aws_elasticloadbalancingv2: Incorrect statement that NLB health check healthy/unhealthy counts need to be the same

[vcschapp]

Describe the issue

The documentation for the unhealthyThresholdCount member of the ELBv2 HealthCheck interface says that for NLBs the unhealthy threshold count must be the same as the healthy threshold count:

unhealthyThresholdCount?

Type: number (optional, default: 2)

The number of consecutive health check failures required before considering a target unhealthy.

For Application Load Balancers, the default is 2. For Network Load Balancers, this value must be the same as the healthy threshold count.

This does not appear to be accurate.

• When I create an NLB target group manually in the AWS EC2 console and configure the health check manually, I can set the healthy/unhealthy counts to different values.
• There is no reference to this limitation in the CloudFormation documentation for AWS::ElasticLoadBalancingV2::TargetGroup or any of its member attributes.
• There is no attempt to validate this constraint in the CDK TypeScript code.

Links

1. Impacted CDK documentation page: https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_elasticloadbalancingv2.HealthCheck.html#unhealthythresholdcount
2. Documentation source in GitHub. https://github.com/aws/aws-cdk/blob/v2.170.0/packages/aws-cdk-lib/aws-elasticloadbalancingv2/lib/shared/base-target-group.ts#L135-L136
3. Relevant CloudFormation documentation: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-elasticloadbalancingv2-targetgroup.html#cfn-elasticloadbalancingv2-targetgroup-unhealthythresholdcount

CDK Version

Last checked in documentation for v2.170.0.

[khushail]

Hi @vcschapp , thanks for reporting this.

I see that on the AWS Docs page, both the range is mentioned as 2-10 while the defaults differ in case of both UnhealthyThresholdCount and HealthyThresholdCount (https://docs.aws.amazon.com/elasticloadbalancing/latest/network/target-group-health-checks.html) -

and the same is mentioned in Cloudformation docs as well -https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-elasticloadbalancingv2-targetgroup.html#cfn-elasticloadbalancingv2-targetgroup-healthythresholdcount

So it might be misleading to write such statement in CDK doc and should be corrected -

aws-cdk/packages/aws-cdk-lib/aws-elasticloadbalancingv2/lib/shared/base-target-group.ts

Line 136 in a95560c

* Balancers, this value must be the same as the healthy threshold count.

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