AWS IoT Greengrass
Developer Guide

Create and Package a Lambda Function

To run on an AWS IoT Greengrass core, a Python Lambda function requires the AWS IoT Greengrass Core SDK for Python. For this tutorial, you include the greengrasssdk folder in the Lambda function deployment package.

Note

If you're running Python Lambda functions, you can also use pip to install the AWS IoT Greengrass Core SDK for Python on the core device. Then you can deploy your functions without including the SDK in the Lambda function deployment package. For more information, see greengrasssdk.

In this section, you:

  • Download the AWS IoT Greengrass Core SDK for Python to your computer (not the AWS IoT Greengrass core device). For this tutorial, you download the SDK on GitHub from the AWS IoT Greengrass Core SDK downloads page.

  • Get the Python Lambda function (named greengrassHelloWorld.py) from the downloaded SDK.

  • Create a Lambda function deployment package named hello_world_python_lambda.zip that contains greengrassHelloWorld.py and the greengrasssdk folder.

  • Use the Lambda console to upload the hello_world_python_lambda.zip package.

  • Use the AWS IoT Core console to transfer the package to the AWS IoT Greengrass core device (during group deployment).

  1. Download the AWS IoT Greengrass Core SDK for Python from the AWS IoT Greengrass Core SDK downloads page. In the Python section, choose v1.4.0 - Current version (on GitHub) and then download the SDK.

  2. Unzip the downloaded package to get the Lambda function code and the SDK.

    The Lambda function in this module uses:

    • The greengrassHelloWorld.py file in examples\HelloWorld. This is your Lambda function code.

    • The greengrasssdk folder. This is the SDK.

    The following code is from greengrassHelloWorld.py. (To save space, all code comments have been removed.) Note that every five seconds, the function publishes one of two possible messages to the hello/world topic.

    import greengrasssdk import platform from threading import Timer import time client = greengrasssdk.client('iot-data') my_platform = platform.platform() def greengrass_hello_world_run(): if not my_platform: client.publish(topic='hello/world', payload='Hello world! Sent from Greengrass Core.') else: client.publish(topic='hello/world', payload='Hello world! Sent from Greengrass Core running on platform: {}'.format(my_platform)) Timer(5, greengrass_hello_world_run).start() greengrass_hello_world_run() def function_handler(event, context): return
  3. Copy greengrasssdk to the HelloWorld folder that contains greengrassHelloWorld.py.

  4. To create the Lambda function deployment package, save the greengrassHelloWorld.py file and the greengrasssdk folder to a compressed .zip file named hello_world_python_lambda.zip. The .py file and SDK folder must be in the root of the directory.

    
                            Screenshot showing zipped contents of
                                hello_word_python_lambda.zip.

    For UNIX-like systems (including the Mac terminal), you can use the following command to package the file and folder:

    sudo zip -r hello_world_python_lambda.zip greengrasssdk greengrassHelloWorld.py

    Note

    Depending on your distribution, you might need to install zip first (for example, by running sudo apt-get install zip). The installation command for your distribution might be different.

    Now you're ready to create your Lambda function and upload the deployment package.

  5. Open the Lambda console and choose Create function.

  6. Choose Author from scratch.

  7. Name your function Greengrass_HelloWorld, and set the remaining fields as follows:

    • For Runtime, choose Python 2.7.

    • For Permissions, keep the default setting. This creates an execution role that grants basic Lambda permissions. This role isn't used by AWS IoT Greengrass.

    Choose Create function.

    
                            The "Basic information" section with the "Function name" field set to
                                "Greengrass_HelloWorld" and the "Runtime" field set to "Python 2.7".
  8. 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 greengrassHelloWorld.function_handler

    2. Choose Upload, and then choose hello_world_python_lambda.zip. (The size of your hello_world_python_lambda.zip file might be different from what's shown here.)

      
                                    Screenshot of the Configuration tab with Upload a .zip
                                        file, Python 2.7, greengrassHelloWorld.function_handler, and
                                        Upload highlighted.
    3. Choose Save.

      
                                    Screenshot with the Save button highlighted.

      Note

      The Test button on the AWS Lambda console doesn't work with this function. The AWS IoT Greengrass Core SDK doesn't contain modules that are required to run your Greengrass Lambda functions independently in the AWS Lambda console. These modules (for example, greengrass_common) are supplied to the functions after they are deployed to your Greengrass core.

      Tip

      To see your uploaded code, from Code entry type, choose Edit code inline.

  9. Publish the Lambda function:

    1. From Actions, choose Publish new version.

      
                                    Screenshot of the Actions menu with Publish new version
                                        highlighted.
    2. For Version description, enter First version, and then choose Publish.

      
                            Screenshot with the Version description field set to First
                                version and the Publish button highlighted.
  10. Create an alias for the Lambda function version:

    Note

    Greengrass groups can reference a Lambda function by alias (recommended) or by version. Using an alias makes it easier to manage code updates because you don't have to change your subscription table or group definition when the function code is updated. Instead, you just point the alias to the new function version.

    1. From Actions, choose Create alias.

      
                            Screenshot of the Actions menu set to Create alias.
    2. Name the alias GG_HelloWorld, set the version to 1 (which corresponds to the version that you just published), and then choose Create.

      Note

      AWS IoT Greengrass doesn't support Lambda aliases for $LATEST versions.

       

      
                            Screenshot of Create a new alias with the Name field set to
                                GG_HelloWorld, the Version field set to 1, and the Create button
                                highlighted.