Template error: Fn::Select cannot select nonexistent value at index...

[ThePlenkov]

Describe the feature

Currently when applying template which is using functions like !Select we may have an error like this:

ERROR   2024-05-22 16:14:18    Unexpected error: 
ERROR   2024-05-22 16:14:18    An error occurred (ValidationError) when calling the CreateStack operation: Template error: Fn::Select  cannot select nonexistent value at index 2
ERROR   2024-05-22 16:14:18    CommandExecution failed with exit code: (1)

This is not clear what is going wrong here. We have a large template and it would be great if cdk would print more informative message pointing to the exact place in the file causing the error.

Do you think it's possible? Thanks!

Use Case

Applying published template from yaml file using functions like !Select

Proposed Solution

Printing line number of the template file for the failed function would be already enough. Ideally there must be some debug/trace feature allowing us to debug template execution.

Other Information

No response

Acknowledgements

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

CDK version used

2.142.1 (build ed4e152)

Environment details (OS name and version, etc.)

Ubuntu 23.10

[pahud]

What are you trying to do with that template using CDK? Can you share your CDK code and the commands you executed?

[ThePlenkov]

Well I do something like this:

 new CfnInclude(this, 'solace-task-definition', {
      templateFile: 'solace.template',
      parameters: {
        KeyPairName: keyPairName,
        VPCID: vpc.vpcId,
        PrivateSubnetIDs: taskSubnets.subnetIds,
        PublicSubnetIDs: [],
        SSHSecurityGroupID: sg.securityGroupId,
        RemoteAccessCIDR: '0.0.0.0/0',
        AdminPassword: secret.secretValueFromJson('password').unsafeUnwrap(),
        WorkerNodeInstanceType: `t2.small`,
        MonitorNodeInstanceType: `t2.small`,
        NumberOfAZs: 2,
      },
    });

[ThePlenkov]

in my case I was already able to read the template manually and find the location of !Select function and to review the logic. Currently I was able to solve the error itself. But this ticket is just about the experience. I would prefer if cdk would already pointed me to the exact place in the file which was causing the error.

[pahud]

I would prefer if cdk would already pointed me to the exact place in the file which was causing the error.

Totally agree. Let's make it a feature request for CfnInclude for verbose log.