Example hardcoding an existing VPC

existing-vpc.tf

# Create a subnet to launch our instances into
resource "aws_subnet" "default" {
  vpc_id                  = "<EXISTING VPC ID HERE>"
  cidr_block              = "10.0.1.0/24"
  map_public_ip_on_launch = true
}

# Our default security group to access
# the instances over SSH and HTTP
resource "aws_security_group" "default" {
  name        = "terraform_sg_default"
  description = "Used in the terraform"
  vpc_id      = "<EXISTING VPC ID HERE>"

  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  ingress {
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  ingress {
    from_port   = 8443
    to_port     = 8443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  ingress {
    from_port   = 30000
    to_port     = 35000
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  ingress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    self = true
  }

  # outbound internet access
  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

output "subnet" {
  value = "${aws_subnet.default.id}"
}

output "security_group" {
  value = "${aws_security_group.default.id}"
}