Cloud computing has been recognized as the de facto computing utility standard for hosting and delivering services over the Internet. Cloud platforms are being rapidly adopted by business owners and end-users thanks to its many superiorities to traditional computing models such as cost saving, scalability, unlimited storage, anytime anywhere access, better security, and high fault-tolerance capability. However, despite the fact that clouds offer huge opportunities and services to the ICT industry, the landscape of cloud computing research is being expanded due to several reasons, such as emerging data-intensive applications, multicloud deployment models, and more strict non-functional requirements on cloud-based services. In this paper, we study a comprehensive taxonomy of main cloud computing research areas, discuss state-of-the-art approaches for each area and the associated sub-areas, and highlight the challenges and future directions per research area. The survey framework, presented in this paper, provides useful insights and outlook for the cloud computing research and development, allows broader understanding of the design challenges of cloud computing, and sheds light on the future of this fast-growing computing paradigm.