[Bug]: elasticloadbalancing:ModifyLoadBalancerAttributes api error ValidationError: An action must be specified

[robh007]

Terraform Core Version

1.9.2

AWS Provider Version

5.74.0

Affected Resource(s)

When trying to modify either an existing LB listener with attribute tcp_idle_timeout_seconds or when you've created a new LB Listener with the attribute included, subsequent modifications fail with the following error.

operation error Elastic Load Balancing v2: ModifyListener, https response error StatusCode: 400, RequestID: 9443d8b7-fc7f-4de0-b831-878f907e6d5f, api error ValidationError: An action must be specified

The tests look only to create either the GWLB or NLB, there isn't a test to then modify the attribute.

Expected Behavior

Listener attribute tcp_idle_timeout_seconds should be modified with appropriate value

Actual Behavior

Error with API call.

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

resource "aws_lb" "test" {
  name               = "test-gwlb"
  load_balancer_type = "gateway"
  subnet_mapping {
    subnet_id = "subnet-1234567"
  }

  tags = {
    Name = "test-gwlb"
  }
}

resource "aws_lb_target_group" "test" {
  name     = "test-target-group"
  port     = 6081
  protocol = "GENEVE"
  vpc_id   = aws_vpc.test.id

  health_check {
    enabled             = true
    interval            = 30
    path                = "/"
    port                = "traffic-port"
    protocol            = "HTTP"
    timeout             = 5
    healthy_threshold   = 3
    unhealthy_threshold = 3
  }

  tags = {
    Name = "test-target-group"
  }
}

resource "aws_lb_listener" "test" {
  load_balancer_arn = aws_lb.test.arn
  port              = 6081
  protocol          = "GENEVE"
  tcp_idle_timeout_seconds = 3600

  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.test.arn
  }

  tags = {
    Name = "test-listener"
  }
}

Steps to Reproduce

Run terraform to create the resources
Modify the following attribute on the listener

tcp_idle_timeout_seconds = 60

Run terraform to modify & the error will occur.

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

None

[github-actions]

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[jar-b]

Relates #39585

[github-actions]

Warning

This issue has been closed, meaning that any additional comments are hard for our team to see. Please assume that the maintainers will not see them.

Ongoing conversations amongst community members are welcome, however, the issue will be locked after 30 days. Moving conversations to another venue, such as the AWS Provider forum, is recommended. If you have additional concerns, please open a new issue, referencing this one where needed.

[github-actions]

This functionality has been released in v5.75.0 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.