Preventing Stale Data: Ensuring Event Group TTLs in ESHOPMAN's Redis Event Bus

Preventing Stale Data: Ensuring Event Group TTLs in ESHOPMAN's Redis Event Bus

For ESHOPMAN, a headless commerce platform built on Node.js/TypeScript and integrated with HubSpot for storefront management, efficient and reliable event handling is fundamental. Our event bus orchestrates critical workflows, from order processing to inventory updates, ensuring smooth operations and data integrity across your HubSpot-deployed storefront.

A recent community insight revealed a critical issue within ESHOPMAN's Redis Event Bus module that could lead to an accumulation of stale data. This discussion details the problem, its implications for ESHOPMAN developers and merchants, and the recommended solution to ensure your event groups are always properly managed.

The Core Issue: Unexpiring Staged Events

ESHOPMAN's Redis Event Bus service stages grouped events in Redis lists, typically at keys like staging:. The design intends to guard these lists with a Time To Live (TTL), preventing stale data from persisting indefinitely if a workflow fails. However, a subtle bug was discovered: the EXPIRE command, meant to set the TTL, is issued before the RPUSH command that actually creates the Redis key.

Since an EXPIRE command against a non-existent key is a no-op, the TTL is silently never applied on a group's first emit(). The expiry only successfully lands on subsequent emit() calls for the same group. Consequently, any event group whose events are all emitted in a single call will end up with a list that has no expiry.

for (const [groupId, events] of groupEventsMap.entries()) {
  if (!events?.length) {
    continue
  }

  // Set a TTL for the key of the list that is scoped to a group
  // This will be helpful in preventing stale data from staying in redis for too long
  // in the event the module fails to cleanup events.
  void this.setExpire(groupId, groupedEventsTTL) // EXPIRE issued here

  const eventsData = this.buildEvents(events, options)

  promises.push(this.groupEvents(groupId, eventsData)) // RPUSH happens within groupEvents
}

Why This Matters for Your ESHOPMAN Storefront

This oversight has significant implications for your ESHOPMAN environment:

• Resource Leakage: If a workflow process crashes or exits prematurely (e.g., during a custom script via the Admin API), unreleased, unexpired lists accumulate indefinitely in your Redis instance.
• Performance Impact: An ever-growing number of unmanaged keys consumes Redis memory and can impact performance for other critical ESHOPMAN operations.
• Monitoring Blind Spots: These staging:* keys sit outside typical queue metrics, making the leak difficult to detect until it becomes a significant problem.

The Recommended Fix: Atomic TTL Application

The solution involves ensuring the EXPIRE command is issued *after* the RPUSH and, critically, within the same Redis pipeline. This guarantees atomicity and that the TTL is applied the moment the key is created. The suggested modification to the groupEvents function ensures every staging: list carries its configured groupedEventsTTL (default 600s) from its inception.

private async groupEvents(
  eventGroupId: string,
  events: IORedisEventType[],
  ttl: number
) {
  const key = `staging:${eventGroupId}`
  const pipeline = this.eventBusRedisConnection_.pipeline()
  pipeline.rpush(key, ...events.map((event) => JSON.stringify(event)))
  pipeline.expire(key, ttl) // EXPIRE now happens after RPUSH in the same pipeline
  await pipeline.exec()
}

This approach also improves error observability, unlike the previous fire-and-forget void call.

A Related Observation: Empty RPUSH in ClearGroupedEvents

A minor related point: the clearGroupedEvents function could issue an RPUSH command with no members if all staged events in a group are cleared. While the group is correctly emptied by a preceding del, this results in an ERR wrong number of arguments error in the pipeline. Guarding the rpush with a check for a non-empty eventsToKeep array would resolve this.

Conclusion

Addressing this Redis TTL bug is crucial for maintaining a clean, efficient, and robust ESHOPMAN environment. By implementing this fix, ESHOPMAN developers can ensure proper management of staged event data, preventing resource leaks and contributing to a more stable headless commerce experience for merchants leveraging HubSpot CMS. This highlights the value of community-driven insights for platform health.