For example, I'd like to query a Postgres DB from a workflow, and I need to add a network ACL to expose port 5432 to a limited set of IPs. So I'd like to know the IP address(es) from which the request will come.

Ideally, this would be provided in a publicly-accessible data exchange format (for example, AWS provides theirs as a JSON doc), so I can update firewall or network rules programmatically.