###### Abstract  
Although there are e-health systems for the care of elderly people, the reactive characteristics to enhance scalability and extensibility, and the use of this type of system in smart cities, have been little explored. To date, some studies have presented healthcare systems for specific purposes without an explicit approach for the development of health services. Moreover, software engineering is hindered by agile management challenges regarding development and deployment processes of new applications. This paper presents an approach to develop health Internet of Things (IoT) reactive applications that can be widely used in smart cities for the care of elderly individuals. The proposed approach is based on the [PERSON]'s iterative architectural design process, the use of architectural patterns, and the Reactive Manifesto Principles. Furthermore, domain-driven design and the characteristics of the emerging fast data architecture are used to adapt the functionalities of services around the IoT, big data, and cloud computing paradigms. In addition, development and deployment processes are proposed as a set of tasks through DevOps techniques. The approach validation was carried out through the implementation of several e-health services, and various workload experiments were performed to measure scalability and performance in certain parts of the architecture. The system obtained is flexible, scalable, and capable of handling the data flow in near real time. Such features are useful for users who work collaboratively in the care of elderly people. With the accomplishment of these results, one can envision using this approach for building other e-health services. cloud computing; container as a service; DevOps; e-health; emerging fast data architecture; Internet of Things (IoT); reactive system +
Footnote †: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. of elderly people has been proposed (see Section 2), but does not exploit the benefits of using reactive properties to facilitate the implementation of architectures for distributed pervasive systems. To date, several studies have presented healthcare systems for specific purposes without a common or explicit approach for the development of health services. Other studies do not take advantage of the use of the cloud computing to develop services in scenarios such as a smart city. In addition, the solutions of these studies often have scalability, interoperability, and extensibility issues. On the other hand, software engineering has new challenges to address for the creation of innovative solutions based on new paradigms or technologies. Thus, some lines of research are related to the software process, software methodologies, design pattern development, privacy and security, and big data for software engineering [2]. Thus, software creation processes need appropriate strategies to manage the increasing complexity of the systems. One of the techniques used to deal with the design of applications is domain-driven design (DDD). DDD is used as a structured technique that helps manage the design of application complexities and establish delimited contexts to establish microservices. Currently, the use of the Internet of Things (IoT), which is a form of implementation of pervasive systems, can provide novel functionalities through innovative breakthrough technologies. Some of the areas of application of the IoT are smart homes, smart cities, smart factories, agriculture, and healthcare [3]. Although some solutions of IoT systems have been carried out in the healthcare field, there are some challenges and open problems that need to be addressed, such as standardization, IoT healthcare platforms, the app development process, scalability, continuous monitoring, and data protection [4].