Connecting remote states together
Up until now, we naively stored all of our Terraform code in a single repository. We had a single template responsible for creating a network, routes, virtual machines, security groups, and everything else. It works pretty well, provided you have a single application with modest infrastructure around it. A single VPC, a few subnets, a small database, and a couple of instances: with this scale, there are few reasons to go beyond the single repository for all the infrastructure templates.
If you are part of a large organization, this approach can get you only so far. Companies that heavily rely on AWS tend to have dozens of use cases for many, various services. Only the IAM service has quite a few entities to manage: roles, policies, users, groups, and so on. Normally, there are many roles for different servers and even more policies for these roles. The network is also kind of complicated; at the very least, you would have one VPC per environment or even one...
