instance_type_replica not honoured

[svenlito]

Description

When creating a cluster where instance_type is set, instance_type_replica is ignored and instance_type is used for replica instances.

I believe this was introduced here #211

Reproduction

Steps to reproduce the behavior:

create autoscaling example with instance_type and instance_type_replica defined.

Expected behavior

instance_type_replica to be honoured.

Actual behavior

instance_type_replica uses instance_type value

[rnrsr]

When creating a cluster where instance_type is set, instance_type_replica is ignored and instance_type is used for replica instances.

@svenlito I think this is intentional, from the instance_type description here: https://registry.terraform.io/modules/terraform-aws-modules/rds-aurora/aws/latest?tab=inputs
it says:

If instance_type_replica is not set it will use the same type for replica instances

If you want different types used on your read replicas specify the instance_type_replica like so, i just tried it on 5.2.0:

  replica_count                = 2
  instance_type                = "db.t3.small"
  instance_type_replica        = "db.t3.medium"

gives me:

  # module.rds_my.module.rds-cluster.aws_rds_cluster_instance.this[0] will be updated in-place
  ~ resource "aws_rds_cluster_instance" "this" {
        id                              = "my-1"
      ~ instance_class                  = "db.r5.large" -> "db.t3.small"
      ~ performance_insights_enabled    = true -> false
        tags                            = {
            "Environment" = "dev"
            "Terraform"   = "true"
        }
        # (25 unchanged attributes hidden)
    }

  # module.rds_my.module.rds-cluster.aws_rds_cluster_instance.this[1] will be updated in-place
  ~ resource "aws_rds_cluster_instance" "this" {
        id                              = "my-2"
      ~ instance_class                  = "db.r5.large" -> "db.t3.medium"
      ~ performance_insights_enabled    = true -> false
        tags                            = {
            "Environment" = "dev"
            "Terraform"   = "true"
        }
        # (25 unchanged attributes hidden)
    }

[svenlito]

@rnrsr what I found is that whether I remove the instance_type_replica attribute or update it, my state doesn't change and it's stuck with whatever I've set instance_type to be. The example you're showing works because you're also changing the value of instance_type.

[rnrsr]

I don't think that's accurate, if i just try changing the instance_type_replica based on the above example, i get:

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:

  # module.rds_my.module.rds-cluster.aws_rds_cluster_instance.this[1] will be updated in-place
  ~ resource "aws_rds_cluster_instance" "this" {
        id                              = "my-2"
      ~ instance_class                  = "db.r5.large" -> "db.t3.medium"
        tags                            = {
            "Environment" = "dev"
            "Terraform"   = "true"
        }
        # (26 unchanged attributes hidden)
    }

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

So it did ignore the master instance

[svenlito]

I don't think that's accurate, if i just try changing the instance_type_replica based on the above example, i get:

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:

  # module.rds_offers.module.rds-cluster.aws_rds_cluster_instance.this[1] will be updated in-place
  ~ resource "aws_rds_cluster_instance" "this" {
        id                              = "offers-2"
      ~ instance_class                  = "db.r5.large" -> "db.t3.medium"
        tags                            = {
            "Environment" = "dev"
            "Terraform"   = "true"
        }
        # (26 unchanged attributes hidden)
    }

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

I get:

No changes. Infrastructure is up-to-date.

This means that Terraform did not detect any differences between your
configuration and real physical resources that exist. As a result, no
actions need to be performed.

[rnrsr]

╰─❯ terraform version
Terraform v0.14.4
+ provider registry.terraform.io/hashicorp/aws v3.36.0
+ provider registry.terraform.io/hashicorp/null v3.1.0
+ provider registry.terraform.io/hashicorp/random v3.1.0

Your version of Terraform is out of date! The latest version
is 0.15.3. You can update by downloading from https://www.terraform.io/downloads.html

[svenlito]

➔ t version
Terraform v0.14.2
+ provider registry.terraform.io/hashicorp/aws v3.39.0
+ provider registry.terraform.io/hashicorp/random v3.1.0
+ provider registry.terraform.io/hashicorp/vault v2.19.1
+ provider registry.terraform.io/terraform-providers/mysql v1.9.0

Your version of Terraform is out of date! The latest version
is 0.15.3. You can update by downloading from https://www.terraform.io/downloads.html

[rnrsr]

wierd. tried a re-init?

[svenlito]

Doing both, bumping to 0.14.4 and re-init now.

[svenlito]

Doing both, bumping to 0.14.4 and re-init now.

This didn't help.

[rnrsr]

interesting, what replica_count are you using?

i notice this count.index > 0 ? in the commit. Are you trying to reduce the replica_count to 1 at the same time as removing the instance_type_replica?

[svenlito]

interesting, what replica_count are you using?

Currently replica_count = 1

[svenlito]

if replica_count is set to 2 it will create module.production_master.aws_rds_cluster_instance.this[1] with the intended instance_type. Did I misinterprete the docs?

[svenlito]

interesting, what replica_count are you using?

i notice this count.index > 0 ? in the commit. Are you trying to reduce the replica_count to 1 at the same time as removing the instance_type_replica?

Oh, I think this is an off by one type of mistake then..

[svenlito]

I think this should be https://github.com/terraform-aws-modules/terraform-aws-rds-aurora/blob/master/main.tf#L119

instance_class = try(lookup(var.instances_parameters[count.index], "instance_type"), count.index + 1 > 0 ? coalesce(var.instance_type_replica, var.instance_type) : var.instance_type)

[svenlito]

I think #193 is somewhat related

[github-actions]

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