Ref: https://learn.cantrill.io/courses/1820301/lectures/41301314

• Summary
• Contents:

OS Virtualization - Key Concept

• 🔧 Def: process of running more than one OS on a piece of physical HW or server, without the system crashing
• History: (i) no virtualization → (ii) software virtualization (emulation & para-virtualization) → (iii) hardware virtualization (HW assisted & SR-IOV)
• Amazon EC2 is IaaS (Infrastructure-as-a-Service), which is essentially Virtualization-as-a-Service, or VM-aaS in AWS

OS Virtualization - Historic Evolution

Traditional Infrastructure (No Virtualization)

Diagram: https://github.com/acantril/aws-sa-associate-saac03/blob/main/0900-ELASTIC_COMPUTE_CLOUD(EC2)/00_LEARNINGAIDS/Virtualization101-1.png

• Kernel
  • Small, core part of the OS
  • Runs in privileged mode → can directly interact with HW
• Applications
  • Run in user mode (unprivileged mode) → can't directly interact with HW
  • Need to go through OS to interact with HW → System calls to kernel
• If a non-kernel app tries to directly interact with HW → system-wide error
  • Crash of app or even whole system

First Attempt at OS Virtualization

Diagram: https://github.com/acantril/aws-sa-associate-saac03/blob/main/0900-ELASTIC_COMPUTE_CLOUD(EC2)/00_LEARNINGAIDS/Virtualization101-2.png

• First attempt: use different OSs to run different types of HW
• 👎 Problem: system crashes
  • (back then) CPU could only have one thing running in privileged mode
  • All OSes (in unmodified state) expect to be running in privileged mode

Emulated Virtualization