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Migration ofComputing Environments
분산시스템연구실
김은성
2006-11-06
SNU DCSLabhttp://dcslab.snu.ac.kr
Contents
IntroductionVirtual ComputerInternet Suspend/Resume (ISR)The Stanford Collective ProjectMigration of Virtual machines in VmotionMobiDesk: Mobile Virtual Desktop
Computing
SNU DCSLabhttp://dcslab.snu.ac.kr
Introduction
Multiple work-site environment Required identical work environment
In the 1960s, mainframe servers Simple, “dumb” terminals Central data storage
Portable devices such as laptop computers Two significant disadvantages
• The user is required to carry a physical device to transport the environment.
• The user is responsible for the physical security of the portable device at all times.
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Introduction
Migration of computing environments Capsule: the state of a machine
• The state of the resources used by the OS and the applications
• The code and data belonging to the OS and applications
This requires• All this state information to be encapsulated,• Transmitted across a network, and• Installed on the other computer before the user
can take over operation at a second computer.
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Virtual Computers
VM migration-based computing environment Virtual machine technology
• Provides the ability to capture the entire state of a computer system.
• Facilitates migration of a full computing environment.
Virtual machine itself can server as a capsule.
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Virtual Computers
Several issues The time taken to migrate the entire state of a
computer• Not necessary to send the entire state from one computer to
another initially• Information already available on the second computer
Compression and encryption• To reduce the amount of data transmitted• To transmit it securely
Different hardware architecture Performance
• The different ISA between the user’s VM and the host computers
• Binary translation and optimization techniques
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Internet Suspend/Resume (ISR)
Assumption A user suspends operation on
one machine, travels to another machine, and resumes execution on the other machine.
VMware GSX Server Migration using a distributed file s
ystem VMM keeps a capsule in a file
on a distributed file system. 2.5-30 seconds from distributed fi
le system at LAN speeds
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Internet Suspend/Resume (ISR)
Several problems The need to change the IP address to access the network and al
l references to this address in the saved environment• MobileIP technology
Long migration time• The organization of the state information in modules that are loaded
incrementally “Pull” model: long latency
• Destination computer reading in the environment state file on demand
• Proactively copying in the state to the local machine even before the user requests it
Only the changes to the environment need be loaded. Reusing the environment of other users already on the system
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MobileIP Network
Mobile End-systemInternet
Router
Router
Router
End-system
FA
HA
MN
Home Network
Foreign Network
(Physical home network for the MN)
(Current physical network for the MN)
CN
SNU DCSLabhttp://dcslab.snu.ac.kr
MobileIP in Action
Internet
Sender
FA
HA
MN
Home Network
ForeignNetwork
Receiver
1
2
3
1. Sender sends to the IP address of MN, HA intercepts packet (proxy ARP)2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN
CN
SNU DCSLabhttp://dcslab.snu.ac.kr
MobileIP in Action
Internet
Receiver
FA
HA
MN
Home Network
ForeignNetwork
Sender
1
1. Sender sends to the IP address of the receiver as usual, FA works as default router
CN
SNU DCSLabhttp://dcslab.snu.ac.kr
The Stanford Collective Project
“Push” model A capsule is sent to the destination computer
directly. The user can have instantaneous access to hi
s or her environment at the destination site.VMware GSX ServerTunneling of network packets over a VPN20 minutes at DSL speeds
SNU DCSLabhttp://dcslab.snu.ac.kr
The Stanford Collective Project
Reducing memory state before migration Balloon program
• Requests a large number of pages on a virtual machine.• Expectation is that these pages are released from the
currently inactive processes that do not need to respond instantaneously on a resume at the destination.
• The size of the memory state which is transferred is now reduced.
Several subtle policy issues• Reduction of memory size vs. overhead of resume operation• Active pages that are easily compressible
SNU DCSLabhttp://dcslab.snu.ac.kr
The Stanford Collective Project
Reducing the size of the transmitted packet The state represented by the disk is rather formidable. By maintaining differences between capsules rather
than the full disk image for each capsule Capsule hierarchy
• Incremental disk with the copy-on-write concept– Many different versions to share a single copy of the actual
data
– Particularly effective when these versions are largely the same and differ in only some small aspects.
• When the student moves to another computer, the currently open incremental disk image is transferred to the new computer.
SNU DCSLabhttp://dcslab.snu.ac.kr
The Stanford Collective Project
UniversityCapsule
Department1Capsule
Department12Capsule
Student1Capsule
Student2Capsule
Student3Capsule
Department2Updated Capsule
Student4Capsule
Root node: the state of the disk
is saved in its entirety
Child node: Save the incremental
states of the parent andthe child
The state of the disk at any nodecan be derived from the disk infocontained in the nodes along the
path from the root.
Student1 WorkingCapsule
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The Stanford Collective Project
Reducing start-up time on a resume On demand fetch for the information in the ca
psule, rather than being prefetched completely
• All accesses to disks are intercepted by the VMM and forwarded to a disk server.
• The disk server translates the request to an access in one of the nodes in the hierarchy.
• Local shadow copies
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The Stanford Collective Project
Reducing transmission time and bandwidth by exploiting redundancy in disk blocks Hashed copy scheme
• Instead of transferring the actual data blocks, transmits the computed hash values of the data blocks.
