Virtualization

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Virtualization

• Xen , Linux Vserver , Planet Lab

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Paper

• Container-based Operating System Virtualization
  A Scalable, High-performance Alternative to Hyper
  visors Stephen Soltesz, Herbert Potzl, Marc E.
  Fiuczynski, Andy Bavier, and Larry Peterson
• Princeton University
• PlanetLab Architecture An Overview Larry
  Peterson, Steve Muir, Timothy Roscoey, Aaron
  Klingaman
• Princeton University , Intel Research
  Berkeley

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What is virtualization ?

• Virtualization is a broad term which refers to
  many different aspects of computing. In essence
  has to be some sort of abstraction of resources.
• These resources could be computing power or
  storage.

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Why is virtualization important ?

• The one server one application idea can be
  avoided. Multiple servers can coexist on the same
  physical machine bringing IT costs down. Also
  makes administration easier.

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Why is virtualization important ?

• Data Recovery
• Other areas include research areas such as Planet
  Lab , High Performance Clustering etc.
• http//news.zdnet.com/2036-2_22-6058678.html

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Basic Concepts

• Host The physical computer on which the virtual
  machine is loaded.
• Virtual Machine Its a software environment
  which appears to a guest OS as hardware. It
  consists of some computing power (CPU), Memory,
  NIC, and hard drive.
• Virtualization Layer This is what is available
  as resources to the virtual machines. Also know
  as virtual machine monitor.

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Different Virtualization Models

• Vmware Model
• Xen Model
• Linux Vserver Model

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VMware model

• Reference Virtualization with VMware ESX Server
  By Al Muller, Seburn Wilson
• Publisher Syngress

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Full Virtualization

• It provides total abstraction of the underlying
  physical system and creates a complete virtual
  system in which the guest operating system can
  execute.
• No modification is required in the guest OS or
  application.
• Example VMware ESX server

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Drawbacks of Full Virtualization

• X86 architecture is not meant for virtualization.
  This reduces performance and increases
  complexity.

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Xen Model

• Reference http//www.dell.com/downloads/global/p
  ower/ps3q05-20050191-Abels.pdf

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Para virtualization

• This provides each VM with an abstraction of the
  hardware that is similar but not identical to the
  hardware.
• It requires modification to the guest OS that are
  run on the VM.
• No changes to the ABI are to be made, so
  applications remain the same.

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Issues in Virtualization

• Efficiency Vs Isolation
• The paper argues that isolation is dependant on
  the usage scenario. It sacrifices isolation
  partially in favour of performance.

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Motivation for Container based OS

• Organizations run many copies of the same server
  software, operating system distribution and
  kernels in their mix of VMs.
• If this is the case then the same shared
  virtualized OS image can be used for all virtual
  machines.

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Container Based OS VMM
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Container Based OS VMM

• Hosting platform consists of the shared OS image
  and the privileged host (VMHost).
• VMHost This is the VM that the system admin
  uses to manage other VMs.

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How does this differ from Xen ?

• Fault Isolation Container based VMM cant
  provide fault isolation as they use a single
  shared kernel. So if the kernel fails, all the
  VMs are affected.
• Resource Isolation VMM should be able to
  isolate one VM from accessing resources of
  another VM.
• Security Isolation VMM should isolate access to
  logical objects such as files, memory addresses,
  user ids and so on.

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How does this differ from Xen ?

• Key Difference Hypervisors can run multiple
  kernels while container based OS VMM cant do
  that.
• On the other hypervisor based systems cant have
  live update.

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Security Isolation in container based VMM

• Contexts Separation of namespaces
• Filters Access Control Lists
• Hardware virtualization

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Resource Isolation

• CPU Isolation
• Token bucket filter runs on top of O(1)
  scheduler.
• Each VM has a bucket where it collects tokens at
  a specified rate.
• Tokens are charged on the basis of running
  processes per VM.

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Resource Isolation

• Network Isolation
• Hierarchical Token bucket is used to provide
  bandwidth reservations.
• Each VM has a specified reservation and a share.
• Each packet has a context id tagged to it to map
  it to the VM.

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Security Isolation

• Processes belonging to different VMs are not
  allowed to interact with each other.

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Comparison
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Planet Lab Overview

• Planet Lab is a geographically distributed
  platform for deploying, evaluating, and accessing
  planetary-scale net-work services.
• The internet has been a success and as a result
  has become ossified that is it is resistant to
  change. Its difficult to introduce new ideas
  without trying them out.
• Reference http//www.planet-lab.org
  /Talks/2004-01-30-APAN.pdf
• Planet Lab is a sort of a test bed or deployment
  platform of 1000 servers spread across more than
  35 countries.

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Planet Lab Features

• Distributed Virtualization The need is for a
  global platform that supports broad coverage
  services at multiple points of presence.
• Each service runs as a slice of Planet Labs
  global resources.
• What is a slice ?
• A slice is a network of virtual machines.

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Planet Lab Features

• Node A physical machine capable of one or more
  virtual machines. It must have at least one
  non-shared IP address. Each unique node has a
  unique node Id.

Node Mgr
Local Admin
VM1
VM2
VMn

Virtual Machine Monitor (VMM)
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Planet lab Features

• Node Manager It is a program running on each
  node that creates VMs on that node and controls
  the allocation of resources to those VMs.

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Slices
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Slices
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Slices

• The individual VMs that make up a slice contain
  no information about the other VMs in the set.
• The slice state is maintained by the Slice
  Authority. This task is done by the PLC for
  system wide slices.
• Creating a slice is a multistage process
  involving the node owner, slice creation service
  and a slice authority.