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☸️ Kubernetes (K8s) Architecture & Concepts Guide

A concise and structured reference guide explaining the Kubernetes Cluster Architecture, core components, and operational workflow.

📌 Architecture Overview

Kubernetes operates on a Master-Worker (Control Plane - Node) model:

  • Control Plane (Master Node): The decision-maker. Manages cluster state, scheduling, and overall orchestrations.
  • Worker Nodes: The execution unit. Hosts application containers inside Pods and handles networking.

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🧠 Control Plane (Master Node)

The Control Plane monitors the cluster and ensures the actual state matches the desired state.

Component Description
kube-apiserver The main entryway/gateway for all cluster management (kubectl, REST APIs, Web UI).
etcd A distributed, highly available key-value store holding all cluster data and state configuration.
kube-scheduler Assigns unscheduled Pods to the best available Worker Node based on resource constraints.
kube-controller-manager Runs background controller loops (e.g., Node Controller, ReplicaSet Controller) to maintain cluster health.

⚙️ Worker Node Components

Worker Nodes carry out instructions from the Control Plane and run actual user applications.

Component Description
kubelet The node agent that ensures containers defined in PodSpecs are running and healthy.
kube-proxy The network router on each node that maintains network rules and enables Pod-to-Pod communication.
Container Runtime The underlying software that executes containers (e.g., containerd, CRI-O).
Pod The smallest deployable unit in Kubernetes, containing one or more containers sharing network/storage.

🔄 Deployment Workflow

  [ User / kubectl ]
          │
          ▼
   [ kube-apiserver ] <─────── Writes/Reads ───────> [ etcd ]
          │
     ┌────┴────────────────────────┬────────────────────────┐
     ▼                             ▼                        ▼
[ kube-scheduler ]    [ kube-controller-manager ]     [ Worker Node ]
(Selects best node)       (Maintains state)                 │
                                                            ▼
                                                        [ kubelet ]
                                                            │
                                                            ▼
                                                 [ Container Runtime ]
                                                            │
                                                            ▼
                                                  [ Running Pods ]

🛠️ Key Objects & Concepts

  • Deployment: Defines application updates, scaling, and rollbacks.
  • Service: Provides a stable IP address and DNS name to expose Pods internally or externally.
  • ConfigMap / Secret: Manages configuration data and sensitive credentials separately from application code.
  • Namespace: Virtual clusters used to isolate resources within the same physical cluster.

🚀 Basic Cheat Sheet (kubectl)

# Check cluster information
kubectl cluster-info

# View all running nodes
kubectl get nodes

# Get all running pods in the current namespace
kubectl get pods

# Create a deployment from a manifest
kubectl apply -f deployment.yaml

# Inspect logs of a specific pod
kubectl logs <pod-name>