Appendix B. An illustrated example
This appendix demonstrates a hands-on approach to Reactive system design, illustrating the tenets of the Manifesto through concrete examples. We encounter these while solving issues that come up when building applications that are scalable to a global user base. Globally distributed interaction is also at the heart of the example problem we will tackle here: you will build an app with which users can share their location in real time and in which they can watch others move on a map. An extension to this core function is that users can exchange text messages with other users in their vicinity.
To be more precise, the location of each individual is used for two purposes:
- Each user can share their location with a set of other users who can track it on a map.
- Each user can share their location in anonymized form so that aggregated data can be displayed to all users (such as, “37 users per hour moving westward on highway 50 through Dodge City, Kansas”).