Espresso can run in a very small footprint. In Amazon, many servers are "micro" instances -- part of one CPU and 600MB of RAM.
When installing Espresso on your own hardware or in your own cloud, we recommend:
Most critical is the round-trip time to your database(s). The closer Espresso is to the database(s), the better. Ideally, the ping time between the Espresso machine(s) and the database server(s) should be less than 1ms. You can test this in the Espresso Designer (Test database).