Azure IoT Hub provides the capability to stream data from your connected devices and integrate that data into your business applications. IoT Hub offers two methods for integrating IoT events into other Azure services or business applications. This article discusses the two features that provide this capability, so that you can choose which option is best for your scenario.
Note
Some of the features mentioned in this article, like cloud-to-device messaging, device twins, and device management, are only available in the standard tier of IoT Hub. For more information about the basic and standard/free IoT Hub tiers, see Choose the right IoT Hub tier and size for your solution.
IoT Hub message routing: This IoT Hub feature enables users to route device-to-cloud messages to service endpoints like Azure Storage containers, Event Hubs, Service Bus queues, and Service Bus topics. Routing also provides a querying capability to filter the data before routing it to the endpoints. In addition to device telemetry data, you can also route non-telemetry events and use them to trigger actions.
IoT Hub integration with Event Grid: Azure Event Grid is a fully managed event routing service that uses a publish-subscribe model. IoT Hub and Event Grid work together to integrate IoT Hub events into Azure and non-Azure services, in near-real time. IoT Hub publishes both device events and telemetry events.
DifferencesWhile both message routing and Event Grid enable alert configuration, there are some key differences between the two. Refer to the following table for details:
Feature IoT Hub message routing IoT Hub integration with Event Grid Device messages and events Yes, message routing supports telemetry data, device twin changes, device lifecycle events, digital twin change events, and device connection state events. Yes, Event Grid supports telemetry data and device events like device created/deleted/connected/disconnected. But Event Grid doesn't support device twin change events and digital twin change events. Ordering Yes, message routing maintains the order of events. No, Event Grid doesn't guarantee the order of events. Filtering Rich filtering on message application properties, message system properties, message body, device twin tags, and device twin properties. Filtering isn't applied to digital twin change events. For examples, see Message Routing Query Syntax. Filtering based on event type, subject type and attributes in each event. For examples, see Understand filtering events in Event Grid Subscriptions. When subscribing to telemetry events, you can apply filters on the data to filter on message properties, message body and device twin in your IoT Hub, before publishing to Event Grid. See how to filter events. EndpointsIoT Hub message routing and Event Grid have similarities too, some of which are detailed in the following table:
Feature IoT Hub message routing IoT Hub integration with Event Grid Maximum message size 256 KB, device-to-cloud 256 KB, device-to-cloud Reliability High: Delivers each message to the endpoint at least once for each route. Expires all messages that aren't delivered within one hour. High: Delivers each message to the webhook at least once for each subscription. Expires all events that aren't delivered within 24 hours. Scalability High: Optimized to support millions of simultaneously connected devices sending billions of messages. High: Capable of routing 10,000,000 events per second per region. Latency Low: Near-real time. Low: Near-real time. Send to multiple endpoints Yes, send a single message to multiple endpoints. Yes, send a single message to multiple endpoints. Security IoT Hub provides per-device identity and revocable access control. For more information, see the IoT Hub access control. Event Grid provides validation at three points: event subscriptions, event publishing, and webhook event delivery. For more information, see Event Grid security and authentication. How to chooseIoT Hub message routing and the IoT Hub integration with Event Grid perform different actions to achieve similar results. They both take information from your IoT Hub solution and pass it on so that other services can react. So how do you decide which one to use? Consider the following questions to help guide your decision:
What kind of data are you sending to the endpoints?
Use IoT Hub message routing when you have to send telemetry data to other services. Message routing also enables querying message application and system properties, message body, device twin tags, and device twin properties.
The IoT Hub integration with Event Grid works with events that occur in the IoT Hub service. These IoT Hub events include telemetry data, device created, deleted, connected, and disconnected. When subscribing to telemetry events, you can apply additional filters on the data to filter on message properties, message body and device twin in your IoT Hub, before publishing to Event Grid. See how to filter events.
What endpoints need to receive this information?
IoT Hub message routing supports limited number of unique endpoints and endpoint types, but you can build connectors to reroute the data and events to additional endpoints. For a complete list of supported endpoints, see the table in the previous section.
The IoT Hub integration with Event Grid supports 500 endpoints per IoT Hub and a larger variety of endpoint types. It natively integrates with Azure Functions, Logic Apps, Storage and Service Bus queues, and also works with webhooks to extend sending data outside of the Azure service ecosystem and into third-party business applications.
Does it matter if your data arrives in order?
IoT Hub message routing maintains the order in which messages are sent, so that they arrive in the same way.
Event Grid does not guarantee that endpoints receive events in the same order that they occurred. For those cases in which absolute order of messages is significant and/or in which a consumer needs a trustworthy unique identifier for messages, we recommend using message routing.
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