How to Override Logical IDs of Resources in AWS CDK

# Overriding Logical IDs in CDK

Logical IDs serve as unique resource identifiers.

Logical IDs are alphanumeric (A-Za-z0-9) and must be unique in a template.

We set the resource's logical ID in CloudFormation like so:

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Resources:
  # 👇 logical id
  MyLogicalId:
    Type: AWS::DynamoDB::Table
    Properties:
      # ... properties of the table

If we look at a deployed stack, we can see the Logical IDs of resources in the first column:

In order to override the Logical ID of a resource in CDK, we have to use the overrideLogicalId method on the CfnResource.

To be more specific, if we had a CfnBucket resource we would use its overrideLogicalId method.

In order to demo the process, I'll create a CDK stack, which consists of a single S3 bucket:

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import * as s3 from 'aws-cdk-lib/aws-s3';
import * as cdk from 'aws-cdk-lib';

export class MyCdkStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props: cdk.StackProps) {
    super(scope, id, props);

    const s3Bucket = new s3.Bucket(this, 'avatars-bucket', {
      removalPolicy: cdk.RemovalPolicy.DESTROY,
    });

    // 👇 Get access to the CfnBucket resource
    const cfnBucket = s3Bucket.node.defaultChild as s3.CfnBucket;

    // 👇 Override the bucket's logical ID
    cfnBucket.overrideLogicalId('myLogicalId');
  }
}

In the code sample:

1. We defined an S3 bucket using the Level 2 Bucket construct.

2. We got access to the Level 1 CfnBucket resource and casted the type of the value to CfnBucket.

3. We overrode the logical ID of the bucket to myLogicalId

If we take a look at the synthesized CloudFormation template in the cdk.out directory, we can see that the Logical ID we've provided is reflected in the CloudFormation template:

Let's look at the Logical ID of the S3 bucket in the CloudFormation console:

We can see that the Logical ID of the bucket has been updated to the value we provided - myLogicalId.

If I were to change the logical ID of the bucket:

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-  cfnBucket.overrideLogicalId('myLogicalId');
+  cfnBucket.overrideLogicalId('anotherLogicalId');

And now run the diff command:

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npx aws-cdk diff

The output shows that if I were to run a deployment, my bucket with logical ID of myLogicalId would get deleted and a new bucket with logical ID of anotherLogicalId would get created:

We should be mindful about identifiers in CDK, especially when working with stateful resources like S3 buckets and databases. I've written an article - What is an identifier in AWS CDK if you want to read more on the topic.

# Further Reading

• AWS CDK Tutorial for Beginners - Step-by-Step Guide
• What is an identifier (id) in AWS CDK
• CDK Constructs - Complete Guide
• What is a Token in AWS CDK
• How to use Context in AWS CDK
• How to use Parameters in AWS CDK