Dinamically add resources in Terraform - amazon-web-services

Question

I set up a jenkins pipeline that launches terraform to create a new EC2 instance in our VPC and register it to our private hosted zone on R53 (which is created at the same time) at every run.
I also managed to save the state into S3 so it doesn't fail with the hosted zone being re-created.
the main issue I have is that at every run terraform keeps replacing the previous instance with the new one and not adding it to the pool of instances.
How can avoid this?
here's a snippet of my code
terraform {
backend "s3" {
bucket = "<redacted>"
key = "<redacted>/terraform.tfstate"
region = "eu-west-1"
}
}
provider "aws" {
region = "${var.region}"
}
data "aws_ami" "image" {
# limit search criteria for performance
most_recent = "${var.ami_filter_most_recent}"
name_regex = "${var.ami_filter_name_regex}"
owners = ["${var.ami_filter_name_owners}"]
# filter on tag purpose
filter {
name = "tag:purpose"
values = ["${var.ami_filter_purpose}"]
}
# filter on tag os
filter {
name = "tag:os"
values = ["${var.ami_filter_os}"]
}
}
resource "aws_instance" "server" {
# use extracted ami from image data source
ami = data.aws_ami.image.id
availability_zone = data.aws_subnet.most_available.availability_zone
subnet_id = data.aws_subnet.most_available.id
instance_type = "${var.instance_type}"
vpc_security_group_ids = ["${var.security_group}"]
user_data = "${var.user_data}"
iam_instance_profile = "${var.iam_instance_profile}"
root_block_device {
volume_size = "${var.root_disk_size}"
}
ebs_block_device {
device_name = "${var.extra_disk_device_name}"
volume_size = "${var.extra_disk_size}"
}
tags = {
Name = "${local.available_name}"
}
}
resource "aws_route53_zone" "private" {
name = var.hosted_zone_name
vpc {
vpc_id = var.vpc_id
}
}
resource "aws_route53_record" "record" {
zone_id = aws_route53_zone.private.zone_id
name = "${local.available_name}.${var.hosted_zone_name}"
type = "A"
ttl = "300"
records = [aws_instance.server.private_ip]
depends_on = [
aws_route53_zone.private
]
}
the outcome is that my previously created instance is destroyed and a new one is created. what I want is to keep adding instances with this code.
thank you

Answer 1

Your code creates only one instance aws_instance.server, and any change to its properties will modify that one instance only as your backend is in S3, thus it acts as a global state for each pipeline. The same goes for aws_route53_record.record and anything else in your script.
If you want different pipelines to reuse the same exact script, you should either use different workspaces, or create different TF states for each pipeline. The other alternative is to redefine your TF script to take a map of instances as an input variable and use for_each to create different instances.
If those instances should be same, you should manage their count using using aws_autoscaling_group and desired capacity.