How to create multiple ec2 instance across different subnets and Az zones with private ip address - amazon-ec2

Question

I have a slight issue. I have 3 subnet cidr blocks with 3 different az groups. I am passing a list of static Ip address for these instance to get assigned in order. My code however is throwing "ip address is out of range for the subnet" which makes sense because it's just going from ip 0 to the N instance how can i properly make sure the instance gets placed in the proper subnet. I hope my question makes sense and is clear please see the code below thank you all for the help! The code belows creates the instance
### Start of Radient FID Server ###
resource "aws_instance" "FID" {
depends_on = [aws_kms_key.aws-wm-wmad-prod]
disable_api_termination = false
count = var.How_many_FID
ami = var.windows_dc_ami_2016
availability_zone = element(var.availability_zones, count.index)
ebs_optimized = var.windows_dc_ebs_optimized
instance_type = var.windows_dc_instance_type_FID
key_name = var.Key_Pair_Ec2
monitoring = true
vpc_security_group_ids = [aws_security_group.Private01.id]
subnet_id = element(aws_subnet.private_subnet_cidr_blocks_Apps, count.index).id
private_ip = "${lookup(var.ips,count.index)}"
associate_public_ip_address = false
tags = merge(
{
Name = element(var.Radiant_FID_Server_Tags, count.index)
Project = var.project,
Environment = var.environment
},
var.tags
)
I have a variables file which i'm passing the private Ip addresses:
variable "ips" {
default = {
"0" = "10.7.90.79"
"1" = "10.7.90.80"
"2" = "10.7.90.81"
"3" = "10.7.90.82"
"4" = "10.7.90.90"
"5" = "10.7.90.84"
"6" = "10.7.90.85"
"7" = "10.7.90.86"
"8" = "10.7.90.87"
"9" = "10.7.90.88"
}
}
##how i create my subnets
resource "aws_subnet" "private_subnet_cidr_blocks_AD" {
count = length(var.private_subnet_cidr_blocks_AD) # count = 3
vpc_id = aws_vpc.default.id #id34odfjdf
cidr_block = var.private_subnet_cidr_blocks_AD[count.index]
availability_zone = var.availability_zones[count.index]
tags = merge(
{
Name = element(var.private_subnet_cidr_blocks_AD_NameTag, count.index),
Project = var.project,
Environment = var.environment
},
var.tags
)
}

Answer 1

So let's say you have the following CIDR block list defined:
private_subnet_cidr_blocks_AD = ["10.7.90.64/27", "10.7.90.96/27","10.7.90.160/27"]
Then you could define your IP list like this:
variable "ips" {
default = [
{ subnet=0, ip="10.7.90.79" },
{ subnet=0, ip="10.7.90.80" },
{ subnet=0, ip="10.7.90.81" },
# etc...
{ subnet=1, ip="10.7.90.100" },
{ subnet=1, ip="10.7.90.101" },
# etc...
{ subnet=2, ip="10.7.90.170" },
{ subnet=2, ip="10.7.90.171" },
]
}
Each subnet number being the index in the private_subnet_cidr_blocks_AD list that corresponds to the CIDR block that the IP belongs to.
Then your instance definition could look like this:
resource "aws_instance" "FID" {
for_each = toset( var.ips )
subnet_id = aws_subnet.private_subnet_cidr_blocks_Apps[each.value.subnet].id
private_ip = each.value.ip