Kubernetes_Definition

# Kubernates ?

Open-source container orchestration tool. Developed by Google. Kubernetes helps in managing containers.

# Need for a Tool like this

Trend from Monolith to Microservice architecture.

Monolith = a big, closed application
Microservices = multiple independand services, that communicate with each other

+ Feature	Explanation
High Availability	Application has no downtime
Scalability	Users are balanced
Recovery	Backups & restors

# Architecture / Cluster

Control Plane Node - processes to manage the cluster properly
1. Process: API-Server - Entrypoint to K8s cluster
2. Process: Controller-Manager - what’s happening in cluster?
3. Process: Scheduler - ensures Pods placement
4. Process: etcd - holds state of K8s cluster = can back up & restore
Virtual Network
1. allows a communication between Master-Node & Worker Nodes
Worker Node - applications are running
1. Kubelet-Process - for communicating with other worker nodes

Kubernetes_Definition 2024-11-29 14.23.34.excalidraw
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Excalidraw Data

Text Elements

Master Node “Control Plane”

virtual/physical machine

Worker Node “Node”

App1

App2

Kubelet

Worker Node “Node”

App1

Kubelet

Worker Node “Node”

App1

App2

Kubelet

API-Server

UI

API

CLI

Controller-Manager

Scheduler

etcd

Virtual Network
Link to original

# Load-difference

Worker Nodes

higher workload
much bigger & more resources

Control Plane Nodes

higher importance = backup
not big/many resources

# Main Components

Example: Small database-application

# Node

Server - physical/virtual machine
consists of pods

# Pod

the smallest unit in K8s
managed by Control Plane
in a pod are containers
usually 1 container per pod
each pod - has own IP-address
- Note: Pods die easily - get assigned new IP-address

# Service

is a permanent IP-address for each Pod
if a Pod dies - service + IP-address stay

External Service - open service from external sources

Example: access through internet
BUT: DataBase should relief as Internal Service

# Ingress

First step of request - Ingress, then Service

# Other Components

# ConfigMap

# Secret

# Volume

Storage on local machine.

# Demo-Project

mongo-config.yaml:

apiVersion: v1
kind: ConfigMap
metadata:
  name: mongo-config
data:
  mongo-url: mongo-service

Secret:

Deployment - MongoDB:

Deployment - WebApp:

Terminal:

kubectl apply -f mongo-config.yaml 
kubectl apply -f mongo-secret.yaml
kubectl apply -f mongo.yaml 
kubectl apply -f webapp.yaml 
 
kubectl get all
 
kubectl --help
kubectl get --help
kubectl describe service ...
 
kubectl get svc
minikube ip

Second-Brain

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