[Nextgrid]

You use the spare that's next to it, failing that, in a desperate situation, go to any computer store, buy the biggest gaming PC you can find, load it up with RAM and use that. It'll work, your customers won't know nor care.

In practice, I wouldn't recommend colocation until you are at the scale and budget where you can maintain your own spares. Better outsource it to a dedicated host like OVH/Hetzner/etc that has tons of servers and can immediately replace the hardware.