Modern notification system for Sync and Share using NATS

<!--HTML-->The new CERNBox platform was successfully released for CERN-Wide usage on October 24. It has been quickly adopted by the whole community of about 27.000 users. The platform is comprised of a new Web User Interface based on modern web framework technologies, and a scalable distributed micro-service backend architecture based on Reva. One of the most prevalent feature requests received after the release was to provide users with the means to generate notifications for the different workflows on the platform (e.g., sharing a folder with another user or group, or uploading a file to a shared space). A notification system has been implemented with different types of media (email, web); a templating system for e-mails, a hook system which enables extensibility to all parts of the platform, and a notification center for the web. The notifications service leverages the NATS open-source communication system to enable fast and scalable communication. In this talk we describe the architecture of the new service, the hooks provided to enable developers to add new notifications, and the planned future extensions.