CDK generating empty targets for CfnCrawler - aws-cdk

Question

I'm using CDK Python API to define a Glue crawler, however, the CDK generated template contains empty 'Targets' block in the Crawler resource.
I've not been able to find an example to emulate. I've tried varying the definition of the targets object, but the object definition seems to be ignored by CDK.
from aws_cdk import cdk
BUCKET='poc-1-bucket43879c71-5uabw2rni0cp'
class PocStack(cdk.Stack):
def __init__(self, app: cdk.App, id: str, **kwargs) -> None:
super().__init__(app, id)
from aws_cdk import (
aws_iam as iam,
aws_glue as glue,
cdk
)
glue_role = iam.Role(
self, 'glue_role',
assumed_by=iam.ServicePrincipal('glue.amazonaws.com'),
managed_policy_arns=['arn:aws:iam::aws:policy/service-role/AWSGlueServiceRole']
)
glue_crawler = glue.CfnCrawler(
self, 'glue_crawler',
database_name='db',
role=glue_role.role_arn,
targets={"S3Targets": [{"Path": f'{BUCKET}/path/'}]},
)
I expect the generated template to contain a valid 'targets' block with a single S3Target. However, cdk synth outputs a template with empty Targets in the AWS::Glue::Crawler resource:
gluecrawler:
Type: AWS::Glue::Crawler
Properties:
DatabaseName: db
Role:
Fn::GetAtt:
- glueroleFCCAEB57
- Arn
Targets: {}

Answer 1

Resolved, thanks to a clever colleague!
Changing "S3Targets" to "s3Targets", and "Path" to "path" resolved the issue. See below.
Hi Bob,
When I use typescript, the following works for me:
new glue.CfnCrawler(this, 'glue_crawler', {
databaseName: 'db',
role: glue_role.roleArn,
targets: {
s3Targets: [{ path: "path" }]
}
}
When I used Python, the following appears working too:
glue_crawler = glue.CfnCrawler(
self, 'glue_crawler',
database_name='db',
role=glue_role.role_arn,
targets={
"s3Targets": [{ "path": f'{BUCKET}/path/'}]
},
)
In Typescript, TargetsProperty is an interface with s3Targets as a property. And in
s3Targets, path is a property as well. I guess during the JSII transformation, it forces
us to use the same names in Python instead of the initial CFN resource names.

Answer 2

A more general way to approach this problem is to dig inside the cdk library in 2 steps:
1.
from aws_cdk import aws_glue
print(aws_glue.__file__)
(.env/lib/python3.8/site-packages/aws_cdk/aws_glue/__init__.py)
Go to that file and see how the mapping/types are defined. As of 16 Aug 2020, you find
#jsii.data_type(
jsii_type="#aws-cdk/aws-glue.CfnCrawler.TargetsProperty",
jsii_struct_bases=[],
name_mapping={
"catalog_targets": "catalogTargets",
"dynamo_db_targets": "dynamoDbTargets",
"jdbc_targets": "jdbcTargets",
"s3_targets": "s3Targets",
}
)
I found that the lowerCamelCase always work, while the pythonic snake_case does not.