Introduction to VM, libvirt, KVM

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Introduction to VM, libvirt, KVM

Robert Wang 2014/5/26

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What is a virtual machine

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Virtual Machine

• System VM

• provide a environment for executing an OS

• usually does hardware virtualization

• Process VM

• executing a single process

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Why do we need virtual machines

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Resource Sharing/Consolidation

• Example: Need to run web, mail, file, x, y, z, total of 10 servers. Do we need 10 physical servers?

• Put them into one server?

• How?

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Massive Deployment

• Example: Build 100 the web frontend servers.

• Install manually?

• Install via scripts?

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Isolation

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Run Legacy Software

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Software Development

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Snapshot

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System VMs

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Concept

Hardware Hypervisor

Guest OS Guest OS Guest OS

App App App App App App App App App

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Hypervisor

• also called virtual machine monitor (VMM)

• manage mappings

• disks, memory

• manage sharing

• cpus, network

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x86 Protection Ring: No Virtualization

Hardware Guest OS

App App App

Guest OS executes privileged instructions for App.

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x86 Protection Ring: With Virtualization

Hardware Guest OS

App App App

Hypervisor

Hypervisor executes privileged instructions for Guest OS.

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Types of Hypervisor

• Type 1: native (bare metal)

• need to implement its own drivers

• (eg. Xen, VMware ESX/ESXi)

• Type 2: hosted

• can reuse OSes’

implementations.

• (eg. VirtualBox, VMware Workstation)

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Types of Hardware Virtualization

• Full Virtualization

• Para-virtualization

• Hardware-assisted virtualization

!

• [NOTE: they are not disjoint.]

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Full Virtualization

• Complete simulation of hardware devices.

• Not quite possible on x86 until some hardware support.

• Binary translation.

• Slow!

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Para-virtualization

• Modified OS to avoid most trapping instructions.

• Custom I/O drivers.

• (eg. Virtio)

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Hardware-assisted Virtualization

• Aim to provide high performance full virtualization.

• Intel VT-x, AMD-V instruction set.

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Kernel Virtual Machine

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KVM

• Strictly speaking, KVM is a linux kernel module.

• Provides a set of APIs to accelerate virtualization.

• Utilizing Intel VT-x or AMD-V.

• I/O part is handled by QEMU.

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KVM

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Using KVM — Simple Way

• Create a virtual disk file

• qemu-img create -f qcow2 vdisk.img 10G

• Boot the machine (w/ install CD)

• kvm -hda vdisk.img -cdrom /path/to/boot-media.iso - boot d -m 512

• (“kvm” may be named “qemu-system-x86_64” on some distributions.)

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Using KVM — The complex way

• qemu-system-x86_64 -machine accel=kvm:tcg -name robertabcd -S - machine pc-q35-1.6,accel=kvm,usb=off -cpu host -m 1024 -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid

f68ef371-4cd6-2406-d5e0-41ad6210c22c -nographic -no-user-config - nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/

qemu/robertabcd.monitor,server,nowait -

monchardev=charmonitor,id=monitor,mode=control -rtc base=utc -no- shutdown -device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1 - device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x1 -

device piix3-usb-uhci,id=usb,bus=pci.2,addr=0x1.0x2 -drive file=/

dev/vmhost/robertabcd.img,if=none,id=drive-virtio-

disk0,format=raw -device virtio-blk-pci,scsi=off,bus=pci.

2,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 - netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=32 -device virtio- net-pci,netdev=hostnet0,id=net0,mac=52:54:00:b3:08:a8,bus=pci.

2,addr=0x3 -chardev pty,id=charserial0 -device isa-

serial,chardev=charserial0,id=serial0 -device virtio-balloon- pci,id=balloon0,bus=pci.2,addr=0x4

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libvirt

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What is “libvirt”?

• A toolkit to interact with virtualization softwares.

• A long term stable API.

• Supports a wide range of hypervisors:

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Setup VMs

• libvirt uses XML for definitions.

• You “define/undefine” a virtual machine.

• You “start/destroy” a domain (think a running virtual machine).

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“virtinst” Package

• virt-install  

--connect qemu:///system   -n "robertabcd"  

-r 1024  

--vcpus 2  

--accelerate  

--disk /dev/vg/disk,bus=virtio,format=raw   -w bridge=br0  

--nographics  

-x console=ttyS0   --location “…”

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Hate CLI?

• It has a GUI manager: “virt-manager”.

• Think twice before using GUI.

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Reference

• Getting Started (Debian/Ubuntu)

• https://help.ubuntu.com/12.04/serverguide/libvirt.html

• See libvirt documentation for tunable options and APIs

• http://libvirt.org/