fix: update subnet group to fix name vs name_prefix (#312)

README.md

@@ -100,15 +100,26 @@ module "db" {
 
 ## Conditional creation
 
-There is also a way to specify an existing database subnet group and parameter group name instead of creating new resources like this:
+The following values are provided to toggle on/off creation of the associated resources as desired:
 
 ```hcl
-# This RDS instance will be created using default database subnet and parameter group
 module "db" {
   source = "terraform-aws-modules/rds/aws"
 
-  db_subnet_group_name = "default"
-  parameter_group_name = "default.mysql5.7"
+  # Disable creation of RDS instance(s)
+  create_db_instance = false
+
+  # Disable creation of option group - provide an option group or default AWS default
+  create_db_option_group = false
+
+  # Disable creation of parameter group - provide a parameter group or default to AWS default
+  create_db_parameter_group = false
+
+  # Disable creation of subnet group - provide a subnet group
+  create_db_subnet_group = false
+
+  # Enable creation of monitoring IAM role
+  create_monitoring_role = true
 
   # ... omitted
 }
@@ -147,6 +158,44 @@ Users have the ability to:
   option_group_name = "prod-instance-postgresql-11.0" # this will be ignored, no option group created
 ```
 
+- Use a default option group provided by AWS
+
+```hcl
+  create_option_group = false
+```
+
+## Parameter Groups
+
+[Reference](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithParamGroups.html)
+
+Users have the ability to:
+
+- Create a parameter group with the name provided:
+
+```hcl
+  parameter_group_name            = "prod-instance-mysql-8.0"
+  parameter_group_use_name_prefix = false
+```
+
+- Create a parameter group using a unique prefix beginning with the name provided:
+
+```hcl
+  parameter_group_name = "prod-instance-mysql-8.0"
+```
+
+- Pass the name of a parameter group to use that has been created outside of the module:
+
+```hcl
+  create_parameter_group = false
+  parameter_group_name   = "prod-instance-mysql-8.0" # must already exist in AWS
+```
+
+- Use a default parameter group provided by AWS
+
+```hcl
+  create_parameter_group = false
+```
+
 ## Examples
 
 - [Complete RDS example for MSSQL](https://github.com/terraform-aws-modules/terraform-aws-rds/tree/master/examples/complete-mssql)
@@ -206,7 +255,9 @@ No resources.
 | create\_db\_parameter\_group | Whether to create a database parameter group | `bool` | `true` | no |
 | create\_db\_subnet\_group | Whether to create a database subnet group | `bool` | `true` | no |
 | create\_monitoring\_role | Create IAM role with a defined name that permits RDS to send enhanced monitoring metrics to CloudWatch Logs. | `bool` | `false` | no |
+| db\_subnet\_group\_description | Description of the DB subnet group to create | `string` | `""` | no |
 | db\_subnet\_group\_name | Name of DB subnet group. DB instance will be created in the VPC associated with the DB subnet group. If unspecified, will be created in the default VPC | `string` | `""` | no |
+| db\_subnet\_group\_use\_name\_prefix | Determines whether to use `subnet_group_name` as is or create a unique name beginning with the `subnet_group_name` as the prefix | `bool` | `true` | no |
 | delete\_automated\_backups | Specifies whether to remove automated backups immediately after the DB instance is deleted | `bool` | `true` | no |
 | deletion\_protection | The database can't be deleted when this value is set to true. | `bool` | `false` | no |
 | domain | The ID of the Directory Service Active Directory domain to create the instance in | `string` | `""` | no |

main.tf

 locals {
-  create_db_subnet_group = var.db_subnet_group_name == "" ? var.create_db_subnet_group : false
-  db_subnet_group_name   = var.db_subnet_group_name != "" ? var.db_subnet_group_name : module.db_subnet_group.this_db_subnet_group_id
+  db_subnet_group_name = coalesce(var.db_subnet_group_name, module.db_subnet_group.this_db_subnet_group_id)
 
   parameter_group_name_id = var.create_db_parameter_group ? module.db_parameter_group.this_db_parameter_group_id : var.parameter_group_name
 
@@ -11,9 +10,11 @@ locals {
 module "db_subnet_group" {
   source = "./modules/db_subnet_group"
 
