Virtualization

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

Solutions

• VMware: losing popularity, especially after its acquisition by Broadcom (price hike, licensing change, etc).
• Microsoft Hyper-V: integrated into Windows Server.
• Nutanix AHV:A hypervisor integrated into the Nutanix hyperconverged infrastructure platform.
• Red Hat Virtualization (RHV): An open-source platform based on KVM, providing enterprise-grade features and support.
• Proxmox VE: An open-source hypervisor combining KVM and LXC containerization.
• Oracle VM VirtualBox: A popular desktop virtualization solution known for its ease of use and cross-platform support.
• Citrix Hypervisor: An enterprise-level hypervisor

Software Defined Data Center (SDDC)

Redfish: specs for APIs.

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