Bootstrap: `--region` flag gets ignored by `cdk bootstrap`

[garysassano]

Describe the bug

The CDK CLI silently ignores the --region flag during bootstrapping. It doesn't throw an error or warning, just proceeds as if the flag wasn't provided.

❯ cdk bootstrap --region ap-southeast-1
 ⏳  Bootstrapping environment aws://XXXXXXXXXXXX/ap-southeast-2...
Trusted accounts for deployment: (none)
Trusted accounts for lookup: (none)

Regression Issue

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

Last Known Working CDK Version

No response

Expected Behavior

See above.

Current Behavior

See above.

Reproduction Steps

See above.

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.1018.0

Framework Version

No response

Node.js Version

22.16.0

OS

Ubuntu 24.04

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

Hi @garysassano

After my investigation, the CLI is silently ignoring the global --region flag in multiple scenarios:

Problem Scenarios:

1. Silent ignore with global region only:
   bash
   cdk bootstrap --region ap-southeast-1 # Ignores --region, uses default

2. Silent ignore with conflicting regions:
   bash
   cdk bootstrap aws://123/us-east-1 --region ap-southeast-1 # Should error but doesn't

Root Cause:
The bootstrap method completely ignores global CLI options. Unlike other commands that properly validate conflicting options (like
--execute vs --method), bootstrap has no validation for region conflicts.

Expected Behavior:

• When only --region is specified: Use that region for bootstrap
• When both --region and explicit environment are specified with different regions: Throw an error
• When both match: Work normally

The Fix Should:

1. Add region conflict validation that throws a ToolkitError when --region conflicts with explicit environment regions
2. Use global --region as fallback when no explicit environment is specified
3. Provide clear error messages about the conflict
4. If we don't accept --region, the CLI should throw the error.

This is definitely a bug that needs fixing - the silent ignore behavior is confusing and potentially dangerous. I am making it 1 p1 and bringing it up to the team for review.