Publishing messages to IoT core using an imported lambda in greengrassv2

To publish to IoT Core from a lambda in Greengrass v2 you have 2 options.

1. https://docs.aws.amazon.com/greengrass/v2/developerguide/ipc-iot-core-mqtt.html#ipc-operation-publishtoiotcore
2. https://docs.aws.amazon.com/greengrass/v2/developerguide/legacy-subscription-router-component.html

Option 1 is the best solution.

When using option 2, you configure the legacy subscription router with the topic or topics that you want to go to the "cloud". To publish, you use the Greengrass V1 SDK's publish command.