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Workflows4s Architecture

System Components​

The diagram below illustrates the key components of Workflows4s and their relationships:

Key Concepts​

Core Components​

  • Your Business Logic: Your application code that defines the workflow steps and business rules.
  • WIO (Workflow Definition): A pure value object that describes the workflow structure, e.g.:
    • Steps (computations)
    • Signal handling
    • Timers
    • Branching

Runtime Components​

  • WorkflowRuntime: Manages workflow instances and their execution.
  • Runtime Dependencies: External services required by the runtime (e.g., event storage).
  • WorkflowInstance: A specific execution of a workflow with a unique ID.
  • Events: Persistent records of all actions and state changes in the workflow.
  • KnockerUpper: Responsible for waking up workflows at scheduled times, handling timer-based operations.

Interaction Methods​

  • createInstance: Creates a new workflow instance with a specific ID.
  • queryState: Retrieves the current state of a workflow instance.
  • wakeup: Resumes a paused workflow instance.
  • deliverSignal: Sends external signals to a workflow instance.

Visualization​

  • Renderer: Converts workflow definitions into visual representations.
  • Static Visualization: Shows the complete workflow structure before execution.
  • Progress Visualization: Shows the current state and progress of a running workflow.

Execution Model​

Workflows4s uses an event-sourcing approach:

  1. First Run: The workflow executes operations along its path, with each operation producing an event that is persisted.
  2. Recovery: After a restart, events are read from storage and applied to rebuild the workflow state without re-executing side effects.
  3. Signals: External events can be delivered to the workflow to trigger state transitions.

This architecture enables workflows to be resilient, recoverable, and visualizable throughout their lifecycle.