Live Migration of Virtual Machines Presented by: Edward Armstrong University of Guelph.

Live Migration of Virtual Machines

Presented by:Edward ArmstrongUniversity of Guelph

OverviewProblem DescriptionSolutionsStrengths and WeaknessesResults

Migrating an OS - Complexity

•Same machine.

•Hibernating a laptop.

Trivial

•Same Hardware, different Machine.

•Changing cluster nodes.

Moderate

•Different hardware.

Complex

Migrating an OS – Timescale

•Requires only long term storage to be migrated.

•Loses all process state information.

•Driver reloading solves hardware problems.

Reboot•Typically

performed on the same machine.

•Requires long term storage.

•Loses external connection information, ie. network status.

Hibernation

•Hibernation in short term storage (RAM).

•Typically used to maintain a low power state.

Suspend

•Processes are not implicitly frozen.

•Differences in hardware create problems.

•Solved by using virtual machines.

Live

ConsiderationsBoth machines must be active at

the same time.Migration of active live services.Total migration time.Resource contention.

Migrating memory

Push

PausePull

Memory - Pure stop and copy.

Pros◦ Simplicity.◦ Consistency.

Cons◦ Downtime proportional to

memory.◦ Unacceptable for live services.

Push

PausePull

Source Machine Target Machine

Memory - On demand migration.

Pros◦ Shorter downtime.◦ Consistency.

Cons◦ Longer migration time.

Push

PausePull

Target MachineSource Machine

Page fault request

Send page

Memory - Pre copy migration.

Pros◦ Copy low fault pages quickly.◦ Works well for live processes.

Cons◦ Large number of faults for

busy memory.

Push

PausePull

Target MachineSource Machine

Live page fault

Iterative push

Network and disk resources.Unique to an OS instance.Ordering of resources are non-

determinsitic.Need to maintain open network

connections.

Resolving network connections with an ARP* response.

Source MachineNo Address

Target Machine192.168.0.102

LAN

*ARP: Address Resolution Protocol

Packets

Resolving network connections with an ARP* response.

Source MachineNo Address

Target Machine192.168.0.102

LAN

*ARP: Address Resolution Protocol

Unsolicited ARP reply

Packets

Resolving network connections with an ARP* response.

Source Machine192.168.0.102

Target MachineNo Address

LAN

*ARP: Address Resolution Protocol

Packets

Network resources.Pros

◦Handled by external devices.◦Similar scheme can be used to

migrate disk services (not covered in paper).

Cons◦Small amount of packet loss.◦Requires a LAN with unsolicited ARP

responses enabled.

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source Machine Target Machine

Select a new target machine

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source Machine Target Machine

Confirm available resources on target.Failure means VM continues to run on source.

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source Machine Target Machine

Transfer memory.Retransmit memory used during transfer.

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source Machine Target Machine

Halt source to redirect network trafficand transfer CPU state.

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source Machine Target Machine

Verify transfer complete.Disable source.

Design Overview

Pre-Migration

Reservation Pre-Copy

Stop and CopyCommitActivate

Source MachineTarget Machine

Activate target machine

Summary of DesignAt all times there is at least one

consistent image available.Minimized down time.Not a fast process overall.Requires tuning.Requires certain hardware.

Performance – Dirty Pages.

8 second granularity, used to decide which pages make for good pre-migration.

Performance

Performance

1- 4 pre-copy iterations

Performance

1- 4 pre-copy iterations

Performance

1- 4 pre-copy iterations

Thank You