Remove EIP allocation (#29)

Author: int128

README.md

@@ -41,6 +41,13 @@ module "nat" {
   private_subnets_cidr_blocks = module.vpc.private_subnets_cidr_blocks
   private_route_table_ids     = module.vpc.private_route_table_ids
 }
+
+resource "aws_eip" "nat" {
+  network_interface = module.nat.eni_id
+  tags = {
+    "Name" = "nat-instance-main"
+  }
+}
 ```
 
 Now create an EC2 instance in the private subnet to verify the NAT configuration.
@@ -55,12 +62,13 @@ This module provisions the following resources:
 
 - Auto Scaling Group with mixed instances policy
 - Launch Template
-- Elastic IP
 - Elastic Network Interface
 - Security Group
 - IAM Role for SSM and ENI attachment
 - VPC Route (optional)
 
+You need to attach your elastic IP to the ENI.
+
 Take a look at the diagram:
 
 ![diagram](diagram.svg)
@@ -119,6 +127,24 @@ resource "aws_security_group_rule" "nat_ssh" {
 ```
 
 
+## Migration guide
+
+### Upgrade to v2 from v1
+
+This module no longer creates an EIP since v2.
+
+To keep your EIP when you migrate to module v2, rename the EIP in the state as follows:
+
+```console
+% terraform state mv -dry-run module.nat.aws_eip.this aws_eip.nat
+Would move "module.nat.aws_eip.this" to "aws_eip.nat"
+
+% terraform state mv module.nat.aws_eip.this aws_eip.nat
+Move "module.nat.aws_eip.this" to "aws_eip.nat"
+Successfully moved 1 object(s).
+```
+
+
 ## Contributions
 
 This is an open source software. Feel free to open issues and pull requests.
@@ -152,14 +178,11 @@ No requirements.
 | user\_data\_runcmd | Additional runcmd section of cloud-init | `list` | `[]` | no |
 | user\_data\_write\_files | Additional write\_files section of cloud-init | `list` | `[]` | no |
 | vpc\_id | ID of the VPC | `string` | n/a | yes |
-| eip_creation | Whether to create an eip | `bool` | `true` | no | 
 
 ## Outputs
 
 | Name | Description |
 |------|-------------|
-| eip\_id | ID of the Elastic IP |
-| eip\_public\_ip | Public IP of the Elastic IP for the NAT instance |
 | eni\_id | ID of the ENI for the NAT instance |
 | eni\_private\_ip | Private IP of the ENI for the NAT instance |
 | iam\_role\_name | Name of the IAM role for the NAT instance |

example/example.tf

@@ -41,6 +41,13 @@ module "nat" {
   ]
 }
 
+resource "aws_eip" "nat" {
+  network_interface = module.nat.eni_id
+  tags = {
+    "Name" = "nat-instance-example"
+  }
+}
+
 # IAM policy for port forwarding (optional)
 resource "aws_iam_role_policy" "dnat_service" {
   role   = module.nat.iam_role_name
@@ -72,5 +79,5 @@ resource "aws_security_group_rule" "dnat_http" {
 }
 
 output "nat_public_ip" {
-  value = module.nat.eip_public_ip
+  value = aws_eip.nat.public_ip
 }

main.tf

@@ -31,12 +31,6 @@ resource "aws_network_interface" "this" {
   tags              = local.common_tags
 }
 
-resource "aws_eip" "this" {
-  count             = var.enabled ? var.eip_creation ? 1 : 0 : 0
-  network_interface = aws_network_interface.this.id
-  tags              = local.common_tags
-}
-
 resource "aws_route" "this" {
   count                  = length(var.private_route_table_ids)
   route_table_id         = var.private_route_table_ids[count.index]

outputs.tf

@@ -1,13 +1,3 @@
-output "eip_id" {
-  description = "ID of the Elastic IP"
-  value       = var.enabled ? var.eip_creation ? aws_eip.this[0].id : "" : ""
-}
-
-output "eip_public_ip" {
-  description = "Public IP of the Elastic IP for the NAT instance"
-  value       = var.enabled ? var.eip_creation ? aws_eip.this[0].public_ip : "" : ""
-}
-
 output "eni_id" {
   description = "ID of the ENI for the NAT instance"
   value       = aws_network_interface.this.id

variables.tf

@@ -71,11 +71,6 @@ variable "user_data_runcmd" {
   type        = list
   default     = []
 }
-variable "eip_creation" {
-  description = "Whether to create an elastic ip"
-  type        = bool
-  default     = true
-}
 
 locals {
   // Generate common tags by merging variables and default Name