There will be days...
Server
availabilityInternet connectivity: slow to very slow to
non-existent
Electrical power problems: frequent on-battery,
occasional shutdown
System administrators
Security concerns: sudden loss of access to the
server
Unannounced changes, e.g. Domain Name Service reorganizations
Sometimes
at the main site!
Changes that don't get mirrored correctly
Failure to verify that things work on the mirrors