`load_balancing_algorithm_type` behaves incorrectly when added/removed.

[lizthegrey]

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Terraform Version

Terraform/0.12.23 TFC/402a0ad321

Provider Version

v2.52.0

Affected Resource(s)

• aws_alb_target_group

Terraform Configuration Files

First, create:

resource "aws_alb_target_group" "shepherd_alb_tg" {
  name                          = "shepherd-${var.env}-alb-tg"
  target_type                   = "instance"
  load_balancing_algorithm_type = "least_outstanding_requests"
  port                          = 8080
  protocol                      = "HTTP"
  vpc_id                        = var.vpc_id
}

Then roll back to (notice the removed load_balancing_algorithm_type field):

resource "aws_alb_target_group" "shepherd_alb_tg" {
  name        = "shepherd-${var.env}-alb-tg"
  target_type = "instance"
  port        = 8080
  protocol    = "HTTP"
  vpc_id      = var.vpc_id
}

Debug Output

n/a

Panic Output

n/a

Expected Behavior

  # module.kibble_asgs.aws_alb_target_group.shepherd_alb_tg will be updated in-place
  ~ resource "aws_alb_target_group" "shepherd_alb_tg" {
        arn                                = "arn:aws:elasticloadbalancing:us-east-1:702835727665:targetgroup/shepherd-kibble-alb-tg/63d1693fa2fca1b2"
        arn_suffix                         = "targetgroup/shepherd-kibble-alb-tg/63d1693fa2fca1b2"
        deregistration_delay               = 300
        id                                 = "arn:aws:elasticloadbalancing:us-east-1:702835727665:targetgroup/shepherd-kibble-alb-tg/63d1693fa2fca1b2"
        lambda_multi_value_headers_enabled = false
      ~ load_balancing_algorithm_type      = "least_outstanding_requests" -> "round_robin"
        name                               = "shepherd-kibble-alb-tg"
        port                               = 8080
        protocol                           = "HTTP"
        proxy_protocol_v2                  = false
        slow_start                         = 0
        tags                               = {}
        target_type                        = "instance"
        vpc_id                             = "vpc-f1ea198a"
    }

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

Actual Behavior

No changes. Infrastructure is up-to-date.

Steps to Reproduce

1. terraform apply to create an ALB target group with load_balancing_algorithm_type set to the non-default of least_outstanding_requests
2. terraform apply to remove the load_balancing_algorithm_type parameter

Important Factoids

n/a

References

• 11141 (introduced the new load_balancing_algorithm_type parameter but didn't correctly restore it to defaults if not present)

• 11019

• 11039

[nijave]

Just ran into this. I suspect it's because that field should be using a default instead of being "computed"

                       "load_balancing_algorithm_type": {
                Type:     schema.TypeString,
                Optional: true,
                Computed: true,
                ValidateFunc: validation.StringInSlice([]string{
                    "round_robin",
                    "least_outstanding_requests",
                }, false),
            },

[justinretzolk]

Hey @lizthegrey 👋 Thank you for taking the time to file this! Given that there's been a number of AWS Provider releases since you initially filed it, can you confirm whether you're still experiencing this behavior?

[lizthegrey]

Just ran into this. I suspect it's because that field should be using a default instead of being "computed"

                       "load_balancing_algorithm_type": {
              Type:     schema.TypeString,
              Optional: true,
              Computed: true,
              ValidateFunc: validation.StringInSlice([]string{
                  "round_robin",
                  "least_outstanding_requests",
              }, false),
          },

As per this, I believe because there is still no Default: "round_robin", at https://github.com/hashicorp/terraform-provider-aws/blob/187f1659a4fef11ac314567273b5470afe6b662f/internal/service/elbv2/target_group.go#L132 that the bug still exists and should be reproducible with the repro instructions I gave. However, it is not a priority for us to repro as we are not using least_outstanding_requests and flipping it back and forth at the moment.