Zuul is an edge service created by Netflix that bases its functionality around filters. Zuul filters follow the interceptor filter pattern (as described at http://www.oracle.com/technetwork/java/interceptingfilter-142169.html). Using filters, you can perform a set of actions on HTTP requests and responses during their routing.
Zuul is the name of a gatekeeper that is taken from a movie (see http://ghostbusters.wikia.com/wiki/Zuul for more details), and represents exactly the functionality that this project has, namely that of a gatekeeper.
You can apply the filter during four phases, as shown in the following diagram:
Zuul ...
