Trustable virtual machine scheduling in a cloud

Abstract

In an Infrastructure As A Service (IaaS) cloud, the scheduler deploys VMs to servers according to service level objectives (SLOs). Clients and service providers must both trust the infrastructure. In particular they must be sure that the VM scheduler takes decisions that are consistent with its advertised behaviour. The difficulties to master every theoretical and practical aspects of a VM scheduler implementation leads however to faulty behaviours that break SLOs and reduce the provider revenues. We present SafePlace, a specification and testing framework that exhibits inconsistencies in VM schedulers. SafePlace mixes a DSL to formalise scheduling decisions with fuzz testing to generate a large spectrum of test cases and automatically report implementation faults. We evaluate SafePlace on the VM scheduler BtrPlace. Without any code modification, SafePlace allows to write test campaigns that are 3.83 times smaller than BtrPlace unit tests. SafePlace performs 200 tests per second, exhibited new non-trivial bugs, and outperforms the BtrPlace runtime assertion system.