Multi-Consumer Fanout

Fanout is a pattern where a single Business Event is consumed by multiple independent consumers simultaneously. Because Business Events is a pub/sub system, publishers do not need to know how many consumers exist — each consumer subscribes independently.

One event, many consumers

flowchart LR
    P[Publisher\nNotebook / UDF / Eventstream] -->|Publishes| BE[Business Event\nRetail.Sales.VolumeAlert]
    BE --> A[Activator\nSend Teams alert]
    BE --> B[Eventhouse\nStore for analytics]
    BE --> C[Activator\nTrigger reorder pipeline]

Each consumer subscribes independently. Adding a new consumer does not require any change to the publisher.

Common fanout patterns

Alert + analytics

The most common combination — one consumer reacts in real time, another stores for historical analysis.

flowchart LR
    P[Publisher] --> BE[Business Event]
    BE --> ACT[Activator\nReal-time alert]
    BE --> EH[Eventhouse\nHistorical analytics]

When to use: Any event where you need both immediate action and long-term visibility.

Alert + automation

Two Activator consumers with different actions — one notifies a human, another triggers an automated workflow.

flowchart LR
    P[Publisher] --> BE[Business Event]
    BE --> A1[Activator Rule 1\nSend email notification]
    BE --> A2[Activator Rule 2\nTrigger Power Automate flow]

When to use: When a signal requires both human awareness and an automated response, and you want to manage them independently.

Cross-domain fanout

A single business signal consumed by teams in different domains, each with their own logic.

flowchart LR
    P[Publisher\nRetail workload] --> BE[Business Event\nRetail.Customer.MilestoneReached]
    BE --> A[Marketing team\nActivator → loyalty email]
    BE --> B[Analytics team\nEventhouse → cohort analysis]
    BE --> C[Finance team\nActivator → discount approval]

When to use: When a business signal has value across multiple teams or domains, and each team should own their consumer independently.

How to set up fanout

Each consumer is created independently — there is no fanout configuration on the publisher side.

Consumer	How to add
Activator	Real-Time Hub → Business events → Set alert → configure new rule
Eventhouse	Enabled at Business Event creation time via the "Analyze in Eventhouse" checkbox

To add a second Activator consumer, simply create a new alert rule on the same Business Event. The two rules run independently and do not interfere with each other.

Design considerations

Keep consumers independent. Each consumer should be able to fail, restart, or be updated without affecting others.

Do not use fanout to sequence work. If Consumer B must run after Consumer A completes, fanout is not the right pattern — use a dedicated orchestration mechanism instead.

Monitor each consumer separately. A delivery failure to one consumer does not affect delivery to others. Track consumer health individually.