kubernetes crash course

Code: Yes Created: Mar 21, 2021 3:52 PM Importance: very important Materials: https://www.youtube.com/watch?v=X48VuDVv0do Reviewed: No context: DevOps, kubernetes source: YT

• table of content

intro

orchestration tool for containers

cons

• high availablity or no down time

• scalability

• disaster recovery

k8s components

pod

• smallest unit of k8s, is an abstraction over container
• usually 1 app per pod
• each pod has its own ip
• new ip address on re-creation

service

• permanent ip address can be attached to each pod
• lifecycle of pod and service are not connected
• if pod dies service and ip stay

external service

internal service

ingress

forward requests to services

configmap:

• external conf of your app
• dont put credentials ⚠️

secret:

• like configmap but used for secrets
• used to store secret data
• encoded in base64
• ⚠️ ‼️ built-in securtiy mechanism is not enabled by default
• used data from secret: or configmap: as env variables or properties file

volumes

we can attach either local or remote (outside k8s cluster)

k8s doesn’t manage data persistence you have to manage it explicitly using volumes

replica

• connected to the same service, another node but same service

• service is also load balancer

Deployment:

• you wont create replica for pod but you will define blueprint for the pod which contains how many replica

stateless

statefulSet:

we need DB replica too but we can’t do this using Deployment becuase it has a state (its data)

• for statefull apps
  • mysql
  • elastic search
  • mongo DB
  • etc.
• deploying statefulSet not easy

DB are often hosted outside of K8S cluster

K8S Architecture

worker machine

• node - or server-

• each node has multiple pods

• worker do the actual work

3 processes must be installed on each node

kubelet

• process of k8s itself

• interact with node and pods

• take the config and run the pod inside and assign resources for pods

container runtime

• docker for example

kubeproxy

• foward the requests

• has intellegient forward logic to make it good performance

how to interact with cluster

master node

master processes

1 - api server

• cluster gateway

• acts as a gateway for authentication

• only 1 entrypoint to the cluster

• slide

  

2 - scheduler

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3 - controller manager

4 - etcd(cluster brain)

application data not stored in etcd

• slide

  

we can multiple master nodes

• which have its master processes

• api server is load balanced

• etcd is distributed storage accross all master nodes

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example cluster

• master nodes resources is important but it need less resources bec it has less work load