Hypervisors

Topic: Hypervisors Deep Dive

The hypervisor, also known as the Virtual Machine Monitor (VMM), is the critical layer of software that makes virtualization possible.

Role: It sits between the physical hardware and the virtual machines.
Function: It creates a virtualization layer that abstracts the physical hardware resources (CPU, Memory, Storage) and distributes them to the VMs.
Isolation: It ensures that VMs are isolated from each other and from the host system, so a crash in one VM does not affect others.

Type 1 hypervisors are installed directly on the physical server's hardware. There is no underlying operating system required to run them.

Structure: Hardware -> Hypervisor -> Virtual Machines.
Performance: High. They have direct access to hardware and act as their own operating system, managing and scheduling resources directly.
Use Case: Enterprise data centers, cloud infrastructure (AWS, Azure), large-scale server consolidation.
Examples:
VMware ESXi
Microsoft Hyper-V (Server)
Xen
KVM (Kernel-based Virtual Machine) - Note: KVM turns the Linux kernel itself into a Type 1 hypervisor.
Less Common Use Case: Hypervisor Security Hardening: Discuss techniques like disabling unnecessary services on Type 1 hypervisors and ensuring management access uses secure protocols (SSH/TLS) only.

Type 2 hypervisors run as an application on top of a conventional operating system (the Host OS).

Structure: Hardware -> Host OS -> Hypervisor App -> Virtual Machines.
Performance: Lower than Type 1. The hypervisor does not have direct hardware access. All hardware requests, including CPU and memory access, must be passed to the Host OS's scheduler first. This extra layer of translation adds overhead and latency.
Use Case: Desktop virtualization, development/testing environments, running a second OS on your laptop.
Examples:
Oracle VirtualBox
VMware Workstation Pro / Player
Parallels Desktop (for Mac)

Virtualization is not magic; it relies on the host CPU's architecture. The guest operating system's architecture must be compatible with the host's.

x86-64 (or amd64): The dominant architecture for modern desktops, laptops, and servers. You can virtualize 64-bit (x86-64) and 32-bit (x86) operating systems on a standard 64-bit computer.
ARM: The architecture for most mobile devices and Apple Silicon Macs. You cannot directly virtualize an x86 OS on an ARM host. This requires emulation, a much slower process where every CPU instruction is translated in software.
Key Takeaway: Virtualization shares hardware. Emulation fakes it.
Advanced Topic: Nested Virtualization: Explain that running a hypervisor inside a VM (e.g., running Hyper-V inside a KVM guest) requires specific CPU extensions (VT-x/AMD-V must be exposed to the guest) and incurs a significant performance penalty.

For this course, we will use Oracle VM VirtualBox, a popular open-source Type 2 hypervisor.

Cross-Platform: Runs on Windows, Linux, and macOS hosts.
Key Components:
VirtualBox Manager: The GUI for creating and managing VMs.
VBoxManage: A powerful CLI tool for advanced management.
Extension Pack: Adds features like USB 2.0/3.0 support, VRDP (Virtual Remote Desktop Protocol), and other advanced capabilities.

Installation:
Download and install VirtualBox on your workstation.
Optional but Recommended: Install the VirtualBox Extension Pack.
Explore Global Preferences:
Open VirtualBox and go to File > Preferences.
Check the Default Machine Folder. Ensure this drive has plenty of free space.
Network Host Manager:
Go to File > Tools > Network Manager.
Observe any "Host-Only Ethernet Adapters" listed. We will use these in future sessions.

Advanced Task: Using the VBoxManage CLI tool (introduced in the Key Components section), attempt to list all virtual networks available on the host using VBoxManage list natnets or VBoxManage list hostonlyifs. This demonstrates interacting with the hypervisor outside the GUI.