-  create      = local.create_db_subnet_group
-  identifier  = var.identifier
-  name_prefix = "${var.identifier}-"
+  create = var.create_db_subnet_group
+
+  name            = coalesce(var.db_subnet_group_name, var.identifier)
+  use_name_prefix = var.db_subnet_group_use_name_prefix
+  description     = var.db_subnet_group_description
   subnet_ids      = var.subnet_ids
 
   tags = var.tags

modules/db_subnet_group/README.md

@@ -29,10 +29,11 @@ No Modules.
 | Name | Description | Type | Default | Required |
 |------|-------------|------|---------|:--------:|
 | create | Whether to create this resource or not? | `bool` | `true` | no |
-| identifier | The identifier of the resource | `string` | n/a | yes |
-| name\_prefix | Creates a unique name beginning with the specified prefix | `string` | n/a | yes |
+| description | The description of the DB subnet group | `string` | `""` | no |
+| name | The name of the DB subnet group | `string` | `""` | no |
 | subnet\_ids | A list of VPC subnet IDs | `list(string)` | `[]` | no |
 | tags | A mapping of tags to assign to the resource | `map(string)` | `{}` | no |
+| use\_name\_prefix | Determines whether to use `name` as is or create a unique name beginning with `name` as the specified prefix | `bool` | `true` | no |
 
 ## Outputs
 

modules/db_subnet_group/main.tf

+locals {
+  name        = var.use_name_prefix ? null : var.name
+  name_prefix = var.use_name_prefix ? "${var.name}-" : null
+
+  description = coalesce(var.description, format("%s subnet group", var.name))
+}
+
 resource "aws_db_subnet_group" "this" {
   count = var.create ? 1 : 0
 
-  name_prefix = var.name_prefix
-  description = "Database subnet group for ${var.identifier}"
+  name        = local.name
+  name_prefix = local.name_prefix
+  description = local.description
   subnet_ids  = var.subnet_ids
 
   tags = merge(
     var.tags,
     {
-      "Name" = format("%s", var.identifier)
+      "Name" = var.name
     },
   )
 }
-

modules/db_subnet_group/variables.tf

@@ -4,14 +4,22 @@ variable "create" {
   default     = true
 }
 
-variable "name_prefix" {
-  description = "Creates a unique name beginning with the specified prefix"
+variable "name" {
+  description = "The name of the DB subnet group"
   type        = string
+  default     = ""
 }
 
-variable "identifier" {
-  description = "The identifier of the resource"
+variable "use_name_prefix" {
+  description = "Determines whether to use `name` as is or create a unique name beginning with `name` as the specified prefix"
+  type        = bool
+  default     = true
+}
+
+variable "description" {
+  description = "The description of the DB subnet group"
   type        = string
+  default     = ""
 }
 
 variable "subnet_ids" {

variables.tf

@@ -110,12 +110,6 @@ variable "vpc_security_group_ids" {
   default     = []
 }
 
-variable "db_subnet_group_name" {
-  description = "Name of DB subnet group. DB instance will be created in the VPC associated with the DB subnet group. If unspecified, will be created in the default VPC"
-  type        = string
-  default     = ""
-}
-
 variable "availability_zone" {
   description = "The Availability Zone of the RDS instance"
   type        = string
@@ -223,6 +217,30 @@ variable "tags" {
 }
 
 # DB subnet group
+variable "create_db_subnet_group" {
+  description = "Whether to create a database subnet group"
+  type        = bool
+  default     = true
+}
+
+variable "db_subnet_group_name" {
+  description = "Name of DB subnet group. DB instance will be created in the VPC associated with the DB subnet group. If unspecified, will be created in the default VPC"
+  type        = string
+  default     = ""
+}
+
+variable "db_subnet_group_use_name_prefix" {
+  description = "Determines whether to use `subnet_group_name` as is or create a unique name beginning with the `subnet_group_name` as the prefix"
+  type        = bool
+  default     = true
+}
+
+variable "db_subnet_group_description" {
+  description = "Description of the DB subnet group to create"
+  type        = string
+  default     = ""
+}
+
 variable "subnet_ids" {
   description = "A list of VPC subnet IDs"
   type        = list(string)
@@ -303,12 +321,6 @@ variable "options" {
   default     = []
 }
 
-variable "create_db_subnet_group" {
-  description = "Whether to create a database subnet group"
-  type        = bool
-  default     = true
-}
-
 variable "create_db_instance" {
   description = "Whether to create a database instance"
   type        = bool