0 DAHM : A Green and Dynamic Web Application Hosting

Dynamic Application Hosting Management (DAHM) is proposed for geographically distributed data centers, which decides on the number of active servers and on the workload share of each data center. DAHM achieves cost-efficient application hosting by taking into account: (i) the spatio-temporal variation of energy cost, (ii) the data center computing and cooling energy efficiency, (iii) the live migration cost, and (iv) any SLA violations due to migration overhead or network delay. DAHM is modeled as fixed-charge min-cost flow and mixed integer programming for stateless and stateful applications, respectively, and it is shown to be NP-hard. We also develop heuristic algorithms and prove, when applications are stateless and server have identical power consumption model, that the approximation ratio on the minimum total cost is bounded by the number of data centers. Further, the heuristics are evaluated in a simulation study using realistic parameter data; compared to a performance-oriented application assignment, i.e., hosting at the data center with the least delay, the potential cost savings of DAHM reaches 33%. The savings come from reducing the total number of active servers as well as leveraging the cost efficiency of data centers. Through the simulation study, the paper further explores how relaxing the delay requirement for a small fraction of users can increase the cost savings of DAHM.