The hawkBit [update server](management-api) provides REST resources which are consumed by the device to retrieve software update tasks.
This API is based on HTTP standards and a polling mechanism.
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> ℹ️ **Note**: In DDI the target is identified using a **controllerId**.
> Controller is used as a term for the actual service/client on the device.
> That allows users to have in some cases even multiple clients on the same target for different tasks, e.g. Firmware update and App management.
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### State Machine Mapping
For historical reasons the DDI has a different state machine and status messages than the [Target State Machine](targetstate) of the hawkBit update server.
This is kept in order to ensure that *DDI* stays compatible for devices out there in the field.
A future version “2” of *DDI* might change that.
*DDI* also defines more states than the update server, e.g. multiple DDI states are currently mapped by the *DDI* implementation to **RUNNING** state.
It is possible that in the future hawkBit will fully leverage these additional states.
The *DDI* API allows the device to provide the following feedback messages:
| CANCELED | This is sent by the target as confirmation of a cancellation request by the update server. | CANCELED |
| REJECTED | This is sent by the target in case an update or cancellation is rejected, i.e. cannot be fulfilled at this point in time. Note: the target should send a CLOSED→ERROR if it believes it will not be able to proceed the action at all. | WARNING |
| CLOSED | Target completes the action either with [`status.result.finished`](../status-result-finished.md) SUCCESS or FAILURE as result. Note: DDI defines also a status NONE which will not be interpreted by the update server and handled like SUCCESS. | **ERROR** (DDI FAILURE) or **FINISHED** (DDI SUCCESS or NONE) |
| DOWNLOAD | This can be used by the target to inform that it is downloading artifacts of the action. | DOWNLOAD |
| DOWNLOADED | This can be used by the target to inform that it has downloaded artifacts of the action. | DOWNLOADED |
| PROCEEDING | This can be used by the target to inform that it is working on the action. | RUNNING |
| SCHEDULED | This can be used by the target to inform that it scheduled the action. | RUNNING |
| RESUMED | This can be used by the target to inform that it continued to work on the action. | RUNNING |
