[Bug]: r/aws_neptune_cluster_instance: engine_version parameter should be ignored

[triggan]

Terraform Core Version

1.5.7

AWS Provider Version

5.16.2

Affected Resource(s)

• aws_neptune_cluster_instance

Expected Behavior

If a user currently provides the engine_version parameter on an aws_neptune_cluster_instance resource and then goes to perform an engine upgrade of the hosting aws_neptune_cluster that owns that instance, Terraform forces an instance replacement for any affected instances in that cluster.

Engine version upgrades in Neptune are handled at a cluster level, and not at an instance level. All instances in a cluster are required (and forced) to be on the same engine version as the hosting cluster. Upon an engine version upgrade, Neptune will push the latest engine code to each instance and force a reboot of each instance. There is no present requirement to replace all instances in a cluster when performing an engine upgrade.

Per the AWS CLI man page for aws neptune create-db-instance and aws neptune modify-db-instance, the --engine-version parameter is listed as:

       --engine-version (string)
          The version number of the database engine to upgrade to. Currently,
          setting this parameter has no effect. To upgrade your database
          engine to the most recent release, use the
          ApplyPendingMaintenanceAction API.

As such, the aws_neptune_cluster_instance resource schema needs to be altered to mirror this lack of constraint.

Actual Behavior

The current functionality forces an instance replacement after changing the engine_version parameter on both a cluster and all affected instances within the cluster.

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

Initial configuration file:

resource "aws_neptune_cluster" "new_cluster" {
  cluster_identifier = "neptunetestcluster"
  storage_encrypted = true
  engine_version = "1.2.0.1"
  skip_final_snapshot = true
  neptune_cluster_parameter_group_name = "default.neptune1.2"
}

resource "aws_neptune_cluster_instance" "new_instance_1" {
  cluster_identifier = aws_neptune_cluster.new_cluster.id
  engine             = "neptune"
  instance_class     = "db.r5.large"
  engine_version = "1.2.0.1"
  neptune_parameter_group_name = "default.neptune1.2"
}

Steps to Reproduce

After the initial apply, change the engine_version parameters for both resources to 1.2.0.2 and notice that Terraform is asking for the instance to be destroyed and replaced.

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

Yes

[github-actions]

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[justinretzolk]

Related #29785

[github-actions]

This functionality has been released in v5.22.0 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.