Summary

Fixes the CDK deployment failure in us-west-2 region caused by incorrect Lambda layer region resolution.

Problem

The CDK deployment was failing in us-west-2 with the error:

User: arn:aws:sts::385139013756:assumed-role/cdk-hnb659fds-cfn-exec-role-385139013756-us-west-2/AWSCloudFormation is not authorized to perform: lambda:GetLayerVersion on resource: arn:aws:lambda:us-east-1:615299751070:layer:AWSOpenTelemetryDistroPython:5

This occurred because the code was falling back to the us-east-1 layer ARN instead of using the correct us-west-2 layer ARN.

Root Cause

The issue was in the region detection logic in lambda-petclinic-stack.ts. The original code used:

const regionName = cdk.Stack.of(this).region;
const layerArn = layerArns[regionName] || layerArns['us-east-1']; // Problematic fallback

When CDK tokens weren't resolved properly, this would fall back to us-east-1, causing cross-region layer access attempts.

Solution

1. Improved region detection: Use this.region instead of cdk.Stack.of(this).region for more reliable region resolution
2. Added validation: Ensure the layer ARN exists for the target region before proceeding
3. Enhanced error handling: Throw descriptive errors for unsupported regions instead of silent fallbacks
4. Cross-region validation: Verify that the layer ARN matches the deployment region
5. Added debugging outputs: Include region and layer ARN in CloudFormation outputs for troubleshooting

Changes Made

• Fixed region detection logic to use this.region for better CDK token resolution
• Removed dangerous fallback that could cause cross-region layer access
• Added comprehensive validation to catch region mismatches early
• Enhanced error messages to help users identify unsupported regions
• Added CloudFormation outputs for debugging deployment issues

Testing

This fix ensures that:

• ✅ us-west-2 deployments use the correct layer ARN (arn:aws:lambda:us-west-2:615299751070:layer:AWSOpenTelemetryDistroPython:12)
• ✅ All supported regions use their respective layer ARNs
• ✅ Unsupported regions fail fast with clear error messages
• ✅ No cross-region layer access attempts occur

Impact

• Fixes deployment failures in us-west-2 and other regions
• Prevents silent fallbacks that could cause runtime issues
• Improves error visibility for unsupported regions
• Maintains backward compatibility for all currently supported regions

Fixes #202