Linux Virtualization

A General Overview

Austin Godber

godber@uberhip.com

http://uberhip.com/godber/

Motivations for Virtualization

Server Consolidation - power savings, increased hardware utilization
Disaster Recovery - live standby
Deployment Staging - test patches, upgrades, experimentation
Application Portability - live migration, resource scaling
Application Isolation - accomodate orthogonal requirements, some security benefits
Nifty Features - Suspend/Resume, Snapshots

Types of Virtualization

Hardware Emulation

Supports Disparate CPU Architectures
Emulation at the CPU Instruction Level
Tends to be slow
Example Implementations: QEMU, Bochs, MAME

OS/API Emulation

Allows execution of a guest application on the host OS.
Reimplementation of the guest's system and library interfaces on the Host platform
Faster than emulation without the overhead of running the entire guest OS.
Example Implementations: Wine, LxRun
Lx Brand Example

Types of Virtualization

Full/Native Virtualization

Guests must have same CPU Architecture as host.
Host emulates hardware devices that Guest must support.
Gets tricky without hardware support, because it must dynamically scan executing code for trouble.
Example Implementations: VMWare Player, GSX, and ESX, Parallels Workstation, VirtualBox

Paravirtualization

Requires Guest OS Modification which avoids the runtime scanning of guest code.
Guest Applications do not need modification.
Example Implementations: Xen, Lguest

Types of Virtualization

Hardware Assisted Full Virtualization

Guests must have same CPU Architecture as host.
Hardware support must be present: Intel VT or AMD SVM extensions
Example Implementations: Xen HVM

OS Level Virtualization

Requires host kernel modifications.
Example Implementations: OpenVZ, Linux-VServer, FreeVPS

Pitfalls of Virtualization

Increased Complexity

Networking - More tubes!

Suspend/Resume Issues

Increased Magnitude of Fat Finger Catastrophe
Security Questions - Just coming up, BluePill, Information Leakage (CPU and Network)

Linux DIY Options

Most distributions released since late 2006 have supported some form of virtualization. Intially the support was for Xen and has recently begun changing to KVM.

Using Ubuntu 7.04 as the baseline, what can we get?

KVM is easy ... modprobe
Xen is not too bad (reboot required)
VMWare Player and VMWare Server GSX are availble from commercial repos

Virtualization Miscellenia

Virtual Appliances - Preconfigured Applications
Management Tools - Management tools, Enomolism, Google's Ganeti
Development Tools - libvirt, commercial tools (VMWare)
Integrated into Hardware - All of this will soon disappear under the covers.

KVM on Ubuntu 7.04

These instructions are consolidated from the Ubuntu Wiki KVM HOWTO.

Check to see if you have the hardware extentions:
```
grep vmx /proc/cpuinfo
```
Insert Module:
```
sudo modprobe kvm-intel
```
Create Disk Image:
```
qemu-img create edgy.img -f qcow 6G
```

Boot up off Install Disk:

sudo kvm -m 256 -cdrom ~/ubuntu-6.06-server-i386.iso -boot d edgy.img

Easy right? It doesn't work, but it will probably be this easy soon.

KVM on Ubuntu 7.04 - fixed

Make a bridge (/etc/network/interfaces):

auto lo eth0 br0

iface lo inet loopback

iface br0 inet dhcp
        bridge_ports eth0
        bridge_maxwait 2
        up /sbin/ifconfig eth0 inet 0.0.0.0 promisc
        
iface eth0 inet static
        address 172.16.5.0
        netmask 255.255.255.0

Restart networking:
```
sudo /etc/init.d/networking restart
```

KVM on Ubuntu 7.04 - fixed

Boot with the appropriate networking hints:

sudo kvm -m 256 -net nic -net tap \
     -cdrom ~/mini.iso -boot d edgy.img

Yes, I am cheating by starting it with sudo.
This will be effortless in no time. Not that it was terribly hard. The bridge is a bit of a nuisance however.

Hosting

There are all types of virtual hosting today. It started out with UML or jail type hosting and gradually progressed through all the virtualization technologies. Today you can find very sophisticated cluster based hosting providers. Particularly interesting is 3tera and Amazon's EC2 for their dynamic provisioning and flexibility. RailsMachine is noteworthy for it's utilization of Xen to solve the Rails deployment problem.