It definitely is possible...provided that nobody uses it. You don't get charged for data transfer between instances on the same data region, so you could archit

It definitely is possible...provided that nobody uses it. You don't get charged for data transfer between instances on the same data region, so you could architect the system in a way that takes advantage of that. The problem becomes dealing with the outside world. Once you have users then there is a chance that they would push the one instance that is acting as a portal to the outside world out of the free tier.