With an estimated 20 billion connected devices by 2020 generating enormous amounts of data, more data-centric ways of working are needed to cope with the dynamic load and reconfigurability of on-demand computing. There is a growing range of complex, specialised means by which this flexibility can be achieved, e.g. Software-defined networking (SDN). Specification of Quality of Service (QoS) constraints for time-critical characteristics, such as network availability and bandwidth, will be needed, in the same way that compute requirements can be specified in today's infrastructures. This is the motivation for SWITCH -- an EU-funded H2020 project addressing the entire lifecycle of time-critical, self-adaptive cloud applications by developing new middleware and tools for interactive specification of such applications. This paper presents a user-facing perspective on SWITCH by discussing the SWITCH Interactive Development Environment (SIDE) Workbench. SIDE provides a programmable and dynamic graphical modeling environment for cloud applications that ensures efficient use of compute and network resources while satisfying time-critical QoS requirements. SIDE enables a user to specify the software components, properties and requirements, QoS parameters, machine requirements and their composition into a fully operational, multi-tier cloud application. In order to enable SIDE to represent the software and infrastructure constraints and to communicate them to other SWITCH components, we have defined a co-programming model using TOSCA that is capable of representing the application's state during the entire lifecycle of the application. We show how the SIDE Web GUI, along with TOSCA and the other subsystems, can support three use cases and provide a walk-through of one of these use cases to illustrate the power of such an approach
