feat(elasticloadbalancingv2): create security group settings for NLB by default (under feature flag)

[badmintoncryer]

Issue # (if applicable)

Closes #34606.

Reason for this change

Currently, CDK's L2 constructs allow setting security groups for NLBs, but this requires explicit configuration.

declare const sg1: ec2.ISecurityGroup;

const lb = new elbv2.NetworkLoadBalancer(this, 'LB', {
  vpc,
  securityGroups: [sg1], // configure SG explicitly
});

This was not originally intended - NLB security group support was implemented later, and the current specification exists to maintain backward compatibility.

#27978
#28494

However, when comparing NLBs without security groups to NLBs with security groups configured, the latter has significantly more advantages. Furthermore, once an NLB is created without security groups, it's impossible to add security group configuration later.

Therefore, I propose using feature flags to make security group configuration the default for NLBs in CDK.

Description of changes

• Add @aws-cdk/aws-elasticloadbalancingv2:networkLoadBalancerWithSecurityGroupByDefault feature flag
• Create security groups by default when feature flags are enabled

Describe any new or updated permissions being added

None

Description of how you validated changes

Add both unit and integ tests

Other information

This implementation was also proposed in the issue, but it was not implemented because it was difficult to detect when referenced from other Connectables as follows case2.

declare const nlb: elbv2.INetworkLoadBalancer;
declare const other: IConnectable;

// case1
nlb.connections.allowTo(other, ec2.Port.tcp(1234));

// case2
other.connections.allowTo(nlb, ec2.Port.tcp(2181));

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[aws-cdk-automation]

AWS CodeBuild CI Report

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• Commit ID: 8cb8370
• Result: FAILED
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[Abogical]

You'll need to run rosetta for the docs.

[Abogical]

Thank you!

[mergify]

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[badmintoncryer]

@Abogical Thank you very much!

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

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[badmintoncryer]

@Mergifyio update

[mergify]

update

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[badmintoncryer]

@Abogical Could you please approve again?

Pull request has been modified.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[Abogical]

@Mergifyio update

[mergify]

update

☑️ Nothing to do, the required conditions are not met

• #commits-behind > 0 [📌 update requirement]
• -closed [📌 update requirement]
• -conflict [📌 update requirement]
• queue-position = -1 [📌 update requirement]

[Abogical]

@Mergifyio requeue

[mergify]

requeue

✅ The queue state of this pull request has been cleaned. It can be re-embarked automatically

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