AWS Documentation » AWS IoT Greengrass » Developer Guide » Getting Started with AWS IoT Greengrass » Module 6: Accessing Other AWS Services » Create and Configure the Lambda Function

Create and Configure the Lambda Function

In this step, you create a Lambda function that tracks the number of cars that pass the traffic light. Every time that the GG_TrafficLight shadow state changes to G, the Lambda function simulates the passing of a random number of cars (from 1 to 20). On every third G light change, the Lambda function sends basic statistics, such as min and max, to a DynamoDB table.

1. On your computer, create a folder named car_aggregator.

2. From the AWS IoT Greengrass samples repository on GitHub, download the carAggregator.py function to the car_aggregator folder.

3. Run the following command in a command-line window to install the boto3 (AWS SDK for Python) package and its dependencies in the car_aggregator folder. (For Windows, use an elevated command prompt.)

   pip install boto3 -t path-to-car_aggregator-folder

   This results in a directory listing similar to the following:

   

   Greengrass Lambda functions use the AWS SDK to access other AWS services. For more information, see Boto 3 - The AWS SDK for Python.

4. Compress the contents of the car_aggregator folder into a .zip file named car_aggregator.zip. (Compress the folder's contents, not the folder.) This is your Lambda function deployment package.

5. In the Lambda console, create a function named GG_Car_Aggregator, and set the remaining fields as follows:

   • For Runtime, choose Python 2.7.

   • For Role, choose Choose an existing role.

   • For Existing role, choose Lambda_DynamoDB_Role.

   Choose Create function.

   

6. Upload your Lambda function deployment package:

   1. On the Configuration tab, under Function code, set the following fields:

      • For Code entry type, choose Upload a .zip file.

      • For Runtime, choose Python 2.7.

      • For Handler, enter carAggregator.function_handler

   2. Choose Upload, and then choose car_aggregator.zip.

   3. Choose Save.

      

7. Publish the Lambda function, and then create an alias named GG_CarAggregator. For step-by-step instructions, see the steps to publish the Lambda function and create an alias in Module 3 (Part 1).

8. In the AWS IoT Core console, add the Lambda function that you just created to your AWS IoT Greengrass group:

   1. On the group configuration page, choose Lambdas, and then choose Add Lambda.

   2. Choose Use existing Lambda.

      

   3. Choose GG_Car_Aggregator, and then choose Next.

      

   4. Choose Alias: GG_CarAggregator, and then choose Finish.

      

   Note

   You can remove other Lambda functions from earlier modules.

9. Edit the Lambda function configuration:

   1. Choose the ellipsis (…) associated with the Lambda function, and then choose Edit Configuration.

      

   2. Under Lambda lifecycle, choose Make this function long-lived and keep it running indefinitely, and then choose Update.