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The workflow engine is the core of the orchestrator, it is responsible for the following functions:

  • Safely and reliable manipulate customer Subscriptions from one state to the next and maintain auditability.
  • Create an API through which Subscriptions can be manipulated programmatically.
  • Execute step functions in order and allow the retry of previously failed process-steps in an idempotent way.
  • Atomically execute workflow functions.

Best Practices

The orchestrator will always attempt to be a robust a possible when executing workflow steps. However it is always up to the developer to implement the best practices as well as he/she can.

Safeguards in the orchestrator;

  • Steps will be treated as atomic units: All code must execute otherwise the state will not be commited to the database. For this reason it is not possible to call .commit() on the ORM within a step function
  • Workflows are only allowed to be run on insync subscriptions, unless explicitly configured otherwise. This is to safeguard against resource contention. One of the first things a workflow should do is set the subscription it it manipulating out of sync. No other workflow can then manipulate it.
  • Failed steps can be retried again and again, they use the state from the last successful step as their starting point.

Coding gotchas

  • The orchestrator is best suited to be used as a data manipulator, not as a data transporter. Use the State log as a log of work, not a log of data. If the data you enter in the state is corrupt or wrong, you might need to attempt a very difficult database query to update the state to solve your conflict
  • Always fetch data needed from an external system, Just in time. This will increase the robustness of the step
  • Always create a step function that executes one piece of work at a time. Theoretically you can execute the whole workflow in a single step. However this does not help with traceability and reliability.

Workshop continued

The following pages try to introduce the workflow concept and how it relates to the product model. All code examples can be found in the example orchestrator .workflows.node directory. Please read at least the following pages to grasp the functionality of how workflows work and how the user/frontend will interact with the Orchestrator API: