Kubernetes
Posted inContainers

Kubernetes

Kubernetes (often abbreviated as K8s) is an open-source platform designed to automate the deployment, scaling, and management of containerized applications.

It was originally developed by Google and is now maintained by the Cloud Native Computing Foundation. Modern applications are built using containers (e.g., Docker), but managing hundreds or thousands of containers manually is complex.

Kubernetes solves this by acting as a container orchestrator, helping you:

Balance load across instances

Deploy applications easily

Scale up/down automatically

Handle failures (self-healing)

Expose services to users

Architecture

A Kubernetes cluster has two main parts:

1. Control Plane (Brain)

Manages the cluster.

These components make decisions and maintain the desired state.

API Server (kube-apiserver)

  • Entry point to Kubernetes
  • All commands (kubectl) go here
  • Validates and processes requests

Think: Front door of the cluster

etcd

  • Distributed key-value database
  • Stores entire cluster state
  • Highly critical component

Think: Cluster’s brain memory

Scheduler (kube-scheduler)

  • Decides which node runs a pod
  • Based on:
    • CPU/memory
    • affinity/anti-affinity
    • taints/tolerations

Think: Placement engine

Controller Manager (kube-controller-manager)

  • Runs controllers that maintain desired state
  • Examples:
    • Node controller
    • Replication controller
    • Endpoint controller

Think: Auto-correction system

Cloud Controller Manager (optional)

  • Integrates with cloud providers (AWS, Azure, GCP)
  • Manages:
    • Load balancers
    • Storage
    • Nodes

2. Worker Nodes (Muscle)

Run your applications (containers).

These run your actual workloads.

Kubelet

  • Agent running on each node
  • Talks to API server
  • Ensures containers are running correctly

Think: Node supervisor

Container Runtime

  • Runs containers
  • Examples:
    • Docker
    • containerd
    • CRI-O

Think: Engine that runs containers

Kube Proxy

  • Handles networking
  • Manages service routing and load balancing

Think: Traffic manager

🔹 Pods

  • Smallest deployable unit
  • One or more containers

Think: Your actual application

3. Networking Layer

Kubernetes networking connects everything:

  • Pod-to-Pod communication
  • Service abstraction
  • External access

Key concepts:

  • Cluster IP
  • NodePort
  • LoadBalancer
  • Ingress

Cluster & Context

kubectl cluster-info
kubectl version
kubectl config view
kubectl config current-context
kubectl config get-contexts
kubectl config use-context <context-name>
kubectl config set-context --current --namespace="<name-space>"

Get Resources

kubectl get pods
kubectl get nodes
kubectl get services
kubectl get deployments
kubectl get replicasets
kubectl get namespaces
kubectl get events

With extra options:

kubectl get pods -o wide
kubectl get pods -A
kubectl get all

Describe

kubectl describe pod <pod-name>
kubectl describe node <node-name>
kubectl describe deployment <deployment-name>
kubectl describe service <service-name>

Logs

kubectl logs <pod-name>
kubectl logs <pod-name> -c <container-name>
kubectl logs -f <pod-name>   # follow logs
kubectl logs --previous <pod-name>

Create / Apply / Delete

kubectl apply -f file.yaml
kubectl create -f file.yaml
kubectl delete -f file.yaml
kubectl delete pod <pod-name>
kubectl delete deployment <deployment-name>
kubectl run nginx --image=nginx
kubectl create deployment myapp --image=nginx
kubectl expose deployment myapp --type=NodePort --port=80

Edit & Patch

kubectl edit deployment <name>
kubectl patch deployment <name> -p '{"spec":{"replicas":3}}'

Scaling

kubectl scale deployment <name> --replicas=3

Rollouts (Deployments)

kubectl rollout status deployment <name>
kubectl rollout history deployment <name>
kubectl rollout undo deployment <name>
kubectl rollout restart deployment <name>

Exec & Debugging

kubectl exec -it <pod-name> -- /bin/bash
kubectl exec -it <pod-name> -- /bin/sh

Copy Files

kubectl cp <pod-name>:/path/file ./file
kubectl cp ./file <pod-name>:/path/file

Port Forwarding

kubectl port-forward pod/<pod-name> 8080:80
kubectl port-forward svc/<service-name> 8080:80

Namespaces

kubectl create namespace dev
kubectl get ns
kubectl config set-context --current --namespace=dev

ConfigMaps & Secrets

kubectl create configmap my-config --from-literal=key=value
kubectl create secret generic my-secret --from-literal=password=1234

kubectl get configmaps
kubectl get secrets

Resource Usage (Metrics)

kubectl top nodes
kubectl top pods

Explain

kubectl explain pod
kubectl explain deployment.spec