Depends on what the backend systems were doing. They may have been data feeds that could be cached, with the “front-end” actually being a whole app with its own

Depends on what the backend systems were doing. They may have been data feeds that could be cached, with the “front-end” actually being a whole app with its own back end and database. Or perhaps taking orders and queueing them up for later delivery when the back-end systems came back on line.