I got this error when upgrading to 3.3.0 on my pre-prod instance. In pre-prod I can just stop the server and run that command but I would like to keep the production instance up.

# WARNING:
# Your Fleet database is missing required migrations. This is likely to cause...
# Run '/app/fleet prepare db' to perform migrations.

Is it safe to run

/app/fleet (with fleet 3.3.0) prepare db

when an older version is running live or will I need to turn off prod for a short time while I swap it to 3.3.0?

See https://github.com/fleetdm/fleet/blob/master/docs/infrastructure/updating-fleet.md#running-database-migrations

cool, thank you!