monitoring_role_arn for "aws_db_instance" "this_mssql" resource calculates empty value and generates error in case monitoring_interval > 0

[yxycman]

Terraform: 0.12.25
AWS_provider: 2.70.0
module version: 2.15.0, 2.17.0

During creation of MSSQL backed RDS instance, i am getting the following error:
Error: Error modifying DB Instance db-host: InvalidParameterCombination: A MonitoringRoleARN value is required if you specify a MonitoringInterval value other than 0
as a result of the following interpolation:
var.monitoring_interval > 0 ? coalesce(var.monitoring_role_arn, aws_iam_role.enhanced_monitoring.*.arn, null) : null

For the "aws_db_instance" "this" resource in the same file, monitoring_role_arn is calculated with slightly different interpolation and, if i apply it to resource in question everything works fine
var.monitoring_interval > 0 ? coalesce(var.monitoring_role_arn, join(", ", aws_iam_role.enhanced_monitoring.*.arn), null) : null

looks like the cause is the type of the aws_iam_role.enhanced_monitoring.*.arn item, which is a list and a behavior of the coalesce function in case, more than two arguments provided.

> coalesce("", ["atata", "aaaa"], null)

> coalesce("", join(",", ["atata", "aaaa"]), null)
atata,aaaa
> coalesce("", ["atata", "aaaa"])

>
Error: Error in function call

  on <console-input> line 1:
  (source code not available)

Call to function "coalesce" failed: all arguments must have the same type.

Calling module with:

module "rds" {
  source                              = "terraform-aws-modules/rds/aws"
  version                             = "2.17.0"
  identifier                          = var.identifier
  engine                              = "sqlserver-se"
...
  create_monitoring_role             = true
  monitoring_interval                   = 60
...
}

https://github.com/terraform-aws-modules/terraform-aws-rds/blob/v2.17.0/modules/db_instance/main.tf#L151

[ghost]

Is there any update on the above, looks like version 2.18.0 still has this issue.

Error: Error creating DB Instance: InvalidParameterCombination: A MonitoringRoleARN value is required if you specify a MonitoringInterval value other than 0. [2020-10-05T06:43:47.049Z] status code: 400, request id: 8ad86abc-428f-458e-a84f-8d9a0e631094

[mpardej]

Getting the same error. Is there any update?

[bryantbiggs]

Closed with #318

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