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Custom Fragments

thin-edge.io supports update custom fragments (also known as properties) on the device's digital twin representation in Cumulocity IoT.

Default fragments​

By default, the device will send the following information to Cumulocity IoT. The information makes it easy to identify devices which are using thin-edge.io in your fleet.

{
  "type": "thin-edge.io",
  "c8y_Agent": {
    "name": "thin-edge.io",
    "url": "https://thin-edge.io",
    "version": "1.0.0"
  }
}

The default value for the type property can be changed using the tedge config command as follows:

sudo tedge config set device.type VALUE

For example, you can set the type property to edge_gateway using:

sudo tedge config set device.type edge_gateway

Custom fragments​

Additional fragments can be added to the device by either publishing to a give MQTT topic, or via a file based method. Each section describes what data and when to use it.

MQTT Dynamic Fragments​

thin-edge.io offers an MQTT topic which can be used to publish data to custom fragments for a device, child devices or services.

  • Values which change over time
  • Update values without having to restart any services

The following shows an example of publishing the name and version of the Operating System to the os_Version fragment for the main device.

tedge mqtt pub 'te/device/main///twin/os_Version' '{
  "name": "Poky (Yocto Project Reference Distro)",
  "version": "4.0.15 (kirkstone)"
}'

The example above will result in the following fragment being added to the device's digital twin (e.g. Managed Object) in Cumulocity IoT.

{
  // ... other fragments are left out for simplicity
  "os_Version": {
    "name": "Poky (Yocto Project Reference Distro)",
    "version": "4.0.15 (kirkstone)"
  }
}

File-based Static Fragments​

The file based approach is intended for static information, e.g. build date, or a custom image type assigned to the device. The values are only published on startup of the tedge-mapper-c8y service.

If you wish to add more fragments to Cumulocity, you can do so by populating /etc/tedge/device/inventory.json.

An example inventory.json looks something like this:

file: /etc/tedge/device/inventory.json
{
  "c8y_RequiredAvailability": {
    "responseInterval": 5
  },
  "c8y_Hardware": {
    "model": "BCM2708",
    "revision": "000e",
    "serialNumber": "00000000e2f5ad4d"
  }
}

To see the changes you need to restart the tedge-mapper. If you're using systemctl you can do:

sudo systemctl restart tedge-mapper-c8y

In the Cumulocity UI this will looks something like this:

Cumulocity custom fragments

For information on which fragments Cumulocity supports please see the Cumulocity API docs.