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Containerization-Orchestration/Kubernetes/1-Information.md

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+# 🚢 Kubernetes (K8s) Documentation
+
+## 🌐 Overview
+**Kubernetes (K8s)** is an open-source container orchestration platform designed to automate the deployment, scaling, and operation of containerized applications.
+
+---
+
+## 🧠 Control Plane (CP)
+The **Control Plane** is the core management component of a Kubernetes cluster. It makes global decisions about the cluster (e.g., scheduling) and maintains the desired state of the cluster by managing workloads and directing communication within the system.
+
+> 💡 **Note:** By default, the Control Plane does not directly manage or run application containers.
+
+### 🔑 Key Components of the Control Plane
+
+- **API Server (`kube-apiserver`)**  
+  Exposes the Kubernetes API and serves as the cluster's entry point. It handles communication between internal components and external clients.
+
+- **Scheduler (`kube-scheduler`)**  
+  Assigns workloads (e.g., Pods) to nodes based on resource availability and defined policies.
+
+- **Controller Manager (`kube-controller-manager`)**  
+  Runs controllers that monitor and regulate the cluster's state, such as the Node Controller and Replication Controller.
+
+- **etcd**  
+  A consistent and highly available key-value store that stores all cluster data, configurations, and state. This is the "database" of Kubernetes.
+
+---
+
+## 🧱 Worker Nodes
+**Worker nodes** are the machines where containerized applications run. Each node contains essential components for managing containers.
+
+### 🔧 Key Components of a Worker Node
+
+- **Kubelet**  
+  An agent that ensures containers run as specified in their Pod definitions. It communicates with the Control Plane to execute assigned tasks.
+
+- **Kube Proxy**  
+  Maintains network rules and manages routing for communication within the cluster and with external systems.
+
+---
+
+## 🔄 Data Flow
+- **Kubelet** and **Kube Proxy** on each worker node interact with the **API Server** to perform operations and update resource states.
+- The **Scheduler** selects suitable nodes for pod placement based on available resources.
+- The **Controller Manager** ensures the actual state of the cluster matches the desired state.
+
+---
+
+## 🛠️ Administration Tools
+
+- **`kubeadm`**  
+  A command-line tool to bootstrap and configure Kubernetes clusters. It streamlines the setup of both the Control Plane and worker nodes.
+
+- **`kubectl`**  
+  The CLI for interacting with the Kubernetes API. It's used to deploy apps, inspect cluster resources, and manage configurations.
+
+---
+
+## 🧩 Kubernetes Version Compatibility
+
+### Kubernetes and Container Runtimes
+
+- **Kubernetes ≤ 1.23**  
+  ✅ Compatible with **Docker** as the default container runtime.
+
+- **Kubernetes 1.24 – 1.25**  
+  ❌ Docker is **not supported** directly. Use `containerd` or another CRI-compliant runtime.
+
+- **Kubernetes ≥ 1.25**  
+  ⚠️ Docker may be installed on the system but must be used **indirectly** through `containerd` or another supported CRI.
+
+---
+
+## 👥 Kubernetes Roles
+
+- **Control Plane (Manager)**  
+  Requires an **odd number** of nodes for high availability (e.g., 1, 3, 5, ...). This ensures quorum in distributed consensus.
+
+- **Worker (none)**  
+  These nodes run application workloads and do not participate in control decisions.
+
+
+image pull policy in kubernetes:
+
+
+example of all work loads:
+https://k8s-examples.container-solutions.com/