IoT Hub data connection

Azure IoT Hub is a managed service, hosted in the cloud, that acts as a central message hub for bi-directional communication between your IoT application and the devices it manages. Azure Data Explorer offers continuous ingestion from customer-managed IoT Hubs, using its Event Hub compatible built in endpoint.

The IoT ingestion pipeline goes through several steps. First, you create an IoT Hub, and register a device to it. You then create a target table in Azure Data Explorer into which the data in a particular format, will be ingested using the given ingestion properties. The Iot Hub connection needs to know events routing to connect to the Azure Data Explorer table. Data is embedded with selected properties according to the event system properties mapping. This process can be managed through the Azure portal, programmatically with C# or Python, or with the Azure Resource Manager template.

For general information about data ingestion in Azure Data Explorer, see Azure Data Explorer data ingestion overview.

Data format

  • Data is read from the Event Hub endpoint in form of EventData objects.
  • See supported formats.

    Note

    IoT Hub doesn't support the .raw format.

  • See supported compressions.
    • The original uncompressed data size should be part of the blob metadata, or else Azure Data Explorer will estimate it. The ingestion uncompressed size limit per file is 4 GB.

Ingestion properties

Ingestion properties instruct the ingestion process where to route the data and how to process it. You can specify Ingestion properties of the events using the EventData.Properties. You can set the following properties:

Property Description
Database Name (case sensitive) of the target database. This property can be used if you want to send the data to a different database than the database the data connection was created on (the default database). To route the data to multiple databases, you must first set up the connection as a multi-database connection. For more information, see Events routing.
Table Name (case sensitive) of the existing target table. Overrides the Table set on the Data Connection pane.
Format Data format. Overrides the Data format set on the Data Connection pane.
IngestionMappingReference Name of the existing ingestion mapping to be used. Overrides the Column mapping set on the Data Connection pane.
Encoding Data encoding, the default is UTF8. Can be any of .NET supported encodings.

Note

Only events enqueued after you create the data connection are ingested.

Events routing

When you create a data connection to your cluster, you specify the routing for where to send ingested data. The default routing is to the target table specified in the connection string that is associated with the target database. The default routing for your data is also referred to as static routing. You can specify an alternative routing for your data by using the event data properties.

Route event data to an alternate database

Routing data to an alternate database is off by default. To send the data to a different database, you must first set the connection as a multi-database connection. You can do this in the Azure portal Azure portal, C#, Python, or an ARM template. The user, group, service principal, or managed identity used to allow database routing must at least have the contributor role and write permissions on the cluster.

To specify an alternate database, set the Database ingestion property.

Warning

Specifying an alternate database without setting the connection as a multi-database data connection will cause the ingestion to fail.

Route event data to an alternate table

You can also specify target table properties for each event, using event properties. The connection will dynamically route the data as specified in the EventData.Properties, overriding the static properties for this event. To specify an alternate table, set the Table ingestion property.

Note

If My data includes routing info selected, you must provide the necessary routing information as part of the events properties.

Event system properties mapping

System properties are a collection used to store properties that are set by the IoT Hub service, on the time the event is received. The Azure Data Explorer IoT Hub connection will embed the selected properties in the data landing in your table.

Note

For csv mapping, properties are added at the beginning of the record in the order listed in the table below. For json mapping, properties are added according to property names in the following table.

System properties

IoT Hub exposes the following system properties:

Property Description
message-id A user-settable identifier for the message used for request-reply patterns.
sequence-number A number (unique per device-queue) assigned by IoT Hub to each cloud-to-device message.
to A destination specified in Cloud-to-Device messages.
absolute-expiry-time Date and time of message expiration.
iothub-enqueuedtime Date and time the Device-to-Cloud message was received by IoT Hub.
correlation-id A string property in a response message that typically contains the MessageId of the request, in request-reply patterns.
user-id An ID used to specify the origin of messages.
iothub-ack A feedback message generator.
iothub-connection-device-id An ID set by IoT Hub on device-to-cloud messages. It contains the deviceId of the device that sent the message.
iothub-connection-auth-generation-id An ID set by IoT Hub on device-to-cloud messages. It contains the connectionDeviceGenerationId (as per Device identity properties) of the device that sent the message.
iothub-connection-auth-method An authentication method set by IoT Hub on device-to-cloud messages. This property contains information about the authentication method used to authenticate the device sending the message.
iothub-creation-time-utc Timestamp recording when the message was sent by the device.

If you selected Event system properties in the Data Source section of the table, you must include the properties in the table schema and mapping.

Schema mapping examples

Table schema mapping example

If your data includes three columns (Timespan, Metric, and Value) and the properties you include are iothub-connection-device-id and sequence-number, create or alter the table schema by using this command:

    .create-merge table TestTable (TimeStamp: datetime, Metric: string, Value: int, IotHubDeviceId:long, IotHubSequenceNumber:long)

CSV mapping example

Run the following commands to add data to the beginning of the record. Note ordinal values.

    .create table TestTable ingestion csv mapping "CsvMapping1"
    '['
    '   { "column" : "Timespan", "Properties":{"Ordinal":"2"}},'
    '   { "column" : "Metric", "Properties":{"Ordinal":"3"}},'
    '   { "column" : "Value", "Properties":{"Ordinal":"4"}},'
    '   { "column" : "IotHubDeviceId", "Properties":{"Ordinal":"0"}},'
    '   { "column" : "IotHubSequenceNumber", "Properties":{"Ordinal":"1"}}'
    ']'

JSON mapping example

Data is added by using the system properties mapping. Run these commands:

    .create table TestTable ingestion json mapping "JsonMapping1"
    '['
    '    { "column" : "Timespan", "Properties":{"Path":"$.timestamp"}},'
    '    { "column" : "Metric", "Properties":{"Path":"$.metric"}},'
    '    { "column" : "Value", "Properties":{"Path":"$.metric_value"}},'
    '    { "column" : "IotHubDeviceId", "Properties":{"Path":"$.iothub-connection-device-id"}},'
    '    { "column" : "IotHubSequenceNumber", "Properties":{"Path":"$.sequence-number"}}'
    ']'

Event user properties mapping

There is no support for enriching the IoT Hub events payload with user properties. Consider embedding user properties in the event body upstream.

IoT Hub connection

Note

For best performance, create all resources in the same region as the Azure Data Explorer cluster.

Create an IoT Hub

If you don't already have one, Create an Iot Hub. Connection to IoT Hub can be managed through the Azure portal, programmatically with C# or Python, or with the Azure Resource Manager template.

Note

  • The device-to-cloud partitions count is not changeable, so you should consider long-term scale when setting partition count.
  • Consumer group must be unique per consumer. Create a consumer group dedicated to Azure Data Explorer connection. Find your resource in the Azure portal and go to Built-in endpoints to add a new consumer group.
  • The Data Connection uses IoT Hub Built-in endpoint. If you configure any other Message routing endpoint, messages stop flowing to the Built-in endpoint unless a route is created to that endpoint. To ensure messages continues to flow to the built-in-endpoint if a new route is added, configure a route to the events endpoint. For more information, see IoT Hub Troubleshooting Message Routing.

Sending events

See the sample project that simulates a device and generates data.

Next steps

There are various methods to ingest data into IoT Hub. See the following links for walkthroughs of each method.