Over the course of 2015 and 2016 the system had zero-downtime for all users.
The FL3XX platform is built in the cloud with a cluster of replicas of the entire system. Each copy is hosted in a different location, by a different supplier. Currently we use Amazon Web Services, Vultr, Digital Ocean. Any issue with any site, internet connectivity, our hardware or our software on one instance is transparent to all users: none will see any disruption in the service.
We are constantly improving the system and we now have the very respectable record (since we started counting) of 26 months of uninterrupted service.