Sending Events

Events on thin-edge.io can be used to trigger signals when some event happens in the system. For example, a person entering a room or someone logging into a machine/website can all be represented as events. Events are stateless and hence are processed as and when they occur. They don't represent state but can be used to represent state changes. An event can't be updated/cleared once its triggered, unlike alarms that are cleared explicitly after processing.

Every event is uniquely identified by its type. If multiple events are raised for a given type, thin-edge.io will process them all separately in the order in which they were raised.

Sending an event

An event can be triggered on thin-edge.io by sending an MQTT message in thin-edge.io JSON format to certain MQTT topics.

The scheme of the topic to publish the event data is as follows:

Topic

te/+/+/+/+/e/<event-type>

The payload format must be as follows:

Payload

{
  "text": "<event text>",
  "time": "<Timestamp in ISO-8601 format>"
}

Here is a sample event triggered for a login_event event type:

tedge

tedge mqtt pub 'te/device/main///e/login_event' '{
  "text": "A user just logged in"
}'

mosquitto

mosquitto_pub -t 'te/device/main///e/login_event' -m '{
  "text": "A user just logged in"
}'

mqtt

Publish topic

te/device/main///e/login_event

Payload

{
  "text": "A user just logged in"
}

note

Both the text field and the time field are optional.

When the text field is not provided, the event-type from the MQTT topic will be used as the message as well if the connected cloud mandates one. When the time field is not provided, thin-edge.io will use the current system time as the time of the event. When you want to skip both fields, use an empty payload to indicate the same. There are no such restrictions on the <event-type> value.

Sending events from child devices

Events for child devices can be sent by publishing the event payload to te/device/<child-device-id>///e/<event-type> topic, where the child-device-id is the unique device id of the child device. The event payload structure is the same, as described in the previous section.

Cloud data mapping

If the device is connected to some supported IoT cloud platform, an event that is triggered locally on thin-edge.io will be forwarded to the connected cloud platform as well. The mapping of thin-edge.io events data to its respective cloud-native representation will be done by the corresponding cloud mapper process. For example, if the device is connected to Cumulocity IoT cloud platform, the Cumulocity cloud mapper process will translate the thin-edge.io event JSON data to its equivalent Cumulocity SmartREST representation.

caution

As of now, event data mapping is supported only on Cumulocity IoT cloud platform.

Cumulocity cloud data mapping

The Cumulocity mapper will convert thin-edge.io JSON events into its Cumulocity SmartREST equivalent if the payload only contains either a text field or time field.

For example the login_event described in the earlier sections will be converted to the following Cumulocity SmartREST message:

400,login_event,"A user just logged in",2021-01-01T05:30:45+00:00

The message is published to the c8y/s/us topic which will get forwarded to the connected Cumulocity cloud instance.

If the event JSON payload contains fields other than text and time, or when the payload size is more than 16K irrespective of its contents, it will be converted to Cumulocity JSON format.

The Cumulocity JSON mapping of the same event would be as follows:

{
  "type":"login_event",
  "text":"A user just logged in",
  "time":"2021-01-01T05:30:45+00:00",
  "externalSource":{
    "externalId":"<child-device-id>",
    "type":"c8y_Serial"
  }
}

note

Mapped events will be sent to Cumulocity via MQTT if the incoming thin-edge.io JSON event payload size is less than 16K bytes. If higher, HTTP will be used.

Find more information about events data model in Cumulocity here.

Sending an event for a child/external device to the cloud

An event for a child/external device can be triggered on thin-edge.io by sending an MQTT message in thin-edge.io JSON format to certain MQTT topics.

The scheme of the topic to publish the event data is as follows:

Topic

te/device/<child-device-id>///e/<event-type>

The payload format must be as follows:

Payload

{
  "text": "<event text>",
  "time": "<Timestamp in ISO-8601 format>"
}

Here is a sample event triggered for a login_event event type for the external_sensor child device:

Command to send the event from a external device as below:

tedge

tedge mqtt pub 'te/device/external_sensor///e/login_event' '{
  "text": "A user just logged in"
}'

mosquitto

mosquitto_pub -t 'te/device/external_sensor///e/login_event' -m '{
  "text": "A user just logged in"
}'

mqtt

Publish topic

te/device/external_sensor///e/login_event

Payload

{
  "text": "A user just logged in"
}

Mapping of events to cloud-specific data format

If the child/external device is connected to some supported IoT cloud platform, an event that is triggered locally on thin-edge.io will be forwarded to the connected cloud platform as well. The mapping of thin-edge.io events data to its respective cloud-native representation will be done by the corresponding cloud mapper process.

Cumulocity cloud data mapping

The Cumulocity mapper will convert thin-edge.io JSON events into its Cumulocity JSON equivalent and sends them to the Cumulocity cloud.

The translated payload will be in the below format.

{
  "type": "login_event",
  "text": "A user just logged in",
  "time": "2021-01-01T05:30:45+00:00",
  "externalSource":{
    "externalId": "external_sensor",
    "type": "c8y_Serial"
  }
}

Here the externalId will be derived from the child-device-id of the child device event topic.