Dynamic Deployment

This page describes how the dynamic deployment of processes works. The main idea is that the Distributed Process Engines (DPE) decide at runtime if the next activity is executed on the same DPE or if it should be sent to another engine.

For deciding where to execute the next process step, there are multiple execution constraints to consider. An important criteria are the needed capabilities for the next task. A capability is a specific function a machine offers. For example, if a temperature sensor is connected to an IoT device, the process engine running on that device can offer this capability to other engines. Other decision criterias can be constraints like the engines workload and performance.

Step 1: Discover or add Capabilities in the Management System

The Management System can automatically discover all capabilities in the connected network. They are then displayed on the "Capability View". Since at runtime a process can travel outside the network scope, there is the possibility to add manually more capabilities.

Step 2: Reuse the Capabilities in the Process

Currently it is only possible to use the capabilities as function calls inside a Script Task
The used capabilities are added to the BPMN XML via BPMN extensions of PROCEED

XML

<bpmn2:scriptTask id="Task_1pdn5o1" scriptFormat="javascript">
    <bpmn2:script>
        <![CDATA[
        let a = services.system.capability.startTask( "takePhoto" );
        next();
        ]]>
    </bpmn2:script>
    <bpmn2:extensionElements>
        <proceed:capabilities>
            <proceed:capability>takePhoto</proceed:capability>
        </proceed:capabilities>
    </bpmn2:extensionElements>
</bpmn2:scriptTask>

Step 3: Deploy the complete process to a suitable DPE

The complete, unseparated process is deployed to a Distributed Process Engines in the connected network which offers the needed capability to execute the first activity
It is possible that the first activity does not need any special capability -- just pure BPMN execution
Theoretically it is also possible the deploy the process to an engine that does not offer the needed capability. Since this engine can (at a later time) be connected to other networks not reachable for the Management System the engine then serves as a proxy.

Step 4: The DPE executes the process step by step and decides if to retransfer the process

The Process Manager executes the BPMN process step by step
After each step it evaluates if the next activity can and should be executed on the same machine
- If it should be not executed on the same machine, the DPE sends the complete process to the next DPE that can execute it
- The selection of the next process engine is currently a simple process: the first machine that is capable of running the next step is picked. If there is no machine available the process waits until one system becomes available (This can lead to a deadlock situation.)
  - At a later stage it is inteded to extend the selection process with more variables and smarter decision making.
- Afterwards it starts the process on the next engine by sending it the id of the next task to start

PROCEED Engine Architecture Overview

Step 5: Repeat Step 4 until the end of the Process is reached

Deployment and Execution Capability Description