aws_db_instance engine_version gets updated in-place with every run

[Veluu]

Hello,

Whenever auto_minor_version_upgrade is disabled with every terraform apply it wants to do engine_version update in-place.

When auto_minor_version_upgrade is enabled it works as expected.

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Terraform CLI and Terraform AWS Provider Version

Terraform v0.13.5
+ provider registry.terraform.io/hashicorp/aws v3.37.0

Affected Resource(s)

• aws_db_instance

Terraform Configuration Files

Please include all Terraform configurations required to reproduce the bug. Bug reports without a functional reproduction may be closed without investigation.

resource "aws_db_instance" "default" {
  instance_class             = "db.t3.small"
  license_model              = "license-included"
  maintenance_window         = "sun:03:05-sun:05:00"
  engine                     = "oracle-se2"
  engine_version             = "12.1"
  name                       = "EMXPL"
  auto_minor_version_upgrade = false
  allocated_storage          = 10
  username                   = "foo"
  password                   = "foobarbaz"
  skip_final_snapshot        = true
}

Expected Behavior

Configuration has not changed therefore there should be no update in-place. As long as major version is in order (12.1 matches 12.1.x.y.z) there should not be an update.

Actual Behavior

With every run Terraform wants to update engine_version as you can see below. In reality it does nothing as anyway it stays pinned to the newest minor version that's actually available in AWS RDS.

Below there's a plan from second run (after it was first created without any problems).

aws_db_instance.default: Refreshing state... [id=terraform-20210504214948210400000001]

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # aws_db_instance.default will be updated in-place
  ~ resource "aws_db_instance" "default" {
        address                               = "terraform-20210504214948210400000001.ck27w5szo6th.us-east-1.rds.amazonaws.com"
        allocated_storage                     = 10
        arn                                   = "arn:aws:rds:us-east-1:237839530861:db:terraform-20210504214948210400000001"
        auto_minor_version_upgrade            = false
        availability_zone                     = "us-east-1c"
        backup_retention_period               = 0
        backup_window                         = "05:57-06:27"
        ca_cert_identifier                    = "rds-ca-2019"
        character_set_name                    = "AL32UTF8"
        copy_tags_to_snapshot                 = false
        db_subnet_group_name                  = "default"
        delete_automated_backups              = true
        deletion_protection                   = false
        enabled_cloudwatch_logs_exports       = []
        endpoint                              = "terraform-20210504214948210400000001.ck27w5szo6th.us-east-1.rds.amazonaws.com:1521"
        engine                                = "oracle-se2"
      ~ engine_version                        = "12.1.0.2.v23" -> "12.1"
      	# redacted rest of the lines
    }

Plan: 0 to add, 1 to change, 0 to destroy.

Steps to Reproduce

1. terraform apply

• #0000

[obourdon]

Got exactly the same issue with Postgres version specified as major (aka 12), being instantiated during first apply and stored in state file as "12.5" and following plan/apply always want to modify it.

I think that auto_minor_version_upgrade which is a AWS RDS parameter described as follows in the AWS console:

Enable auto minor version upgrade
Enabling auto minor version upgrade will automatically upgrade to new minor versions as they are released. The automatic upgrades occur during the maintenance window for the database.

should be made completely independent of the code here

However, there is a case for which I do not understand how this is really supposed to behave:

Say I specify engine=postgres AND engine_version=12.5 AND auto_minor_version_upgrade=true
what I think will eventually happen is that AWS will at some point in time automatically upgrade my RDS instance to 12.6
However, considering the code mentioned above would then compare 12.5 and 12.6 with the Golang function strings.HasPrefix which will obviously fail too ?

Anything I am missing or getting wrong here ?

[github-actions]

This functionality has been released in v3.54.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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.