In terms of installing into an existing environment, a lot will depend on what already exists there and how you want to grant access to it. The simplest case would probably be to just Terraform some VMs that run a Vault cluster, a set of Boundary controllers and one or more Boundary workers into your existing VPCs and subnets – that will get you an installation you can start configuring and building on as needed. The details are so highly variable though, that I think it might be hard to provide a ready-to-use set of Terraform files you can just deploy.
That said… I may take a whack at doing so later tonight as it fits into a long-term model I’m working on for demoing Boundary. I’ll let you know if I come up with anything that looks like it might be useful.