Last night (June 8th, 2021), there was scheduled maintenance at the datacenter in Dallas, where they had to de-energize each of their power distribution circuits for maintenance. The first one they de-energized, at 10:35 pm, went normally, as all of the devices we installed there have dual redundant power supplies. That circuit came back up at 11:21 pm, and no subscriber traffic had been affected by the power outage at all. The next circuit they de-energized, at 11:35 pm, had no impact on almost all of the equipment, with one exception: the edge router which connects our network to the internet.
Apparently, the second of its redundant power supplies had failed, and the specific design of this unit meant it did not report this information to us, so when it needed to rely on that power supply for power, the power supply was unable to provide any, and that router simply shut down. Unfortunately, there was nothing we could have done at that point but wait for power to be restored, which occurred at 12:27 am, and as soon as the sole working power supply in that router came back online, so too did our network reconnect to the internet.
During the outage, our phone system and email system were also unable to reach the internet, as they are located inside our network as well.
This was a bit of a freak occurrence, as the data center has power redundancy and battery backups. This specific event occurred because of routine maintenance on those redundant power systems, so it is unlikely to recur for many years, and we will be replacing that unit with one which does have working dual redundant power supplies before the next maintenance window occurs.