End of support notice: On October 7th, 2026, Amazon will discontinue support for Amazon IoT Greengrass Version 1. After October 7th, 2026, you will no longer be able to access the Amazon IoT Greengrass V1 resources. For more information, please visit [Migrate from Amazon IoT Greengrass Version 1](https://docs.amazonaws.cn/greengrass/v2/developerguide/migrate-from-v1.html).

# Module 4: Interacting with client devices in an Amazon IoT Greengrass group
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This module shows you how local IoT devices, called *client devices* or *devices*, can connect to and communicate with an Amazon IoT Greengrass core device. Client devices that connect to an Amazon IoT Greengrass core are part of an Amazon IoT Greengrass group and can participate in the Amazon IoT Greengrass programming paradigm. In this module, one client device sends a Hello World message to another client device in the Greengrass group.

![\[Amazon IoT connected to an Amazon IoT Greengrass core, which is connected to client device #1 and client device #2.\]](http://docs.amazonaws.cn/en_us/greengrass/v1/developerguide/images/gg-get-started-065.5.png)


Before you begin, run the [Greengrass device setup](quick-start.md) script or complete [Module 1](module1.md) and [Module 2](module2.md). This module creates two simulated client devices. You do not need other components or devices.

This module should take less than 30 minutes to complete.

**Topics**
+ [Create client devices in an Amazon IoT Greengrass group](device-group.md)
+ [Configure subscriptions](config-subs.md)
+ [Install the Amazon IoT Device SDK for Python](IoT-SDK.md)
+ [Test communications](test-comms.md)