  Cloud computing is gaining more and more traction as a deployment and
provisioning model for software. While a large body of research already covers
how to optimally operate a cloud system, we still lack insights into how
professional software engineers actually use clouds, and how the cloud impacts
development practices. This paper reports on the first systematic study on how
software developers build applications in the cloud. We conducted a
mixed-method study, consisting of qualitative interviews of 25 professional
developers and a quantitative survey with 294 responses. Our results show that
adopting the cloud has a profound impact throughout the software development
process, as well as on how developers utilize tools and data in their daily
work. Among other things, we found that (1) developers need better means to
anticipate runtime problems and rigorously define metrics for improved fault
localization and (2) the cloud offers an abundance of operational data,
however, developers still often rely on their experience and intuition rather
than utilizing metrics. From our findings, we extracted a set of guidelines for
cloud development and identified challenges for researchers and tool vendors.
