Scheduling Physical Machine Maintenance on Qualified Clouds: What if Migration is not Allowed?

Increasingly, cloud systems host IT services for critical domains such as public health and electric power. Such cloud systems need to be qualified and validated in accordance with compliance policies or government regulations. Configurations of such qualified cloud systems, including VM placement and software deployment, are limited to a small set of configurations which passed the qualification and validation process. So, on practical qualified cloud systems, on-demand VM migration or replication is not allowed. We address the problem of optimally scheduling physical machine maintenance on qualified cloud systems where VM placement cannot change dynamically. Particularly, we try to minimize the number of maintenance waves, and hence, minimize the qualified cloud systems' exposure to loss of high availability. Moreover, we study how the initial placement of service component replicas can help optimize the maintenance schedule while minimize the hardware cost, which is much higher on qualified cloud systems than regular ones. Evaluations in simulations and our real-world qualified cloud system demonstrate the effectiveness of our algorithms and justify our algorithm selection in the real qualified system. In particular, our approach eliminated impacts on service workload and availability during maintenance, while simultaneously largely reduced maintenance time.