But it makes sense to retrieve wallets from instances that are going to be permanently deleted (when client stopped paying, etc).

For example it would save 17000 BTC that bitomat.pl exchange lost when upgrading Amazon EC2 instance to add RAM.

Not if you assume that the client should have already backed up data on that instance, and keeping a copy for yourself is illegal.

> lightweight, portable, self-sufficient container that will run virtually anywhere.

It doesn't work on typical cheap VPS servers from http://lowendbox.com/ because they use OpenVZ.

That's where I found the cheap (5gbp per month from NECS) VPS I run my docker instances on. Maybe it is atypical.

It'll certainly work with a cheap Xen or KVM instance but those are usually more expensive.

Digitalocean has a standard docker+ubuntu setup you can fire up for about that price. However, I haven't had much luck with its stability and switched back to running on bare ubuntu. Docker kept bringing the system down even when I wasnt running any containers!

Long-term I expect cheap VPSes to be built on Docker itself because it's more upstream than OpenVZ.

It doesn't run on a typical OpenVZ VPS.

Is there any alternative for separating apps on a single VPS?

Thats because you can't really use the tools the kernel provides which docker uses while in an OpenVZ container.