add NAT instance (#169)

* add NAT instance

* added NAT instance types for user to override

* Update templates/terraform/environments/stage/main.tf

Co-authored-by: Bill Monkman <bmonkman@gmail.com>

* Update templates/terraform/environments/stage/main.tf

Co-authored-by: Bill Monkman <bmonkman@gmail.com>

* finalized NAT instance types

Co-authored-by: Bill Monkman <bmonkman@gmail.com>

Author: sshi100

templates/terraform/environments/stage/main.tf

@@ -102,8 +102,12 @@ module "stage" {
 
   domain_name = local.domain_name
 
-  # This will save some money as there a cost associated to each NAT gateway, but if the AZ with the gateway
-  # goes down, nothing in the private subnets will be able to reach the internet. Not recommended for production.
+  # NAT configuration - NAT allows traffic from private subnets to access the public internet
+  
+  ## Instead of using AWS NAT gateway, use a NAT instance which is cheaper by about $30/month, though NAT gateways are more reliable. Only recommended for non-production environments.
+  vpc_enable_nat_gateway = false
+
+  ## When using NAT gateway, setting this to true will save some money as there a cost per-gateway of about $35/month. However, if the AZ with the gateway goes down nothing in the private subnets will be able to reach the internet. Not recommended for production. Not used if `vpc_enable_nat_gateway` is `false`.
   vpc_use_single_nat_gateway = true
 
   # DB configuration

templates/terraform/modules/environment/main.tf

@@ -38,13 +38,15 @@ data "aws_iam_user" "ci_user" {
 
 module "vpc" {
   source  = "commitdev/zero/aws//modules/vpc"
-  version = "0.1.11"
+  version = "0.1.14"
 
   project                 = var.project
   environment             = var.environment
   region                  = var.region
   kubernetes_cluster_name = local.kubernetes_cluster_name
+  enable_nat_gateway      = var.vpc_enable_nat_gateway
   single_nat_gateway      = var.vpc_use_single_nat_gateway
+  nat_instance_types      = var.vpc_nat_instance_types
 }
 
 # To get the current account id

templates/terraform/modules/environment/variables.tf

@@ -68,12 +68,24 @@ variable "db_storage_gb" {
   description = "The amount of storage to allocate for the db, in GB"
 }
 
+variable "vpc_enable_nat_gateway" {
+  description = "Enable nat-gateway"
+  type        = bool
+  default     = true
+}
+
 variable "vpc_use_single_nat_gateway" {
   description = "Use single nat-gateway instead of nat-gateway per subnet"
   type        = bool
   default     = true
 }
 
+variable "vpc_nat_instance_types" {
+   description = "Candidates of instance type for the NAT instance"
+   type        = list
+   default     = ["t3.nano"]
+}
+
 variable "database" {
   default     = "postgres"
   description = "Which database engine to use, currently supports postgres or mysql"