TITLE FOR BUG REPORT

[jfrabell]

Checkboxes for prior research

• I've gone through Developer Guide and API reference
• I've checked AWS Forums and StackOverflow.
• I've searched for previous similar issues and didn't find any solution.

Describe the bug

CognitoIdentityServiceProviderClient is not a constructor in Lambda Node.js 20 runtime

Regression Issue

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

SDK version number

@aws-sdk/client-cognito-identity-provider: 3.585.0 and 3.556.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

nodejs20.x

Reproduction Steps

The most minimal reproduction steps use the AWS CLI directly, bypassing all frameworks:

1. Create a folder and run npm init -y.
2. Run npm install @aws-sdk/client-cognito-identity-provider.
3. Create an index.js file with the following code:

exports.handler = async (event) => {
    // This line throws the error
    const client = new CognitoIdentityServiceProviderClient({ region: 'us-east-2' });
    console.log("Client instantiated successfully.");
};

4. Package the function: zip -r function.zip index.js node_modules
5. Deploy using the AWS CLI: aws lambda create-function --function-name bug-repro-test
6. Invoke the function.

Observed Behavior

The function fails with a TypeError: CognitoIdentityServiceProviderClient is not a constructor. Diagnostic logging shows that the property on the required module is undefined.

Expected Behavior

The Lambda function should execute successfully, and the CognitoIdentityServiceProviderClient should be a valid constructor.

Possible Solution

No response

Additional Information/Context

This issue was troubleshooted for over 20 man hours. We confirmed the bug persists across:

• Serverless Framework v4 (with native and serverless-esbuild bundlers).
• Lambda Layers deployment.
• Different module formats (.js with "type": "module", .cjs).
• Multiple versions of the SDK.

The only successful workaround was to abandon the v3 SDK entirely and use the v2 aws-sdk package.