How can you write atomic functions so that failures won't have dire consequences? It's easy: use a database that supports transactions. The point of transactions is to guarantee that your data will never be left in a bad state.

If your question is actually how can you make your system continue to function after some hardware fails, then you will have to delve into network architecture and failover technologies, but these don't have much to do with Perl. From the Perl side of things, you just try to do your work and if a transaction fails you handle it in an appropriate way (try again, notify the police, whatever).