CDK: How to get L2 construct instance from L1 (CFN)?

Question

In my CDK code there is a low-lavel ecs.CfnTaskDefinition task definition.

my_task_definition = aws_cdk.ecs.CfnTaskDefinition(
    scope=self,
    id="my_task_definition",
    # rest of the parameters...
)

I want to use this task definition to a create a Ecs service, like this.

my_service = aws_cdk.ecs.Ec2Service(
    scope=self,
    id="my_service",
    cluster=my_cluster,
    task_definition=my_task_definition,  # NOT COMPATIBLE
    desired_count=1,
    # rest of the parameters..
)

But as the task_definition argument of Ec2Service should be an instance of aws_cdk.aws_ecs.TaskDefinition; it’s not possible to use my_task_definition here, which is instance of aws_cdk.aws_ecs.CfnTaskDefinition.

So the question is it possible to get aws_cdk.aws_ecs.TaskDefinition object from aws_cdk.aws_ecs.CfnTaskDefinition instance?

Asked By: Sazzadur Rahman

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Answer 1

Is it possible to get aws_cdk.aws_ecs.TaskDefinition object from aws_cdk.aws_ecs.CfnTaskDefinition instance?

❌ No. You cannot get a L2 Something construct from a L1 CfnSomething. You can get a L2 ISomething interface construct with from_task_definition_arn (see below). But the task_definition prop won’t accept the interface type.

✅ In your case, start with a L2 TaskDefinition or ECSTaskDefinition construct. Then, if you need to muck about with the L1 attributes, use escape hatch syntax to modify its underlying CfnTaskDefinition.

How to get L2 construct instance from L1 (CFN)?

More generally, yes, there are two ways to get a L2 ISomething from a L1 CfnSomething:

(1) The CDK "unescape hatch" syntax, but only for S3 Buckets and KMS keys:

cfnBucket = CfnBucket(stack, 'CfnBucket')
bucket: IBucket = Bucket.from_cfn_bucket(cfn_bucket=cfnBucket)

(2) For other constructs, the from_something_arn reference methods achieve the same result.

Answered By: fedonev

CDK: How to get L2 construct instance from L1 (CFN)?

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