Provision
What is a Provision
A provision is a request from Arkitekt to an app to provide an Actors for a previously registered Template by this App. Just like a Reservation, is an implicit contract between a User or a Scheduling App and Arkitekt for a Functionality, a Provision implicit contract between Arkitekt and the App for that Functionality.
Why do we need Provisions
Provisions provide a way for Arkitekt to track which Apps are currently active, accessible to other users, and which are not. If an App disconnects, or a User revokes access to this particular functionality of the App for Arkitekt, Arkitekt will mark this provision as inactive and will no longer send requests to this App for this functionality.
This becomes especially important when the App is being used in a workflow and we would like to understand if our workflow is still runnable. So how do we track this information? We use Provisions and their ability to be linked to a Reservation.
When an Workflow is reserved in Arkitekt, the scheduling app will received a provision request for this workflow, and will be expected to provide an Actor for this workflow. During its own provisioning process, the scheduling app can then "reserves" the resources it needs to run the workflow. Which will then cause provisions to be sent to the Apps that provide the resources. If now one of the Apps is not available, the signal is able to be propagated back to workflow, and the workflow can be marked as not runnable.
WHen building a workflow, you can also decide for nodes to be optional, esentially telling arkitekt that there is no need to propagate this offline signal further, as the workflow can still be run without this node.