(rds): Make Aurora cluster instance class publicly available

[moltar]

Describe the feature

• The AuroraClusterInstance class is private. Thus, I can't find it in the node tree.
• The static factory methods returns IClusterInstance, which is not helpful and only has the bind method.
• I can't search for the CfnDBInstance instance because every construct ID value is a Resource, and every other prop is a token.

Use Case

Sometimes, I need to get at instance-specific values, such as instance ID, or instance endpoint, e.g. for monitoring purposes.

Proposed Solution

1. Make the AuroraClusterInstance class public and make it discoverable on the cluster.
2. Create the ability to pass the concrete AuroraClusterInstance instance that implements the IClusterInstance as the cluster reader and writer.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

latest

Environment details (OS name and version, etc.)

macOS

[pahud]

Root Cause Analysis

Key design details discovered:

The class AuroraClusterInstance is private:

// AuroraClusterInstance is private, hiding implementation details
class AuroraClusterInstance extends Resource implements IClusterInstance {
  //...
}
The static factory method(s) return only the IClusterInstance interface:
public static instanceType(...) : IClusterInstance {
  return new AuroraClusterInstance(...);
}
The IClusterInstance interface only exposes a minimal API, primarily .bind():
export interface IClusterInstance {
  bind(scope: Construct, cluster: IDatabaseCluster, props: ClusterInstanceBindOptions): ClusterInstanceConfig;
}

This design choice hides the actual properties and methods of the underlying instances, restricting advanced usage.

Current vs Expected

Possible Fixes / Solutions

Increase the visibility of the AuroraClusterInstance class to public:

// Instead of private:
export class AuroraClusterInstance extends Resource implements IClusterInstance {
  //...
}

Or alternatively,

• Expose concrete AuroraClusterInstance instances from factory methods (instead of or alongside interfaces).
• Provide read-only properties on the IClusterInstance interface that expose key values such as instance identifier and endpoint.

This would enable developers to programmatically access instance-specific information, facilitating more sophisticated infrastructure integrations and monitoring.

This makes sense to me and I am requesting for more inputs from the team if there's any concern.