At 4:09PM Monday, May 7th Canvas Support announced a 10 minute maintenance they must conduct on May 22nd @4:00AM. Their original message follows.
Canvas Status Update
Scheduled maintenance on 5/22/2018 at 2:00 AM MST (8:00 AM UTC)
We’ll be performing a brief maintenance event on your Canvas instance on Tuesday, May 22nd. We anticipate this event will last 10 minutes; it will occur during the 30-minute interval between 2:00 AM MST (4:00AM EST) / 8:00 AM UTC and 2:30 AM MST (4:30AM EST), and your users will not be able to access Canvas while the event is underway.
We know that the timing of this event isn’t ideal, given that it falls near the end of a semester for many institutions. The work we’ll do is to apply a critical security update, and Amazon Web Services reserves the right to apply it themselves at a time of their choosing if we do not apply it soon. We are opting to move forward on our own schedule, since we can at least ensure that the event happens in the wee hours of the morning. Please contact your customer success manager if you have any questions or concerns.