peering-root.tf

# snippet from terraform/env-dev/peering.tf

# import staging state, add routes from dev to staging
resource "terraform_remote_state" "staging_state" {
  backend = "s3"
  config {
    bucket = "${var.tf_s3_bucket}"
    region = "${var.region}"
    key = "${var.staging_state_file}"
  }
}

resource "aws_vpc_peering_connection" "its_probably_fine" {
  peer_owner_id = "${var.acct_number}"
  peer_vpc_id = "${terraform_remote_state.staging_state.output.staging_vpc_id}"
  vpc_id = "${module.dev_vpc.vpc_id}"
  auto_accept = "true"

  tags {
    Authored-by = "Ben Hartshorne"
    Idea = "bad"
    But = "ohwell"
    XXX = "what's the worst that can happen?"
    Environment = "development"
    Name = "dev_to_staging_peering"
  }
}

# route to public subnets
resource "aws_route" "dev_to_staging_route" {
  route_table_id = "${module.dev_vpc.public_route_table_id}"
  destination_cidr_block = "${terraform_remote_state.staging_state.output.staging_cidr_block}"
  vpc_peering_connection_id = "${aws_vpc_peering_connection.its_probably_fine.id}"
}

# route *from* dev private subnets to staging
resource "aws_route" "dev_to_staging_int_route" {
  count = "${length(split(",", var.private_ranges))}"
  route_table_id = "${element(split(",", module.dev_vpc.private_route_table_id), count.index)}"
  destination_cidr_block = "${terraform_remote_state.staging_state.output.staging_cidr_block}"
  vpc_peering_connection_id = "${aws_vpc_peering_connection.its_probably_fine.id}"
}

Sorry for ask but, how you implement the route tables in your vpc?