aws-batch: deprecated useOptimalInstanceClasses property is still needed

[rjuengling-hf]

Describe the bug

Issue #35515 / release 2.220 deprecated property useOptimalInstanceClasses of managed compute environments. But this option is still needed if users want to avoid including optimal in a compute environment's instance types.

Please remove the deprecation warning for use of this property, or change its default to false.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Library Version

2.219

Expected Behavior

No deprecation warning.

Current Behavior

Deprecation warning when use useOptimalInstanceClasses.

Reproduction Steps

Synthesize a cdk stack with a Batch compute environment and setting useOptimalInstanceClasses.

Possible Solution

Revert the deprecation.

Additional Information/Context

No response

AWS CDK Library version (aws-cdk-lib)

2.220

AWS CDK CLI version

2.1033.0

Node.js Version

22.18.0

OS

AL2023

Language

Python

Language Version

3.11

Other information

No response

[pahud]

Hi @rjuengling-hf,

Thank you for reporting this issue. After analyzing the code, this appears to be a valid concern about the deprecation of useOptimalInstanceClasses.

The current implementation in the renderInstances function shows that 'optimal' is automatically added to the instance types when:

• useOptimalInstanceClasses is true or undefined (default)
• defaultInstanceClasses is not provided or empty

The only way to prevent 'optimal' from being included is to explicitly set useOptimalInstanceClasses = false, which now triggers a deprecation warning. The new defaultInstanceClasses property provides a way to add the new default instance classes (default_x86_64 and default_arm64), but it doesn't provide a mechanism to explicitly exclude all default/optimal classes when you want to use only custom instance types.

This creates a gap where users who want to specify only their own instance types/classes have no non-deprecated way to exclude optimal.

Possible solutions:

1. Remove the deprecation from useOptimalInstanceClasses since it serves a legitimate use case
2. Enhance the logic to treat an explicitly empty defaultInstanceClasses array as "exclude all defaults"
3. Change the default behavior (breaking change)

I believe the most pragmatic approach would be to remove the deprecation warning from useOptimalInstanceClasses, as it provides explicit control over a behavior that isn't fully covered by the new defaultInstanceClasses property. But the final decision would be on the maintainer from PR review.

We welcome PRs to get it fixed.