How to configure local resource access using the Amazon Web Services Management Console

On your computer, copy the following Python script to a local file named lraTest.py. This is the app logic for the Lambda function.

# Demonstrates a simple use case of local resource access.
# This Lambda function writes a file test to a volume mounted inside
# the Lambda environment under destLRAtest. Then it reads the file and 
# publishes the content to the Amazon IoT LRAtest topic. 

import sys
import greengrasssdk
import platform
import os
import logging

# Setup logging to stdout
logger = logging.getLogger(__name__)
logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)

# Create a Greengrass Core SDK client.
client = greengrasssdk.client('iot-data')
volumePath = '/dest/LRAtest'

def function_handler(event, context):
    try:
        client.publish(topic='LRA/test', payload='Sent from Amazon IoT Greengrass Core.')
        volumeInfo = os.stat(volumePath)
        client.publish(topic='LRA/test', payload=str(volumeInfo))
        with open(volumePath + '/test', 'a') as output:
            output.write('Successfully write to a file.')
        with open(volumePath + '/test', 'r') as myfile:
            data = myfile.read()
        client.publish(topic='LRA/test', payload=data)
    except Exception as e:
        logger.error('Failed to publish message: ' + repr(e))
    return

From the Amazon IoT Greengrass Core SDK downloads page, download the Amazon IoT Greengrass Core SDK for Python to your computer.

Unzip the downloaded package to get the SDK. The SDK is the greengrasssdk folder.

Zip the following items into a file named lraTestLambda.zip:

The lraTestLambda.zip file is your Lambda function deployment package. Now you're ready to create a Lambda function and upload the deployment package.

In the Amazon Web Services Management Console, choose Services, and open the Amazon Lambda console.

Choose Functions.

Choose Create function and then choose Author from scratch.

In the Basic information section, use the following values.

1. For Function name, enter TestLRA.

2. For Runtime, choose Python 3.7.

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

Choose Create function.

Upload your Lambda function deployment package and register the handler.

1. On the Code tab, under Code source, choose Upload from. From the dropdown, choose .zip file.

   

2. Choose Upload, and then choose your lraTestLambda.zip deployment package. Then, choose Save.

3. On the Code tab for the function, under Runtime settings, choose Edit, and then enter the following values.

   • For Runtime, choose Python 3.7.

   • For Handler, enter lraTest.function_handler.

4. Choose Save.

   Note

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

Next, publish the first version of your Lambda function. Then, create an alias for the version.

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.

From Actions, choose Publish new version.

For Version description, enter First version, and then choose Publish.

On the TestLRA: 1 configuration page, from Actions, choose Create alias.

On the Create alias page, for Name, enter test. For Version, enter 1.

Choose Create.

You can now add the Lambda function to your Greengrass group.

In the Amazon IoT console navigation pane, under Manage, expand Greengrass devices, and then choose Groups (V1).

Choose the Greengrass group where you want to add the Lambda function.

On the group configuration page, choose the Lambda functions tab.

Under My Lambda functions section, choose Add.

On the Add Lambda function page, choose the Lambda function. Select TestLRA.

Choose the Lambda function version.

In the Lambda function configuration section, select System user and group and Lambda function containerization.

Next, configure the lifecycle of the Lambda function.

For Timeout, choose 30 seconds.

At the bottom of the page, choose Add Lambda function.

On the group configuration page, choose the Resources tab.

Under the Local resources section, choose Add.

On the Add a local resource page, use the following values.

1. For Resource name, enter testDirectory.

2. For Resource type, choose Volume.

3. For Local device path, enter /src/LRAtest. This path must exist on the host OS.

   The local device path is the local absolute path of the resource on the file system of the core device. This location is outside of the container that the function runs in. The path can't start with /sys.

4. For Destination path, enter /dest/LRAtest. This path must exist on the host OS.

   The destination path is the absolute path of the resource in the Lambda namespace. This location is inside the container that the function runs in.

5. Under System group owner and file access permission, select Automatically add file system permissions of the system group that owns the resource.

   The System group owner and file access permission option lets you grant additional file access permissions to the Lambda process. For more information, see Group owner file access permission.

Choose Add resource. The Resources page displays the new testDirectory resource.

On the group configuration page, choose the Subscriptions tab.

Choose Add.

On the Create a subscription page, configure the source and target, as follows:

1. For Source type, choose Lambda function, and then choose TestLRA.

2. For Target type, choose Service, and then choose IoT Cloud.

3. For Topic filter, enter LRA/test, and then choose Create subscription.

The Subscriptions page displays the new subscription.

Next, configure a subscription that invokes the function from Amazon IoT.

On the Subscriptions page, choose Add Subscription.

On the Select your source and target page, configure the source and target, as follows:

1. For Source type, choose Lambda function, and then choose IoT Cloud.

2. For Target type, choose Service, and then choose TestLRA.

3. Choose Next.

On the Filter your data with a topic page, for Topic filter, enter invoke/LRAFunction, and then choose Next.

Choose Finish. The Subscriptions page displays both subscriptions.

Make sure that the Amazon IoT Greengrass core is running. Run the following commands in your Raspberry Pi terminal, as needed.

1. To check whether the daemon is running:

   ps aux | grep -E 'greengrass.*daemon'

   If the output contains a root entry for /greengrass/ggc/packages/1.11.6/bin/daemon, then the daemon is running.

   Note

   The version in the path depends on the Amazon IoT Greengrass Core software version that's installed on your core device.

2. To start the daemon:

   cd /greengrass/ggc/core/
   sudo ./greengrassd start

On the group configuration page, choose Deploy.

If prompted, on the Lambda function tab, under System Lambda functions, select IP detector, and then Edit, and then Automatically detect.

This enables devices to automatically acquire connectivity information for the core, such as IP address, DNS, and port number. Automatic detection is recommended, but Amazon IoT Greengrass also supports manually specified endpoints. You're only prompted for the discovery method the first time that the group is deployed.

The Deployments page shows the deployment timestamp, version ID, and status. When completed, the deployment status is Completed.

For troubleshooting help, see Troubleshooting Amazon IoT Greengrass.

From the Amazon IoT console navigation menu, under Test, choose MQTT test client.

Under Subscribe to a topic, for Topic filter, enter LRA/test.

Under Additional information, for MQTT payload display, select Display payloads as strings.

Choose Subscribe. Your Lambda function publishes to the LRA/test topic.

Under Publish to a topic, in the Topic nameenter invoke/LRAFunction, and then choose Publish to invoke your Lambda function. The test is successful if the page displays the function's three message payloads.