The Amazon SDK for JavaScript V3 API
Reference Guide
Loading credentials for a Node.js Lambda function
When you create an Amazon Lambda function, you must create a special IAM role that has permission to execute the function. This role is called the execution role. When you set up a Lambda function, you must specify the IAM role you created as the corresponding execution role.
The execution role provides the Lambda function with the credentials it needs to run and to invoke other web services. As a result, you don't need to provide credentials to the Node.js code you write within a Lambda function.
For more information about creating a Lambda execution role, see Manage permissions: Using an IAM role (execution role) in the Amazon Lambda Developer Guide.