A Taxonomy of SDN-enabled Cloud Computing

ing with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. © 2017 Association for Computing Machinery. 0360-0300/2017/3-ART1 $15.00 https://doi.org/0000001.0000001 ACM Computing Surveys, Vol. 1, No. 1, Article 1. Publication date: March 2017. 1:2 J. Son and R. Buyya of switches connecting tens of thousands of servers. Each server can serve multiple application requests from different users by using virtualization technologies, which have been enhanced vastly in processing and storage resources for the last couple of decades but not in network resources. Currently, cloud customers can rent virtualized computing resources, i.e., virtual machines (VMs), and virtualized storages from providers which are allocated virtually for the customer. However, the network resource virtualization technology is still far from being utilized in the commercial public clouds. Servers are allocated to multiple tenants if the total requested size is not exceeding the server capacity. Thus, cloud customers are capable of requesting a smaller sized resource than the capacity of the entire server, and a server can provide multiple VMs [33]. These VMs communicate to each other and the Internet through a number of network switches and routers. Data center network (DCN) is established and managed in order to transfer the traffic between VMs efficiently. As DCN connects tens of thousands of servers, the network will have a high complexity which makes it difficult to manage and scale in the traditional networking paradigm. In traditional networks, each network switch has its own control logic which individually decides its behavior based on the information obtained from its neighbors. The traditional network approach is inefficient when it comes to the cloud data center where a higher density of servers provides multiple VMs which dynamically transforming from time to time. To overcome the shortcomings of traditional networks, cloud data centers started adopting software-defined networking (SDN) concept in their DCN. SDN provides a centralized control logic with a global view of the entire network at the central controller and dynamically change the behavior of the network. It can also adjust the network flow dynamically by the controller which is well fitted for the dynamic nature of the cloud service. Giant cloud providers such as Google already adopted SDN concept in their data center to increase the scalability and manageability [81]. Although many surveys and taxonomies have been presented in cloud computing and SDN contexts, each of them has been addressed a specific problem in the area. For example, Toosi et al. [80] presented a survey focusing on inter-connected cloud computing. The paper includes interoperability scenarios with multiple data centers and detailed explanation of various approaches to operate and use inter-connected cloud data centers. The article described networking challenges for inter-clouds in a sub-section, but the primary focus was on the wider issues for integrating multiple cloud data centers as a cloud broker’s perspective. Mastelic et al. [53] also presented a survey in energy efficiency for cloud computing. A systematic category of the energy consumption in cloud computing has been suggested in the context of hardware and software infrastructure in clouds. The authors also included a networking aspect emphasizing on DCN, inter-data center network, and end-user network. A comprehensive survey has been presented in various aspects of energy efficiency including networks, however the paper is in lack of SDN context. Jararweh et al. [41] provided details of Software-defined clouds focusing on systems, security, storage, and networking, but with more focus on the system architecture rather than the individual research works in SDN-clouds. In this paper, both SDN and cloud computing are considered as the survey topic. Among the enormous studies conducted in both distributed computing and networking disciplines for cloud computing and SDN respectively, we select the state-of-the-art considering both aspects simultaneously. Although several surveys have been presented in each context separately, this paper is the first attempt to the best of our knowledge that explores the research considering both aspects at the same time. We emphasize on SDN utilization and challenges in the context of cloud computing. The rest of the paper is organized as follows: in Section 2 we present an overall background of cloud computing, DCN, and SDN. Section 3 provides the description and definition of SDN-enabled cloud computing, followed by a taxonomy of the usage of SDN in cloud computing in various aspects ACM Computing Surveys, Vol. 1, No. 1, Article 1. Publication date: March 2017. A Taxonomy of SDN-enabled Cloud Computing 1:3 (Section 4). In Section 5, comprehensive surveys have been undertaken to find the achievement and the challenges in SDN usage in clouds in the context of energy efficiency, performance, virtualization, and security enhancement. The following section presents a survey of simulation and empirical methods developed for evaluation of SDN-enabled cloud computing (Section 6). We investigate the shortcomings of the current research and propose the future directions in Section 7, and finally, summarize and conclude the paper.