamic admission control allows for the dynamic registration of admission controllers.

The kube-apiserver is the central piece that ties together the Kubernetes control plane components, nodes, and external clients. It is crucial for the proper functioning of a Kubernetes cluster and plays a key role in maintaining the desired state of the system.

 


If you bootstrap your cluster using kubeadmin tool you don't need to know this . But if you setting up the hardway . The the kube API server is available as binary in the kubernetes release page. Download it and configure it to run as a service on your kubernetes master node.


kubeapiserver.service







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