How to create multiple instances with multiple subnet ids using terraform?

Question

I have 2 services test1,test2 and for each service i have to create 6 vm's.This 6 vm's should be placed in 3 subnet id's which created in 3 different zones in a same region

In this services,test1 will be in private subnets and test2 will be in public subnets.So i have to pass that correct subnet id when creating ec2 instances

root module:

provider "aws" {
  region = var.region
}

module "ecom-vpc" {
  source = "./modules/vpc"
}

module "ecom-public-subnet" {
  source = "./modules/subnets/public"
  vpc-id = module.ecom-vpc.vpc-id
}

module "ecom-private-subnet" {
  source = "./modules/subnets/private"
  vpc-id = module.ecom-vpc.vpc-id
}

module "ecom-instances-sg" {
  source = "./modules/sg"
  vpc-id = module.ecom-vpc.vpc-id
}

module "ecom-vm-instances" {
  source = "./modules/vm"
  priv-subnet-ids = module.ecom-private-subnet.ecom_private_subnets
  pub-subnet-ids = module.ecom-public-subnet.ecom_public_subnets
  instances-sg = module.ecom-instances-sg.ecom-inst-sg
}

From child modules - vpc,subnets,ec2

variable "service-names" {
  type    = list(any)
  default = ["ecom-app-TEST1","ecom-app-TEST2"]

}

variable "availability_zones" {
  type = map
  default = {
    ap-south-1a = {
      private_subnet = "10.0.1.0/24"
      public_subnet  = "10.0.4.0/24"
    }
    ap-south-1b = {
      private_subnet = "10.0.2.0/24"
      public_subnet  = "10.0.5.0/24"
    }
    ap-south-1c = {
      private_subnet = "10.0.3.0/24"
      public_subnet  = "10.0.6.0/24"
    }
      }
  }

resource "aws_vpc" "ecom-vpc" {
  cidr_block = var.ecom-cidr
}

output "vpc-id" {
  value = aws_vpc.ecom-vpc.id
}

resource "aws_subnet" "ecom-private" {
  for_each = var.availability_zones
  vpc_id                  = var.vpc-id
  cidr_block              = each.value.private_subnet
  availability_zone       = each.key
  map_public_ip_on_launch = false
  tags = {
    Name = "${split("-", each.key)[2]}"
    Subnet_Type = "private"
  }
}

output "ecom_private_subnets" {
  value = aws_subnet.ecom-private
}

resource "aws_subnet" "ecom-public" {
  for_each = var.availability_zones
  vpc_id                  = var.vpc-id
  cidr_block              = each.value.public_subnet
  availability_zone       = each.key
  map_public_ip_on_launch = true
  tags = {
    Name = "${split("-", each.key)[2]}"
    Subnet_Type = "public"
  }
  depends_on = [aws_internet_gateway.igw
  ]
}

  
output "ecom_public_subnets" {
  value = aws_subnet.ecom-public
}

I'm trying to achieve the same by creating a locals which combines service names,priv,public subnet id's,instance count(2).But the problem is i'm not able to make it because i'm not able to create a unique combination of keys

locals {
 service_subnets = {
    for pair in setproduct(var.service-names, values(var.priv-subnet-ids),values(var.pub-subnet-ids),range(var.instance_count)) :
    "${pair[0]}:${pair[1].availability_zone}-${pair[3]}" => {
      service_name = pair[0]
      priv-subnet       = pair[1]
      pub-subnet = pair[2]
    }
  }
}


 resource "aws_instance" "ecom-instances" {
  for_each = local.service_subnets
  ami           = data.aws_ami.ecom.id
  instance_type = "t3.micro"
  tags = {
    Name = each.value.service_name
    Service = each.value.service_name
  }

  vpc_security_group_ids = [var.instances-sg[each.value.service_name].id]
  subnet_id  = "${split("-", each.value.service_name)[2] == "TEST1" ? each.value.pub-subnet.id  : each.value.priv-subnet.id }"
}

I'm getting the below error.

Two different items produced the key "ecom-app-TEST1:ap-south-1c-1" in this 'for' expression. If duplicates are expected, use the ellipsis (...)
│ after the value expression to enable grouping by key.

If i add ... and change it as below then it is converted as tuple and i'm not sure how to get and pass the value from each.value in the aws_instance resource

   locals {
     service_subnets = {
        for pair in setproduct(var.service-names, values(var.priv-subnet-ids),values(var.pub-subnet-ids),range(var.instance_count)) :
        "${pair[0]}:${pair[1].availability_zone}-${pair[3]}" => {
          service_name = pair[0]
          priv-subnet       = pair[1]
          pub-subnet = pair[2]
        }
     ... }
    }

on modules/vm/main.tf line 60, in resource "aws_instance" "ecom-instances":
│   60:   subnet_id  = "${split("-", each.value.service_name)[2] == "TEST1" ? each.value.pub-subnet.id  : each.value.priv-subnet.id }"
│     ├────────────────
│     │ each.value is tuple with 3 elements
│ 
│ This value does not have any attributes.

Please Guide me

To help people help you, perhaps you should provide the definitions of the variables you use in the definition of the local (var.priv-subnet-ids, etc...). — RafaP
@RafaP everything is separate module.Thats why i'm unable to give details.Now i added root,child module code also.Will pass the output from each module — JPNagarajan
I'm afraid pasting lots of code does not help (at least it doesn't help me, I don't have time to do your job...) What I am suggesting you do is simply use the variable definitions of var.priv-subnet-ids and var.pub-subnet-ids, plug them into the expression that gives you the error and do some debugging; if still not working, ask again — RafaP

Paul Stanley Paul Stanley · Accepted Answer · 2021-05-30T19:05:33

You could try adding the index to your for loop and making it part of your name, might help you avoid elipsis/tuple conversion.

locals {
 service_subnets = {
    for index, pair in setproduct(var.service-names, values(var.priv-subnet-ids),values(var.pub-subnet-ids),range(var.instance_count)) :
    "${pair[0]}:${pair[1].availability_zone}-${pair[3]}=${index}" => {
      service_name = pair[0]
      priv-subnet       = pair[1]
      pub-subnet = pair[2]
    }
  }
}

How to create multiple instances with multiple subnet ids using terraform?

root module:

From child modules - vpc,subnets,ec2

1 Answers