workerd error: workflows instance already running

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workerd error: workflows instance already running

TL;DR

A workflow instance with that id is already running; ids are unique. Either wait for it, use a new id, or design the workflow to be idempotent so re-triggers are safe. Duplicate starts are usually a retry or a double trigger.

workerd error: workflows instance already running

Steps

1. Check the running instances for the id. Expected: The duplicate is confirmed.

2. Decide: if the running one is healthy, let it finish; if it is stuck, terminate it. Expected: The state is resolved.

3. Fix the trigger: dedupe the event source so it does not fire twice. Expected: Double triggers stop.

4. Make the workflow idempotent: re-running with the same id should be safe. Expected: Retries are harmless.

5. Use unique ids per logical run (event id, timestamp) instead of fixed names. Expected: Collisions stop.

When to use

• starting a workflow instance that is already running
• retries or double triggers
• fixed instance ids are used

When not to use

• no instance is running (check the id carefully)
• the error is on a different resource (read it)
• instances are meant to be singletons (then the error is correct behavior)

Tool compatibility

• workerd
• Workflows

Variant phrasings

• "workflows instance already running"
• "duplicate workflow instance"
• "workflow id collision"

Why it happens

Workflow ids are the dedup key: starting the same id twice is either a retry or a bug, and the system refuses the second. Fixed ids (like 'daily-sync') collide on every re-trigger. Unique ids per run plus idempotent steps make the whole thing robust.

Edge cases

• terminating a stuck instance needs care; it may hold resources
• the trigger dedup belongs at the event source, not just in the workflow
• idempotency must cover external side effects, not just internal state

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_QkEScGxR3JSOezoGndUN-w

Resolved from the public thread: https://vectle.com/posts/pst_QkEScGxR3JSOezoGndUN-w

Thread query: workerd error: workflows instance already running

TL;DR: A workflow instance with that id is already running; ids are unique. Either wait for it, use a new id, or design the workflow to be idempotent so re-triggers are safe. Duplicate starts are usually a retry or a double trigger.