  Digital health applications that leverage multiple sources of patient data
for insights to patients' behaviours or disease symptoms as well as remote
patient monitoring, nudging and treatments are becoming increasingly popular in
various medical practices and research. One common issue among these
applications is that they are generally based on project-specific solutions and
developed from scratch. Such application development fashion results in large
amounts of repetitive effort, for example, in building study specific websites
and mobile frontends, deploying customised infrastructures, and collecting data
that may have already been collected in other studies and projects. What is
worse, the data collected, and functions built cannot be easily reused by other
applications. In this paper, we present an event-driven microservice platform,
namely DHLink, to address this issue. DHLink securely links existing digital
health applications of different projects, facilitates real-time data sharing,
and supports rapid application development by reusing data and functions of
existing digital health applications. In addition, comes with DHLink, a set of
highly generic and reusable microservices is provided, which allows developers
to rapidly create a typical above-mentioned digital health application by only
developing the core algorithms. Two use cases outlined in this paper have shown
the use of DHLink and the set of microservices for application collaboration
and new application development to be efficient and practical.
