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VIRTUALIZATION

What it is:

  • Technology that creates isolated virtual versions of computing resources
  • Abstracts physical hardware from software
  • Enables multiple operating systems or applications to run on single physical machine

Problem it solves:

  • Running multiple workloads on dedicated hardware is wasteful and inflexible
  • Without virtualization: need separate physical machines for each application
  • Result: Poor resource utilization, high costs, difficult migration

Hardware vs OS-level Virtualization​

Hardware virtualization (VMs):

  • Each virtual machine runs complete OS with own kernel on top of hypervisor
  • Full isolation between VMs
  • Heavier resource overhead

OS-level virtualization (containers):

  • Multiple isolated user spaces share same kernel
  • Lightweight and fast
  • Can only run applications compatible with host kernel
  • See docker_overview for container details

Key distinction: VMs virtualize hardware (can run different OS types), containers virtualize OS (share kernel).

Hypervisor Types​

Type 1 (Bare Metal):

  • Runs directly on hardware without host OS
  • Examples: VMware ESXi, Hyper-V, KVM, Xen
  • Better performance, lower overhead
  • Used in production data centers and cloud infrastructure

Type 2 (Hosted):

  • Runs on top of host OS
  • Examples: VirtualBox, VMware Workstation, Parallels
  • Easier to set up, more overhead
  • Used for development and testing

Pattern: Type 1 for production workloads and server consolidation. Type 2 for development and desktop virtualization.

VMs vs Containers​

VMs:

  • Full OS per instance, GBs in size, minutes to start
  • Complete kernel isolation
  • Use when need different OS types on same hardware, maximum security isolation, or legacy applications requiring specific OS versions

Containers:

  • Shared kernel, MBs in size, seconds to start
  • Process-level isolation
  • Use when application-level isolation sufficient, need fast startup/scaling, want resource efficiency, or building microservices
  • Covered in docker_overview

Pattern: VMs for OS isolation, containers for application isolation. Or combine: run containers within VMs for both levels.

When to Use VMs​

Use for:

  • Multiple OS environments on single hardware
  • Strong isolation between workloads for security
  • Legacy application support requiring specific OS versions
  • Disaster recovery with snapshots and migration
  • Resource consolidation to reduce hardware costs
  • Dev/test environments isolated from production

Skip for:

  • Performance-critical applications where overhead unacceptable
  • Simple application isolation (containers more lightweight)
  • Resource-constrained environments
  • Bare-metal performance required (GPUs, high-frequency trading)

Key Benefits and Trade-offs​

Benefits:

  • Complete OS isolation
  • Run different OS types on same hardware
  • Strong security boundaries
  • Hardware independence
  • Easy backup/recovery with snapshots
  • Live migration between hosts

Drawbacks:

  • Resource overhead (each VM runs full OS)
  • Slower startup times
  • Larger storage requirements
  • More complex management
  • License costs for guest operating systems

Virtualization in Cloud Computing​

Cloud IaaS built on virtualization:

  • AWS EC2, Azure VMs, Google Compute Engine
  • On-demand virtual machines without managing physical hardware
  • Cloud provider handles hypervisor layer

For container workloads in cloud, see docker_orchestration for managing containerized applications at scale.

Common Pitfalls​

WARNING

Over-provisioning VMs: Allocating too many resources (CPU, RAM) wastes capacity. VMs don't use what they're allocated, they use what they need. Monitor actual usage and right-size allocations.

DANGER

VM sprawl: Unmanaged VM creation leads to wasted resources and security risks. Implement VM lifecycle policies, regular audits, and automated cleanup of unused VMs.

References​