Reference IDs

Reference IDs let you assign custom identifiers to workflows, events, and schedules. This enables tracking, correlation with your systems, and lookup by your own IDs. As a secondary benefit, reference IDs prevent duplicate executions when the same reference is reused.

What are Reference IDs?

A reference ID is a custom identifier you provide when starting a workflow, sending an event, or activating a schedule. Use cases include:

• Tracking: Correlate Aiki workflows with your order IDs, user IDs, or transaction IDs
• Lookup: Find a workflow run using your own identifier instead of Aiki's internal run ID
• Duplicate prevention: When a reference ID is reused, Aiki can either throw an error, return the existing run, or silently deduplicate (for events)

Reference IDs are unique per workflow version (workflow name + version ID). The same reference ID can be used across different workflow versions without conflict.

Note: Tasks do not support reference IDs. Tasks are content-addressed by name + hash(input) — see Content-Addressed Memoization for how this works.

Workflow Reference IDs

When starting workflows, you can provide a reference ID:

// Start a workflow with a reference ID
const handle = await orderWorkflowV1
  .with("reference.id", "order-123")
  .start(client, { orderId: "order-123", items: [...] });

// You can now look up this workflow using "order-123"
// If you try to start another workflow with the same reference ID,
// Aiki will throw an error by default (configurable via conflictPolicy)

Conflict Handling

By default, Aiki throws an error when you try to start a workflow with a reference ID that already exists but with different input. You can configure this behavior with the conflictPolicy option:

// Default behavior: throw error on conflict
const handle = await orderWorkflowV1
  .with("reference", { id: "order-123-process", conflictPolicy: "error" })
  .start(client, { orderId: "order-123", items: [...] });

// Alternative: return existing run on conflict
const handle = await orderWorkflowV1
  .with("reference", { id: "order-123-process", conflictPolicy: "return_existing" })
  .start(client, { orderId: "order-123", items: [...] });

// With "return_existing", duplicate calls return the same workflow run
// handle.id will be the same as the original run

Event Reference IDs

When sending events to a workflow, you can provide a reference ID to prevent duplicate event delivery:

// Send an event with a reference ID
await handle.events.approved
  .with("reference.id", "approval-123")
  .send({ by: "manager@example.com" });

// If the same event is sent again with the same reference ID,
// it will be silently ignored (no error, no duplicate)
await handle.events.approved
  .with("reference.id", "approval-123")
  .send({ by: "manager@example.com" }); // Ignored - duplicate

// Without options, use send directly
await handle.events.approved.send({ by: "manager@example.com" });

Unlike workflows, events use silent deduplication - duplicate events are simply ignored rather than throwing an error.

Schedule Reference IDs

When activating schedules, you can provide a reference ID for explicit identity:

const handle = await dailyReport
	.with("reference", {
		id: "tenant-acme-daily-report",
		conflictPolicy: "error",
	})
	.activate(client, reportWorkflowV1, { tenantId: "acme" });

Schedules use the same conflict policies as workflows:

A schedule's definition is immutable, so a reference ID that already points at a different definition is a conflict, never an update. "error" throws a ScheduleConflictError; "return_existing" hands back the existing schedule as-is.

See the Schedules documentation for more details.

How It Works

Workflow Level

When you provide a reference ID when starting a workflow, the system checks if a workflow run with that ID already exists. Based on the conflictPolicy setting:

• "error" (default): Throws an error if a run exists with different input
• "return_existing": Returns the existing workflow run

Benefits of Reference IDs

Reference IDs provide several benefits:

• External correlation: Track workflows using your own identifiers (order IDs, user IDs, etc.)
• Lookup capability: Find workflow runs by reference ID instead of internal run IDs
• Duplicate prevention: Prevent accidental duplicate workflow or event executions when retrying requests