feat(ec2): default BastionHostLinux to use Amazon Linux 2023 (under feature flag)

[blimmer]

Issue #29493

Closes #29493

Reason for this change

Right now, if a machineImage property isn't passed to BastionHostLinux, it defaults to an Amazon Linux 2 image. Since Amazon Linux 2 is hitting end-of-life in June 2025, it'd be better to default to Amazon Linux 2023.

Since changing this default would be a breaking change, I placed it behind a feature flag, @aws-cdk/aws-ec2:bastionHostUseAmazonLinux2023ByDefault.

Description of changes

• Added the @aws-cdk/aws-ec2:bastionHostUseAmazonLinux2023ByDefault
• When set, and a machineImage is not provided, we use the latest Amazon Linux 2023 image, instead of Amazon Linux 2.

Description of how you validated changes

• Unit Tests
• Integration Test

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

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[blimmer]

I updated the old integration tests, since AL2023 is the new default with the feature flag on. I added an integration test disabling the flag, which can be removed when v3 is released.

[tmokmss]

LGTM, thanks!

[blimmer]

Merge conflicts resolved.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.50%. Comparing base (9e6bb24) to head (b94afc2).

Additional details and impacted files

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##             main   #31996   +/-   ##
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  Coverage   78.50%   78.50%           
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  Files         106      106           
  Lines        7201     7201           
  Branches     1321     1321           
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  Hits         5653     5653           
  Misses       1361     1361           
  Partials      187      187           

Flag	Coverage Δ
suite.unit	78.50% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	78.50% <ø> (ø)

[GavinZZ]

LGTM, thank you for this high quality work!

[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]

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: b94afc2
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[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).

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