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ELB classic load balancers should be configured with defensive or strictest desync mitigation mode

This control checks whether a Classic Load Balancer is configured with defensive or strictest desync mitigation mode. This control will fail if the Classic Load Balancer is not configured with defensive or strictest desync mitigation mode.

How to fix

Attribute desync_mitigation_mode of aws_elb must be one of: "defensive", "strictest".

Implementation options

Choose the option that matches how you manage Terraform. All options satisfy this control.

Use the compliance.tf registry module to get this control enforced by default. This control is mapped to the frameworks shown in the tabs above. To begin, see get started with compliance.tf.

module "elb" {
  source  = "acscessentialeight.compliance.tf/terraform-aws-modules/elb/aws"
  version = ">=4.0.0,<5.0.0"

  health_check = {
    healthy_threshold   = 2
    interval            = 30
    target              = "HTTP:80/"
    timeout             = 5
    unhealthy_threshold = 2
  }
  listener = [
    {
      instance_port     = 80
      instance_protocol = "HTTP"
      lb_port           = 80
      lb_protocol       = "HTTP"
    }
  ]
  name            = "my-elb"
  security_groups = ["sg-12345678"]
  subnets         = ["subnet-12345678"]
}

module "elb" {
  source  = "pcidssv321.compliance.tf/terraform-aws-modules/elb/aws"
  version = ">=4.0.0,<5.0.0"

  health_check = {
    healthy_threshold   = 2
    interval            = 30
    target              = "HTTP:80/"
    timeout             = 5
    unhealthy_threshold = 2
  }
  listener = [
    {
      instance_port     = 80
      instance_protocol = "HTTP"
      lb_port           = 80
      lb_protocol       = "HTTP"
    }
  ]
  name            = "my-elb"
  security_groups = ["sg-12345678"]
  subnets         = ["subnet-12345678"]
}

module "elb" {
  source  = "pcidss.compliance.tf/terraform-aws-modules/elb/aws"
  version = ">=4.0.0,<5.0.0"

  health_check = {
    healthy_threshold   = 2
    interval            = 30
    target              = "HTTP:80/"
    timeout             = 5
    unhealthy_threshold = 2
  }
  listener = [
    {
      instance_port     = 80
      instance_protocol = "HTTP"
      lb_port           = 80
      lb_protocol       = "HTTP"
    }
  ]
  name            = "my-elb"
  security_groups = ["sg-12345678"]
  subnets         = ["subnet-12345678"]
}

Option 2: Open source module (terraform-aws-modules)

If you use terraform-aws-modules/elb/aws, configure the required module inputs to satisfy this control. You can later migrate to the compliance.tf module with minimal changes because it is compatible by design.

module "elb" {
  source  = "terraform-aws-modules/elb/aws"
  version = ">=4.0.0,<5.0.0"

  health_check = {
    healthy_threshold   = 2
    interval            = 30
    target              = "HTTP:80/"
    timeout             = 5
    unhealthy_threshold = 2
  }
  listener = [
    {
      instance_port     = 80
      instance_protocol = "HTTP"
      lb_port           = 80
      lb_protocol       = "HTTP"
    }
  ]
  name            = "my-elb"
  security_groups = ["sg-12345678"]
  subnets         = ["subnet-12345678"]

  desync_mitigation_mode = "defensive"
}

Option 3: Terraform AWS provider resources

If you manage resources directly, configure the relevant Terraform AWS provider resources to meet this control. See docs for the resources involved: aws_elb.

resource "aws_elb" "this" {
  availability_zones = ["us-east-1a", "us-east-1b"]

  listener {
    instance_port     = 80
    instance_protocol = "http"
    lb_port           = 80
    lb_protocol       = "http"
  }

  desync_mitigation_mode = "defensive"
}
Which option should I choose?
  • Compliance.tf module (recommended): controls enforced by default and mapped to frameworks.
  • Open source module (terraform-aws-modules): compatible by design with compliance.tf. Same variable names for an easy, low-change migration path when you are ready.
  • Terraform AWS provider resources: manage Terraform resources directly.

Tool mappings

Use these identifiers to cross-reference this control across tools, reports, and evidence.

  • Compliance.tf (CTF) Control: elb_classic_lb_desync_mitigation_mode

  • AWS Config Managed Rule: CLB_DESYNC_MODE_CHECK

  • Checkov Check: CKV_AWS_328

  • Powerpipe Control: aws_compliance.control.elb_classic_lb_desync_mitigation_mode