Only set monitoring_role_arn if monitoring_interval > 0

README.md

@@ -4,7 +4,7 @@ A Terraform module to create an Amazon Web Services (AWS) PostgreSQL Relational
 
 ## Usage
 
-```javascript
+```hcl
 module "postgresql_rds" {
   source = "github.com/azavea/terraform-aws-postgresql-rds"
   vpc_id = "vpc-20f74844"
@@ -40,6 +40,18 @@ module "postgresql_rds" {
 }
 ```
 
+### Note about Enhanced Monitoring support
+
+If the `monitoring_interval` passed as an input to this module is `0`, an empty `monitoring_role_arn` value will be threaded into the `aws_db_instance` resource. 
+
+This is because, if a value for `monitoring_role_arn` is threaded into an `aws_db_instance`, along with a `monitoring_interval` of `0`, the following error will occur:
+
+```bash
+InvalidParameterCombination: You must specify a MonitoringInterval value other than 0 when you specify a MonitoringRoleARN value.
+```
+
+If you're curious to know more, see the discussion within terraform-providers/terraform-provider-aws#315.
+
 ## Variables
 
 - `vpc_id` - ID of VPC meant to house database
@@ -92,4 +104,3 @@ module "postgresql_rds" {
 - `endpoint` - Public DNS name and port separated by a `:`
 - `hosted_zone_id` - The zone id for the autogenerated DNS name given in `endpoint`. 
    Use this when creating a short-name DNS [alias](https://www.terraform.io/docs/providers/aws/r/route53_record.html#alias-record) for the `endpoint` 
-

main.tf

@@ -73,7 +73,7 @@ resource "aws_db_instance" "postgresql" {
   parameter_group_name       = "${var.parameter_group}"
   storage_encrypted          = "${var.storage_encrypted}"
   monitoring_interval        = "${var.monitoring_interval}"
-  monitoring_role_arn        = "${aws_iam_role.enhanced_monitoring.arn}"
+  monitoring_role_arn        = "${var.monitoring_interval > 0 ? aws_iam_role.enhanced_monitoring.arn : ""}"
 
   tags {
     Name        = "DatabaseServer"