Reusing terraform modules

Terraform Providers Google
1

I am using the following terraform module to create GCP firewall rules.

I have defined my calling definition by using the definition from below link.

https://registry.terraform.io/modules/terraform-google-modules/network/google/latest/submodules/firewall-rules

the definition looks as follows:

##main.tf
module "fw1" {
source        = "../../modules/fw"

 project = var.project
 network = var.network
 rules = var.rules
}

  ##fw.tfvars
 // instance varaibles
 project        = "gcp-33218"
 network     = "https://www.googleapis.com/compute/v1/projects/gcp-33218/global/networks/default"

 rules = [{
    name                    = "fwr-allow-ssh-ingress"
    description             = null
    direction               = "INGRESS"
    priority                = null
    ranges                  = ["0.0.0.0/0"]
    source_tags             = null
    source_service_accounts = null
    target_tags             = null
    target_service_accounts = null
     allow = [{
       protocol = "tcp"
       ports    = ["80"]
     }]
   }]

  ##variables.tf
  variable "project" {}
  variable "network" {}

  variable "rules" {
     description = "List of custom rule definitions (refer to variables file for syntax)."
     default     = []
     type = list(object({
          name                    = string
          description             = string
          direction               = string
          priority                = number
          ranges                  = list(string)
          source_tags             = list(string)
          source_service_accounts = list(string)
          target_tags             = list(string)
          target_service_accounts = list(string)
                allow = list(object({
                    protocol = string
                    ports    = list(string)
                  }))
                }))
            }

I was able to create a firewall rule successfully using the above terraform definition (terraform plan -var-file=fw.tfvars).

Now I tried to create another firewall rule by calling same module again in main.tf and creating a separate fw2.tfvars file for variable declaration. The new definition are as follows:

    ##main.tf
    module "fw1" {
    source        = "../../modules/fw"
    project = var.project
    network = var.network

    rules = var.rules
   }

    module "fw2" {
    source        = "../../modules/fw"
    project = var.project
    network = var.network
    rules = var.rules
    }

   ##fw2.tfvars
  // instance varaibles
  project        = "gcp-33218"
  network     = "https://www.googleapis.com/compute/v1/projects/gcp-33218/global/networks/default"

  rules = [{
      name                    = "fwr-allow-https-ingress"
      description             = null
      direction               = "INGRESS"
      priority                = null
      ranges                  = ["192.168.0.0/29"]
      source_tags             = null
      source_service_accounts = null
      target_tags             = null
      target_service_accounts = null
       allow = [{
          protocol = "tcp"
          ports    = ["80","443"]
           }]
        }]

But when I do a terraform plan -var-file=fw2.tfvars it tries to destroy the existing firewall rule I created earlier .

    # module.fw1.google_compute_firewall.rules["fwr-allow-ssh-ingress"] will be destroyed
  - resource "google_compute_firewall" "rules" {
  - creation_timestamp      = "2021-08-07T02:39:04.190-07:00" -> null
  - destination_ranges      = [] -> null
  - direction               = "INGRESS" -> null
  - disabled                = false -> null
  - id                      = "projects/project-id/global/firewalls/fwr-allow-ssh-ingress" -> null
  - name                    = "fwr-allow-ssh-ingress" -> null
  - network                 = "https://www.googleapis.com/compute/v1/projects/project-id/global/networks/default" -> null
  - priority                = 1000 -> null
  - project                 = "gcp-infrastructure-319318" -> null
  - self_link               = "https://www.googleapis.com/compute/v1/projects/project-id/global/firewalls/fwr-allow-ssh-ingress" -> null
  - source_ranges           = [
      - "0.0.0.0/0",
    ] -> null
  - source_service_accounts = [] -> null
  - source_tags             = [] -> null
  - target_service_accounts = [] -> null
  - target_tags             = [] -> null

  - allow {
      - ports    = [
          - "80",
        ] -> null
      - protocol = "tcp" -> null
    }
}

   # module.fw2.google_compute_firewall.rules["fwr-allow-https-ingress"] will be created
+ resource "google_compute_firewall" "rules" {
  + creation_timestamp = (known after apply)
  + destination_ranges = (known after apply)
  + direction          = "INGRESS"
  + enable_logging     = (known after apply)
  + id                 = (known after apply)
  + name               = "fwr-allow-https-ingress"
  + network            = "https://www.googleapis.com/compute/v1/projects/<project id>/global/networks/default"
  + priority           = 1000
  + project            = (known after apply)
  + self_link          = (known after apply)
  + source_ranges      = [
      + "192.168.0.0/29",
    ]

  + allow {
      + ports    = [
          + "80",
          + "443",
        ]
      + protocol = "tcp"
    }
   }

   Plan: 2 to add, 0 to change, 1 to destroy.

Also why it is trying to add the same resource twice ?

Please suggest so that I create new firewall rules without destroying the rules created earlier using terraform