Implementing Workflow Versioning

In this lesson, you will learn how to safely evolve your background task logic without breaking active, in-flight workflow instances.

When using a workflow orchestrator, a single "process" might stay active for days or weeks. If you deploy new code that changes the task sequence or payload structure, existing instances—which are currently stuck in a "wait" state or paused at a specific step—might fail when they try to resume using logic that no longer matches their original state.

The Versioning Pattern

The most robust approach to this is Workflow Versioning via code branching or patching. Instead of overwriting existing task handlers, you treat your workflow definitions as immutable.

When you need to update logic, you create a new version of the workflow, often namespaced or tagged with a version identifier. You then implement a "version gate" within your worker logic to handle legacy state versus new state.

// Worker logic example using a version gate
async function processTask(instance) {
  const version = instance.version || 'v1';

  if (version === 'v1') {
    // Legacy logic: strict, original parameters
    return await legacyHandler(instance.data);
  } else {
    // New logic: updated steps or error handling
    return await modernHandler(instance.data);
  }
}

Managing Migrations

When your logic changes significantly (e.g., adding a new mandatory step in the middle of a process), you have two choices for active instances:

1. Drain and Complete: Allow legacy instances to finish using the old code path while routing all new requests to the new code path. This is the safest method.
2. State Transformation: If an instance must be upgraded, you perform a "state migration." You intercept the serialized state of the workflow, inject the new required fields or step markers into the JSON, and then resume the workflow using the new logic.

By keeping the code backward-compatible and using version tags in your task metadata, you ensure that a background process started last week doesn't crash just because you pushed a new deployment today.

Key Takeaway: Never update workflow logic in-place for active processes; use version tags and conditional branching to ensure legacy instances complete safely while new tasks adopt the updated workflow.