terraform/examples/aws-networking/subnet/subnet.tf

resource "aws_subnet" "main" {
  cidr_block = "${cidrsubnet(data.aws_vpc.target.cidr_block, 4, lookup(var.az_numbers, data.aws_availability_zone.target.name_suffix))}"
  vpc_id     = "${var.vpc_id}"
  availability_zone = "${var.availability_zone}"
}

resource "aws_route_table" "main" {
  vpc_id = "${var.vpc_id}"
}

resource "aws_route_table_association" "main" {
  subnet_id      = "${aws_subnet.main.id}"
  route_table_id = "${aws_route_table.main.id}"
}