DATA INTEGRATION SEVICE TO TALK TO DATABASE BEHIND FIREWALL

[woofguk]

Hi !

I'm a newbie in Cloud Computing .
If I have a database (ex:Database A ) in Amazon Cloud and I want to
use somekind of integration service to talk to other database(Database
B) behind a firewall.
My coworker has tried informatica but informatica cannot read database
(Database B) that is located behind firewall.
Is there other data integration software that we can use to talk to a
database that is located behind firewall?
Can you guys suggest me a simple solution to make this two databases
talk to each other?
Sorry If I don't explain it cleary.
Thanks