Merge pull request #187088 from raisalitch/iot-edge-limitations

IoT Edge Limitations

Author: laurabren

articles/iot-edge/TOC.yml

@@ -113,6 +113,8 @@
     href: support.md
   - name: Production deployment checklist
     href: production-checklist.md
+  - name: Limits and restrictions
+  href: iot-edge-limits-and-restrictions.md
 - name: How-to guides
   items:
   - name: Install and provision IoT Edge

articles/iot-edge/iot-edge-limits-and-restrictions.md

@@ -0,0 +1,71 @@
+---
+title: Limits and restrictions - Azure IoT Edge | Microsoft Docs 
+description: Description of the limits and restrictions when using IoT Edge.
+author: raisalitch
+ms.author: ralitchf
+ms.date: 01/28/2022
+ms.topic: conceptual
+ms.service: iot-edge
+services: iot-edge
+---
+
+# Understand Azure IoT Edge limits and restrictions
+
+[!INCLUDE [iot-edge-version-all-supported](../../includes/iot-edge-version-all-supported.md)]
+
+This article explains the limits and restrictions when using IoT Edge.
+
+## Limits
+### Number of children in gateway hierarchy
+IoT Edge gateway hierarchies have a default limit of up to 100 connected child devices. This limit can be changed by setting the **MaxConnectedClients** environment variable in the parent device's edgeHub module.
+
+For more information, see [Create a gateway hierarchy](how-to-connect-downstream-iot-edge-device.md#create-a-gateway-hierarchy).
+
+### Size of desired properties
+IoT Hub enforces the following restrictions:
+* An 8-kb size limit on the value of tags.
+* A 32-kb size limit on both the value of `properties/desired` and `properties/reported`.
+
+For more information, see [Module twin size](../iot-hub/iot-hub-devguide-module-twins.md#module-twin-size).
+
+### Number of nested hierarchy layers
+An IoT Edge device has a limit of five layers of IoT Edge devices linked as children below it.
+
+For more information, see [Parent and child relationships](iot-edge-as-gateway.md#cloud-identities).
+
+### Number of modules in a deployment
+IoT Hub has the following restrictions for IoT Edge automatic deployments:
+* 50 modules per deployment
+    * This limit is superseded by the IoT Hub 32-kb module twin size limit. For more information, see [Be mindful of twin size limits when using custom modules](production-checklist.md#be-mindful-of-twin-size-limits-when-using-custom-modules).
+* 100 deployments (including layered deployments per paid SKU hub)
+* 10 deployments per free SKU hub
+
+## Restrictions
+### Certificates
+IoT Edge certificates have the following restrictions:
+* The common name (CN) can't be the same as the "hostname" that will be used in the configuration file on the IoT Edge device.
+* The name used by clients to connect to IoT Edge can't be the same as the common name used in the edge CA certificate.
+
+For more information, see [Certificates for device security](iot-edge-certs.md#production-implications).
+
+### TPM attestation
+When using TPM attestation with the device provisioning service, you need to use TPM 2.0.
+
+For more information, see [TPM attestation device requirements](how-to-provision-devices-at-scale-linux-tpm.md#device-requirements).
+
+### Routing syntax
+IoT Edge and IoT Hub routing syntax is almost identical.
+Supported query syntax:
+* [Message routing query based on message properties](../iot-hub/iot-hub-devguide-routing-query-syntax.md#message-routing-query-based-on-message-properties)
+* [Message routing query based on message body](../iot-hub/iot-hub-devguide-routing-query-syntax.md#message-routing-query-based-on-message-body)
+
+Not supported query syntax:
+* [Message routing query based on device twin](../iot-hub/iot-hub-devguide-routing-query-syntax.md#message-routing-query-based-on-device-twin)
+
+### File upload
+IoT Hub only supports file upload APIs for device identities, not module identities. Since IoT Edge exclusively uses modules, file upload isn't natively supported in IoT Edge.
+
+For more information on uploading files with IoT Hub, see [Upload files with IoT Hub](../iot-hub/iot-hub-devguide-file-upload.md).
+
+## Next steps
+For more information, see [IoT Hub other limits](../iot-hub/iot-hub-devguide-quotas-throttling.md#other-limits).