Explaining deregistration delay parameter of aws_lb_target_group resource in Terraform

The aim of this page📝 is to explain the deregistration_delay parameter in Terraform based on the particular example of a Terraform plan.

• The deregistration_delay parameter is an optional argument for the aws_lb_target_group resource in Terraform.
• It specifies the amount of time, in seconds, for Elastic Load Balancing to wait before changing the state of a deregistering target from draining to unused.
• The range of values for this parameter is 0–3600 seconds, and the default value is 300 seconds.
• When you remove a target from a target group, Elastic Load Balancing waits for the deregistration_delay timeout to elapse before completing the deregistration process.
• During this time, the target is in the draining state and does not receive any new requests.
• However, it continues to process any requests that were already in flight when the deregistration process began.
• Once the timeout elapses, the target is moved to the unused state and is no longer considered a member of the target group.
• A longer deregistration_delay can be useful if you want to give in-flight requests more time to complete before the target is deregistered.
• This can help to minimize disruption to your users and ensure a smoother transition when you remove targets from the target group.
• On the other hand, a shorter deregistration_delay (or a value of 0) can be useful if you want to quickly remove targets from the target group.
• This can help to webappmize downtime and ensure that your users are quickly routed to healthy targets.
• The choice of value for this parameter depends on your specific use case and requirements.

CODE

Here is a particular example I have experienced with Terraform:

Terraform will perform the following actions:

  ### module.ec2.module.webapp_alb.aws_alb_target_group.alb_tg will be updated in-place
  ~ resource "aws_alb_target_group" "alb_tg" {
      ~ deregistration_delay               = 300 -> 0
        id                                 = "arn:aws:elasticloadbalancing:eu-west-1:000000000000:targetgroup/foo-xxx/000000000000"
        name                               = "foo-000000000000"
        tags                               = {
            "Name"              = "foo-com-example-prod1-webapp-alb"
            "tf_module"         = "aws_ec2_public_alb"
            "tf_module_version" = "1.0.0"
        }
        # (13 unchanged attributes hidden)

        # (2 unchanged blocks hidden)
    }

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

In this specific plan, it appears that the module.ec2.module.webapp_alb.aws_alb_target_group.alb_tg resource will be updated in-place. This means that Terraform will modify the existing resource rather than creating a new one. The only change that will be made is that the deregistration_delay attribute will be changed from 300 to 0. All other attributes and blocks will remain unchanged.

LINKS

• https://www.terraform.io/docs/cli/commands/plan.html