Real Telco OpenStack upgrade lessons learned

Queens release was the first one which addressed OpenStack problem of upgrades between relatively frequent releases. Fast Forward Upgrade (FFU), Skip Upgrade or (N+3) upgrade are the terms describe the same thing, upgrade from OpenStack Newton to OpenStack Queens. We are now a year after Queens release and it may be a good time to look again on the N+3 upgrade,when Telcos are scheduling to perform upgrades on their own infrastructure and understand the complexity of these upgrades. In Telco worl