[capableweb]

> I don’t think you need two servers to do zero downtime upgrades

Absolutely not and I can't understand why I keep hearing this argument. Doing zero downtime upgrades on a single server have been simple since basically forever, run another process on another port, change config, restart front balancer gracefully and there you go.

[bagels]

Sure, it can be done, but that alone isn't enough reason to give up redundancy.