reboot required by apt
This check indicates that some packages have been installed but cannot be activated without rebooting the machines.
The check contains a list of apps that require a reboot (click into the warning for the list)
See the rebooting machines for what to do.
If there are a high number of machines requiring a reboot, including ones that are not part of database clusters (such as Mongo and MySQL machines) there may be a problem with the locking mechanism.
Check if this is the case using Fabric:
fab <environment> all locksmith.status
If there is a lock in place it will detail which machine holds the lock. You can remove it with:
fab <environment> -H <machine-name> locksmith.unlock:"<machine-name>"
Machines which are safe to reboot should then do so at the scheduled time.