sample.tf

# Define the Terraform source module to use: an RDS database module in this example
terraform {
  source = "git::git@github.com:terraform-aws-modules/terraform-aws-rds?ref=v2.13.0"
}
# Define dependencies
dependency "vpc" {
  config_path = "../path/to/vpc_module"
}
dependency "sg" {
  config_path = "../path/to/security_group_module"
}
dependency "some_other_dep" {
  config_path = "../other/variables/for/making/an/RDS_database"
}
# Terraform modules have ‘variables’ that need to be populated before that 
# module can be run. In Terraform, these are provided by a static file.
# In Terragrunt, this `input` block can be used to dynamically supply those variables!
inputs = {
  identifier = "backend"
  db_subnet_group_name   = dependency.vpc.outputs.database_subnet_group
  vpc_security_group_ids = [dependency.sg.outputs.this_security_group_id]
  other_necessary_variables = dependency.some_other_dep.outputs.any_output
}