Only one way to do it - and that is the right way.
1) The European Space Operations Centre has two independent connections to the German national grid - one entered the site at one end, one at the other. In addition a massive genset was hired for weeks surrounding critical ops, with living accommodation for the operator. (Yes it was that large).
2) A backup copy of all software and data files was made every day at midnight, encompassing the control centre and the tracking telemetry & command station main computers (STAMACS) spread around the world..
In my 25 years there I only remember one massive failure, which is when an excavator driver dug up the mains supply cable - in the days when there was only one power feed. In fact that incident is why there are two power connections today. Maybe someone here will correct me but I do not remember any major computing/software outages lasting more than an hour, before the system was reloaded and back on line.
Of course we were not trying to cut costs and maximise profits.