AWS-UpdateALBDesyncMitigationMode - Amazon Systems Manager Automation runbook reference
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The AWS-UpdateALBDesyncMitigationMode runbook will update the desync mitigation mode on an Application Load Balancer (ALB) to the specified mitigation mode. The desync mitigation mode determines how the load balancer handles requests that might pose a security risk to your application.

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Linux, macOS, Windows


  • AutomationAssumeRole

    Type: String

    Description: (Optional) The Amazon Resource Name (ARN) of the Amazon Identity and Access Management (IAM) role that allows Systems Manager Automation to perform the actions on your behalf. If no role is specified, Systems Manager Automation uses the permissions of the user that starts this runbook.

  • LoadBalancerArn

    Type: String

    Description: (Required) The Amazon Resource Name (ARN) of the ALB that you want to modify the desync mitigation mode of.

  • DesyncMitigationMode

    Type: String

    Valid values: monitor | defensive | strictest

    Description: (Required) The mitigation mode that you want the ALB to use. For information about desync mitigation modes, see Desync mitigation mode in the User Guide for Application Load Balancers.

Required IAM permissions

The AutomationAssumeRole parameter requires the following actions to use the runbook successfully.

  • ssm:StartAutomationExecution

  • ssm:GetAutomationExecution

  • elasticloadbalancing:DescribeLoadBalancers

  • elasticloadbalancing:DescribeLoadBalancerAttributes

  • elasticloadbalancing:ModifyLoadBalancerAttributes

Document Steps

  • VerifyLoadBalancerType (aws:assertAwsResourceProperty) - Verifies that the value specified for the LoadBalancerArn input parameter is for an application load balancer before proceeding to the next step.

  • ModifyLoadBalancerDesyncMode (aws:executeAwsApi) - Updates the ALB to use the specified DesyncMitigationMode.

  • VerifyLoadBalancerDesyncMitigationMode (aws:executeScript) - Verifies that the desync mitigation mode was updated for the target ALB.


VerifyLoadBalancerDesyncMitigationMode.ModificationResult - Message payload of the script verifying the modification to your ALB.