Architecture of Kubernetes

Kubernetes, also known as k8s, is an open-source container orchestration platform that manages Docker containers in the form of a cluster. The Kubernetes architecture consists of a master node (control plane) and multiple worker nodes (data plane).

Control Plane Components

1. API Server: The core component of Kubernetes that resides on the master node. Acts as the gateway between the Kubernetes cluster and the external world, exposing Kubernetes functionalities through RESTful APIs. Handles requests for operations such as deploying applications, scaling workloads, or retrieving cluster information.
2. Scheduler: Responsible for scheduling pods or resources to worker nodes. Uses information from the API server to decide which node is best suited for a given workload, taking factors like resource availability and constraints into account.
3. Controller Manager: Ensures that the desired state of the cluster, as defined in configurations (e.g., YAML files), is maintained. Manages tasks such as maintaining replicas of pods (via ReplicaSets), handling node failures, and ensuring persistent storage is bound to the correct pods.
4. etcd: A distributed key-value store that serves as Kubernetes' database. Stores all cluster data, including configurations and the current state of the cluster. Acts as a backup and ensures consistency across the cluster.
5. Cloud Controller Manager: An optional component used for integrating Kubernetes with cloud providers. Manages cloud-specific services such as load balancers, storage provisioning, and network routes.

Data Plane Components

1. Kubelet: A Kubernetes agent running on each worker node. Responsible for pod lifecycle management and ensuring the containers in a pod are running as expected.
2. Container Runtime: Enables containers to run on a node. Examples include Docker, containerd, and CRI-O.
3. Kube-proxy: A network proxy that manages networking rules on worker nodes. Assigns IP addresses to pods and handles load balancing for services within the cluster.

Real-World Example
Imagine an e-commerce platform like Amazon that handles millions of users daily. Kubernetes can be used to:
• Deploy microservices for user authentication, product catalogs, and payment systems.
• Scale workloads automatically during peak shopping seasons.
• Ensure high availability by replicating critical services across multiple worker nodes.
• Handle rolling updates and rollbacks seamlessly for new features or fixes.
Diagram
Below is a simplified representation of the Kubernetes architecture:

Additional Notes
• Pods are the smallest deployable units in Kubernetes and represent a single instance of a running process in a cluster. A pod can contain one or more containers.
• The control plane ensures that the cluster operates as intended, while the data plane performs the actual work of running containers and providing networking.
Kubernetes’ architecture enables it to manage complex containerized applications with high availability, scalability, and resilience.