VMFT - Primary-backup replication

Overview

• system layers
  • Physical machine, OS/hypervisor, VM, OS/VM, Systems App, App
• replication in different layers
  • e.g., replicating GFS master
• virtual machine basics
  • a stream of instruction logs
  • inputs / outputs

Approaches

• pause, replicate states, continue (migration)
  • easy to implement
  • but cost time, can be used in adding new replica
• state machine, replicate inputs
  • efficient in performance

Correctness

• Input events need to be replicated at exact point of instruction
• When can primary return?
  • ack from F followers: tolerate F failures
  • otherwise?

Non-determinism

• clock
  • record
• multi-core (different from multi-thread)
  • not supported in vmft
• IO race
  • non-blocking
  • DMA

Input/Output consistency

• exactly once over network? (TCP, UDP)
• disk read

Network partition and “split-brain”

• perfect failure detector? no
• atomic test and set
• can lease solve the problem?