Virtualization

Last Updated: 2024-07-24

Hyperconverged Infrastructure (HCI)

Your resources: compute, storage, networking.

HCI: uses software to abstract, pool and manage those resources. (i.e. just another term for virtualized / software-defined compute, storage and networking.)

• virtualized computing: hypervisor
• virtualized storage: software defined storage (SDS)
• virtualized networking: software defined networking (SDN)

Computation / Server Virtualization

3 kinds:

• Full Virtualization (HVM): uses a hypervisor, which directly communicates with a physical server's disk space and CPU. Each virtual server is independent and unaware of the other virtual servers.
• Para-Virtualization (PV): uses a hypervisor, each OS on the virtual servers is aware of one another.
• OS-Level Virtualization (Containers): does not use a hypervisor. The virtualization capability is part of the physical server OS (e.g. cgroup).

Hypervisor

Hypervisor = Virtual Machine Manager (VMM).

2 Types:

• Type-1: native or bare metal hypervisor.
  • hypervisor runs directly on the host's hardware.
  • e.g. XEN, Hyper-V (Windows; used by WSL), VMware ESXi (renamed from ESX; i for integrated)
• Type-2: hosted hypervisor.
  • hypervisor runs on a conventional operating system, a guest operating system runs as a process on the host.
  • e.g. VMware Workstation, VirtualBox, QEMU.

KVM can be considered as both Type-1 and Type-2.

Some of the most popular hypervisors:

• Xen: an external hypervisor; it assumes control of the machine and divides resources among guests.
• KVM: part of Linux and uses the regular Linux scheduler and memory management. This means that KVM is much smaller and simpler to use; it also provides some features not available in Xen. For example, KVM can swap guests to disk in order to free RAM.
  • It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko.
  • QEMU is the default VMM (Virtual Machine Manager) of KVM, but can be replaced. QEMU is a generic and open source machine emulator and virtualizer. The Android emulator is built on QEMU.
  • KVM: kernel side; QEMU: userspace. QEMU can use KVM and host CPU to accelerate: $ qemu-system-x86_64 accel=kvm ...
  • The kernel component of KVM is included in mainline Linux, as of 2.6.20. The userspace component of KVM is included in mainline QEMU, as of 1.3.
• VirtualBox: by Oracle
  • a Type 2 Hypervisor.
  • open source and free; No hardware virtualisation required.
• Cloud Hypervisor: a special-purposed VMM, doesn't aim to be a all-functioning emulator (like QEMU), but only concerns the use case of cloud workloads.
  • "Cloud Hypervisor is an open source Virtual Machine Monitor (VMM) implemented in Rust that focuses on running modern, cloud workloads, with minimal hardware emulation."
  • Website: https://www.cloudhypervisor.org
  • Source code: https://github.com/cloud-hypervisor/cloud-hypervisor

Used in clouds:

• AWS:
  • Xen
  • Nitro Hypervisor: a modified KVM. For new kinds of EC2 instances.
• Google:
  • GCE: KVM
  • Cloud Run: gVisor
• Azure: Windows Hyper-V
• VMware: ESXi
• Oracle VM: Xen
• Redhat: Red Hat Virtualization (RHV), based on KVM.

Live Migration

KVM has included LM (Live Migration) for over a decade.

KubeVirt has been supporting Live Migration functionality out of the box since CY2020 (see https://kubevirt.io/2020/Live-migration.html)

Azure: https://docs.microsoft.com/en-us/azure/virtual-machines/maintenance-and-updates

Paravirtualization(PV) vs Hardware Virtual Machine (HVM)

• Paravirtualization: guest OS knows that it is running on a hypervisor instead of base hardware, recognizes that other virtual machines are running on the same machine
• Hardware Virtual Machine (HVM): guest OS thinks that it is running directly on the hardware

Xen supports 2 virtualization types; Amazon supports 2 types as it runs on Xen.

PV

• An OS or Kernel called Hypervisor is installed on the hardware.
• Dom0 is called the "privileged domain" which can issue commands to the hypervisor.

Pros

• Stability/Performance is close to the real servers and hardware virtualization.
• Overhead is very low.

Cons

• Implementation is tough.
• Both the host & guest kernels has to be patched.
• Supports Linux only.
• can’t change the OS options during install.
• Can’t compile and install a custom kernel.

HVM

• Stands for Hardware-assisted virtual machine.
• Provides complete hardware isolation. The hardware provides support to run independently for each OS.

Pros

• Can run Linux and Windows.
• Complete secure hardware isolation.
• Resembles close to a physical server.
• Greater stability.

Cons

• Low performance, because of the overheads at the hardware level.

Cloud Init

https://cloud-init.io/

cloud-init is a widely adopted project used for early initialization of a VM. Used by cloud providers such as AWS and GCP, cloud-init has established itself as the defacto method of providing startup scripts to VMs. It can also be used for generating and setting up SSH private keys

Software Defined Data Center (SDDC)

Redfish: specs for APIs.

E.g. Netapp ONTAP: Compute nodes are all RedFish API-compatible.