fix(ec2-alpha): addInternetGW handles shared route table for subnets

[shikha372]

Issue # (if applicable)

Closes #33672

Reason for this change

Earlier same routes were being added to shared route table between subnets causing deployment failures.

Description of changes

• Added helper method to unique we don't process single route table twice.
• Also added return value for IGW and EIGW so that customers can refer them to as target later, similar to other gateway and endpoints.

Describe any new or updated permissions being added

NA

Description of how you validated changes

Added unit test and integration test

Limitation for adding integration test for IPv6, we don't know the AmazonprovidedIPv6 before for which local route gets added and needs to be added in expected assertion.

Error: Resolution error: Resolution error: Resolution error: Found an encoded list token string in a scalar string context. Use 'Fn.select(0, list)' (not 'list[0]') to extract elements from token lists.

        {
          DestinationCidrBlock: vpc.ipv6CidrBlocks[0],
          GatewayId: 'local',
        },

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.98%. Comparing base (1c5cbfa) to head (9be81a6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #33824   +/-   ##
=======================================
  Coverage   83.98%   83.98%           
=======================================
  Files         120      120           
  Lines        6976     6976           
  Branches     1178     1178           
=======================================
  Hits         5859     5859           
  Misses       1005     1005           
  Partials      112      112           

Flag	Coverage Δ
suite.unit	83.98% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	83.98% <ø> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[aws-cdk-automation]

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[paulhcsun]

Just one question, otherwise looks good.

[paulhcsun]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

[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).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 9be81a6
• Result: SUCCEEDED
• Build Logs (available for 30 days)

Powered by github-codebuild-logs, available on the AWS Serverless Application Repository

[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).

[github-actions]

Comments on closed issues and PRs are hard for our team to see.
If you need help, please open a new issue that references this one.