Isn't it usually a bad idea to have the database and application server in different data centers? It is / was my understanding that both the database and application server should ideally be on the same rack.
It's really just a matter of latency and bandwidth costs. If you can tolerate both, then keeping them in different data centers is fine. In fact, depending on your architecture, you may have to do this at some point anyway, even within the same cloud provider.