At present I am using a monolithic setup with 1 stack for an entire environment. For a number of reasons it would be handy to separate and have a base environment created in 1 stack and we able to then deploy other stacks using the resources of the base stack. As a concrete example, assume a base stack creates and EC2 public and private subnet, a bastion server, nat instance and a few other pieces. Then I would like to create a new stack to put an application server in the public subnet. What is the best way to reference the resources of the existing stack?