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

Overview Problem Description Solutions Strengths and Weaknesses Results

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

Considerations Both 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 MachineTarget 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 Machine No Address Target Machine LAN *ARP: Address Resolution Protocol Packets

Resolving network connections with an ARP* response. Source Machine No Address Target Machine LAN *ARP: Address Resolution Protocol Unsolicited ARP reply Packets

Resolving network connections with an ARP* response. Source Machine Target Machine No 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 ReservationPre-Copy Stop and Copy CommitActivate Source MachineTarget Machine Select a new target machine

Design Overview Pre- Migration ReservationPre-Copy Stop and Copy CommitActivate Source MachineTarget Machine Confirm available resources on target. Failure means VM continues to run on source.

Design Overview Pre- Migration ReservationPre-Copy Stop and Copy CommitActivate Source MachineTarget Machine Transfer memory. Retransmit memory used during transfer.

Design Overview Pre- Migration ReservationPre-Copy Stop and Copy CommitActivate Source MachineTarget Machine Halt source to redirect network traffic and transfer CPU state.

Design Overview Pre- Migration ReservationPre-Copy Stop and Copy CommitActivate Source MachineTarget Machine Verify transfer complete. Disable source.

Design Overview Pre- Migration ReservationPre-Copy Stop and Copy CommitActivate Source Machine Target Machine Activate target machine

Summary of Design At 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

Performance