RDS: aws_db_instance not respecting parameter_group_name on first run

[alkema]

When using aws_db_instance and setting the parameter_group_name it is presented in both plan and apply as being set with the correct value. However, after being applied the value is set to something else. When looking at the RDS instance in the AWS interface it is not set properly, it is set to default.mysql5.6, not mysql-params.

Upon an immediate subsequent terraform plan this diff is evident, then a subsequent terraform apply changes parameter_group_name to the correct value. I then need to do an RDS reboot to apply it too.

Terraform Version

✗ terraform -v
Terraform v0.7.0

Affected Resource(s)

• aws_db_instance

Terraform Configuration Files

...
variable "parameter_group_name" {
  default = "mysql-params"
}

resource "aws_db_instance" "default" {
  lifecycle {
    create_before_destroy = true
  }
  instance_class = "${var.instance_class}"
  db_subnet_group_name = "${var.db_subnet_group_name}"
  snapshot_identifier = "${var.snapshot_identifier}"
  identifier = "${var.identifier}"
  parameter_group_name = "${var.parameter_group_name}"
  apply_immediately = true
  tags {
    Cluster = "${var.cluster}"
    Environment = "${var.environment}"
    App = "${var.app}"
  }
}
...

Expected Behavior

I expect parameter_group_name to be applied with the value it was set within the config on first apply. I also expect to have to do an AWS RDS reboot as according to docs:

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.DBInstance.Modifying.html

Parameter group name:
The name change is applied immediately. Any parameter value changes are applied to the DB instance after you manually reboot the DB instance.

Actual Behavior

parameter_group_name is set to default.mysql5.6 not mysql-params.

Steps to Reproduce

terraform plan

...
-/+ module.hampton.aws_db_instance.default
...
    parameter_group_name:       "mysql-params" => "mysql-params"

terraform apply

...
  parameter_group_name:       "" => "mysql-params"
...

terraform plan

Note: this is the only change reported.

~ module.hampton.aws_db_instance.default
    parameter_group_name: "default.mysql5.6" => "mysql-params"

terraform apply

Note: this is the only change reported.

module.hampton.aws_db_instance.default: Modifying...
  parameter_group_name: "default.mysql5.6" => "mysql-params"

Apply complete! Resources: 0 added, 1 changed, 0 destroyed.

Now a manual RDS reboot needed to apply change and finally get a proper parameter_group_name.

[kxseven]

Confirming issue still present in v0.7.7 and v0.7.9.

This issue is especially inconvenient when using (AWS) credentials generated via STS or federated login which normally expire after only 60mins due to the RDS provisioning and modification taking 40+ mins for instances with large amounts of data.

[jhoblitt]

This issue appears to still be present under 0.8.8. In the aws console, it shows the parameter group name correctly but followed by (pending-reboot ). A manual reboot applies the parameter group name change.

[estheban]

Still present in Terraform v0.9.6

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.