Control unit replacement
In the Uptane framework, there are two types of control units: Primary and Secondary. A Primary control unit downloads, verifies, and distributes software to Secondaries. A Secondary control unit receives software and also verifies and installs its own metadata and images. You can find a list of Primary and Secondary control units that a device has on a page with device details. To learn more, see the related section in the Developer Guide.
Control units can be replaced offline. On device details page, on the History tab, you can find information related to their replacement. If you replace more than one Secondary control unit at the same time, the new control units replace the existing ones arbitrarily, and the device history does not display traceability between them.
Replacing control units does not influence the structure of device groups. Devices with a replaced control unit are still triggered in the same device groups as before. They also have the same device ID and list of custom device groups. After the replacement, on the page with device details, you can no longer find the old control unit, but the device history remains unchanged.