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Kubernetes Crash Course for Absolute Beginners

0:00 - Intro and Course Overview

Overview

Part 1. Introdunction to k8s

  1. What is k8s
    • why do we need it.
    • why did it become polular.
  2. k8s Architecture
    • How they works in background

Part 2. Main k8s Components

  • Pod
  • Volume
  • Service
  • Ingress
  • ConfigMap
  • Deployment
  • Secret
  • StatefulSet
  • DaemonSet

Part 3. Local Setup

Part 4. Demo Project

k8s is very popular & complex

1:44 - What is Kubernetes

Official def. of k8s

  • Open source container orchestration tool
  • Devoped by Google
  • Helps manage containerized apps in diffrent deploy environment.

What prbls k8s solves?
What are the tasks of an orch. tools?

  • Neeed for con. orch. tool
    • Trend from Monolith to Microservices.
    • Increase usage of (small,independent) con.
    • Demand for a proper way of managing those hunds of con.

What features orch tools offer?

  1. High Availability or no downtime
  2. Scalability or high performance
  3. Disaster recovery - backup&restore
4:33 - Kubernetes Architecture

kubarch

at least one Master node (Virtual/Physical)

  • several k8s processes
    • necessary to run&manage the cluster
  • API server
    • Entrypoint to k8s cluster
      • UI: Dashboard, etc
      • API: scripts&automating
      • CLI
  • Controller Manager
    • Keep track of happenings in cluster
  • Scheduler
    • ensures Pods placement
    • Scheduler decides on which node new pod should be scheduled based on Load
  • etcd storage
    • k8s backing store

Virtual Network

  • Master and Workers talks on N/W
  • Creates 1 unified mach. inside of a cluster

several Worker nodes

  • a kubelet process
    • kubelet: k8s process that communic8s each nodes&excutes some commands
  • containers of diffrent apps
    • the place that apps r running
Master Worker
small master processes Higher workload
IMPORTANT bigger&more resources
Need Redundance -
8:58 - Main K8s Components
09:29 - Node & Pod

pod

Pod

  • Smallest unit in k8s
  • Abstraction over container
    • Top layer of image
  • Usually 1 app per Pod
  • Each Pod get its own IP addr
    • talks using internal IP
  • Ephemeral
  • New IP addr on re-creation
    • Inconvenient based on IP structure
12:19 - Service & Ingress

service

Service

  • Permanent IP addr
  • Lifecycle of Pod and Service NOT CONNECTED
  • Specify the type of Service on creation
    • Internal Service = Default
    • External Service
      • user can access app on web browser
    • Internal Service
      • user cannot access db

Ingress

  • node-ip:port 주소 형식은 실제 사용엔 무리가 있음
  • 일종의 도메인서버역할인듯?
  • my-app.com 식으로 전환
14:31 - ConfigMap & Secret

var

Database URL usually in the BUILT apps

  • If u change the DB Endpoint
    • Rebuild the image
    • Push it to repo
    • Pull it in Pod
    • Restart whole procedure

ConfigMap

  • External conf. of apps
    • DB_URL
    • DB Servicename
    • DB username
    • DB password
  • ConfigMap is for non-credential data only!

Secrets

  • Used to store secret data
  • Reference Secret in Deployment/Pod

Use it as environment variables or as a properties file

17:52 - Volume

Volume

  • Storage on local machine
  • Or remote, outside of k8s cluster (on cloud or another server)
  • Data persistence
    • If not, when cluster is restarted, all data(DB,Logs) be gone.
  • k8s cluters basically do not manage data persistence
19:46 - Deployment & StatefulSet

dply&sts

Deployment stage

  • In order to avoid downtime,
  • Replicate everything on different server
  • Replica or Clone is connected to same service
  • Service
    • Permanent IP
    • Load balancer
  • Define blueprint for Pods
    • Specify how many replicas

DEPLOYMENT

  • Blueprint for “my-app”Pods
  • You create Deployments
  • Abstraction of Pods

DB can’t be replicated via Deployment

  • to avoid Data inconsistance

STATEFULSET

  • for STATEFUL apps like mysql,elasticsearch,mongodb

Deployment = for stateLESS Apps
StatefulSet = for stateFUL Apps or Databases

Deploying StatefulSet is challenge(not easy)

  • DB are often hosted outside of k8s cluster
  • k8s cluster communi8s external DB
Wrap up
  • Pod
    • abstraction of containers
  • Service
    • Communication
  • Ingress
    • Route traffic into cluster
  • ConfigMap & Secret
    • external configuration
  • Volume
    • Data Persistence
  • Deployment & StatefulSet
    • Replication the cluster
26:28 - Kubernetes Configuration

K8s conf.

  • Master node
    • CLI
      • kubectl
    • API
      • YAML, json
      • Deployment = a tempalte for creating pods
        • replica, container(image),env,prot
      • Declarative
      • (Actual state) Is == (Desired State) Should

conf

Each Conf. File has 3 Parts

  1. metadata
    • name, labels, …
  2. specification
    • replicas, selector, template / ports, env, …
    • attibutes of “spec” are specific to the kind(Depl/Serv)
  3. status
    • Automatically generated and added by k8s
    • Compare ‘Desired’ = ‘Actual’?
    • k8s updates status continuously

Where does k8s get 3. status data?

  • from etcd
    • Etch holds the current status of any k8s component

Format of Conf. File

  • YAML
  • human friendly data serialization standard 4 all prgm Lang.
  • syntax: Strict indentation!
  • store the conf file w/code version tool(git)
32:39 - Minikube and Kubectl - Setup K8s cluster locally

Production Cluster Setup

  • Multiple Master & Worker nodes
  • Separate virtual or physical machines
  • Test on local machine?

Minikube

  • Master and Node processes run on ONE mach.
  • Docker pre-installed

Kubectl

  • command line tool for k8s cluster
  • Most powerful among UI, API, CLI(=kubectl)
  • Can interacts w/Cloud cluster

설치과정은 Mac용이야 흑흑

kubectl CLI > for conf. the Minikube cluster Minikube CLI > for start up/delte the cluster

41:17 - Complete Demo Project: Deploy WebApp with MongoDB

demo

k8s Components Overview

  • Create 4 k8s conf files
    • ConfigMap; MongoDB Endpoint
    • Secret; MongoDB User & Pwd
    • Deployment\&Service; MongoDB App w/Internal Service
    • Deployment\&Service; Wepapp w/External Service
# mongo config

##### 1:05:40 - Interacting with Kubernetes Cluster


##### 1:11:03 - Congrats! You made it to the end 🎉



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