Ref: https://learn.cantrill.io/courses/2022818/lectures/45640670 =OR= https://learn.cantrill.io/courses/1820301/lectures/42219918 [SAA-C03]

YouTube: https://www.youtube.com/watch?v=ThCD-IZpPdk

• Summary
• Contents:

K8s Concepts

• 🔧 Kubernetes (K8s) = open-source container orchestrastion system
  • Deployment, scaling, and management of containerized apps
  • 💡 Similar to Docker, but with super intelligent robots automating processes
• Cloud agnostic → can be deployed in AWS (Amazon EKS), Azure, GCP, on-premises…

K8s components

• Cluster = a deployment of K8s (includes management & orchestration of the apps)
  • Highly available (HA) cluster of compute resources organized to work as a unit
  • Has a Cluster Control Plane
    • Manages the cluster, scheduling, apps, scaling, healing & deployment
  • Contains 0+ nodes
• Compute units
  • Pod = smallest computing unit in K8s

    • Includes 1+ containers

      💡 “1 pod ↔ 1 container” very common

    • Volatile, non-persistent, ephemeral (not permanent)

    • Shared storage & NWing

    • Run on nodes

  • Node = VM or physical server that functions as a worker in the cluster
    • Collection of compute resources
    • Pods are placed on nodes to run
• Compute app/process definitions
  • Service = single, long-running application
    • runs for long periods on 1+ pods
  • Job = ad-hoc, usually short-lived process
    • creates 1+ pods until completion, then terminates
• Ingress = expose a way into a service
  • Ingress → Routing → Service → 1+ pods
  • Ingress Controller: provides ingress
    • e.g. AWS LB Controller uses ALB/NLB
      • ALB = Application Load Balancer
      • NLB = NW Load Balancer
• Persistent Storage/Volume (PV) = Volume whose lifecycle lives beyond any pod using it
  • 💡 By default storage in K8s is ephemeral

K8s Cluster Structure

• Node components
  • container-runtime (containerd or Docker)
    • SW for handling container operations
  • kubelet-agent
    • agent to interact with the Cluster Control Plane via K8s API
  • kube-proxy
    • NW proxy that coordinates NWing with the control plane
    • configures communication rules with internal or external pods
    • helps implement services
• Cluster Control Plane components
  • kube-apiserver
    • Frontend for K8s control plane
    • Nodes and other cluster elements interact with it via K8s API
    • Can be horizontally scaled for HA & performance
  • kube-scheduler
    • Identifies any pods within the cluster with no assigned node
    • Assigns nodes based on resource requirements, deadlines, affinity/anti-affinity, data locality & any constraints
  • etcd
    • Highly available key-value store
    • Main backing store for the cluster
  • cloud-controller-manager
    • Provides cloud-specific control logic
    • Links K8s with a cloud provider's API (e.g. Amazon EKS)
  • kube-controller-manager (cluster controller processes)
    • Node Controller - monitoring & responding to node outages
    • Job Controller - one-off tasks (jobs) assigned to pods
    • Endpoint Controller - populates endpoints (services ↔ pods)
    • Service Account & Token Controllers - Accounts/API Tokens

K8s Architecture Diagrams