  The cloud computing paradigm offers on-demand services over the Internet and
supports a wide variety of applications. With the recent growth of Internet of
Things (IoT) based applications the usage of cloud services is increasing
exponentially. The next generation of cloud computing must be energy-efficient
and sustainable to fulfil the end-user requirements which are changing
dynamically. Presently, cloud providers are facing challenges to ensure the
energy efficiency and sustainability of their services. The usage of large
number of cloud datacenters increases cost as well as carbon footprints, which
further effects the sustainability of cloud services. In this paper, we propose
a comprehensive taxonomy of sustainable cloud computing. The taxonomy is used
to investigate the existing techniques for sustainability that need careful
attention and investigation as proposed by several academic and industry
groups. Further, the current research on sustainable cloud computing is
organized into several categories: application design, sustainability metrics,
capacity planning, energy management, virtualization, thermal-aware scheduling,
cooling management, renewable energy and waste heat utilization. The existing
techniques have been compared and categorized based on the common
characteristics and properties. A conceptual model for sustainable cloud
computing has been proposed along with discussion on future research
directions.