• When a disk block is needed, checks to see whether a block with the same hash value is available locally.
• If the block is not available locally, the computer broadcasts a request for a copy.
SNU DCSLabhttp://dcslab.snu.ac.kr
The Stanford Collective Project
Results of experiments
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Migration of Virtual machines in VMotion
VirtualCenter Infrastructure management software that manages a cluster of In
tel IA-32 virtual machine systems connected in a local-area network
Deployment and monitoring of virtual machine
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Migration of Virtual machines in VMotion
VMotion Part of the VirtualCenter for migration Characteristics
• Load balancing – To improve the response time of the system through better utilization of
resources
• Security – To quarantine a virtual machine that has been attacked
• Collocation– To bring communicating virtual machines close together
• Fault tolerance– To move a failing host to another processor
• Power management– To move the load away from an overheated processor
• Maintenance– To move the load away from some processor while it is upgraded
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Migration of Virtual machines in VMotion
Restriction of VMotion The source and destination computers must be in the
same server cluster managed by the same VirtualCenter manager.
The file systems on the source and destination computers must be identical and located on shared disks in a SAN.
The processors must have the same architecture and be provided by the same vendor.
The virtual machine supports a Gigabit Ethernet adapter.
The virtual machines should be running only stand-alone applications.
SNU DCSLabhttp://dcslab.snu.ac.kr
Migration of Virtual machines in VMotion
VMotion actions It first ensures that the virtual machine is in a
stable state on the current host. It then copies the contents of the memory bel
onging to the virtual machine to the destination host. (baseline copy)
The virtual machine on the original host is suspended. (incremental capsule)
It then activates the virtual machine on the new host.
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MobiDesk: Mobile Virtual Desktop Computing
A mobile virtual desktop computing hosting infrastructure Similar with the Windows Remote Desktop Connection
Features Users can move across different end-devices while
keeping their computing sessions. Computing sessions can be migrated from one hosting
server to another. Low overhead
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MobiDesk: Mobile Virtual Desktop Computing
Moving across end-devices Users interact with MobiDesk sessions
through session viewer. Upon 1st login, authentication is performed
and the session view is connected to a session server through a proxy.
When the user disconnects, the sessions continues to run on the session server.
On next connection, the session will be in the same state it was when the user last disconnected.
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MobiDesk: Mobile Virtual Desktop Computing
Migration across servers Sessions can be checkpointed and migrated t
ransparently at any point in time. This feature is useful when the hosting server
needs to be updated.
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MobiDesk: Mobile Virtual Desktop Computing
How MobiDesk accomplish this For client migration – decouples a user’s
computing session from the display.• By moving all application logic to hosting providers
(session servers)
For session migration – decouples the computing session from the underlying OS and the network resources.
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
MobiDesk architecture
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
Display virtualization Designed as a virtual video device driver
• Wrap the display commands from session applications,
• And send them to a remote client over the network.
Session server keeps the state of the virtual display.
Deploys a server-push model for sending display updates to the client.
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
Operating system virtualization Provide a unique name-space for each
session.• OS resources are now identified with virtual
identifiers.
In each name-space, a traditional environment is provided to the application.
Sessions• Virtualization• Migration
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
Operating system virtualization Session virtualization
• The virtualization layer associates a virtual name to an appropriate OS physical name.
• System call interposition– Wrappers around system calls that translate virtual name
s to physical names and prevent accesses across the session boundary
• chroot utility and file system stacking– Provide each session with its own file system namespac
e
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MobiDesk: Mobile Virtual Desktop Computing
Operating system virtualization Session migration
• Using a checkpoint-restart mechanism• To avoid dependencies on low-level kernel details,
processes are required to be suspended before checkpoint.
• The new hosting server use a session cookie to notify the proxy.
• Limitation of session migration:– Migrate between machines with a common CPU
architecture– Kernel differences are limited to maintenance and
security patches.
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
Network virtualization Issues
• Multiple sessions on the same server may run the same service.
• Ongoing network connections must be preserved when a session is migrated from one server to another.
All servers on same subnet• Each session gets an IP address from the DHCP server and
uses it as an alias on the NIC on the attached server• Gratuitous ARP is used to resolve MAC address change
when sessions are migrated• Proxy re-directs traffic to and from aliased addresses
corresponding to individual sessions
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MobiDesk: Mobile Virtual Desktop Computing
Network virtualization All servers on different subnets
• Cannot migrate an aliased address obtained in one subnet to another (Inconsistency)
– Solution: use virtual addresses for proxy mapping and map these virtual addresses to physical (aliased) addresses dynamically at the proxy
• The aliased address may be reused in old subnet, confusing the proxy (Conflict)
– Solution: each session is bound to a different virtual NIC at the proxy, and labels in packets are used to identify the virtual NIC to which the session is bound
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MobiDesk: Mobile Virtual Desktop Computing
Network virtualization
SNU DCSLabhttp://dcslab.snu.ac.kr
MobiDesk: Mobile Virtual Desktop Computing
Benefits over current computing High-availability and reliable application
services Persistence and continuity of business logic Secure, low-cost global access and
transparent user mobility On-demand access to application and
computational resources Bridging the information gap
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Thank you
Any questions or comments?
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