Subscribe to Southbound Data
A northbound application receives nothing until it explicitly subscribes to a southbound collection group. Once subscribed, that group's data is published to the application at the group's polling interval.
Subscriptions work per group — you cannot subscribe to only some tags within a group. To publish tags separately, split them into different groups on the southbound side; see Grouping strategy.
Add a subscription
Click the northbound application card to open the Group List page, then click Add Subscription:
Field | Description |
|---|---|
| Topic | The upload topic. Needed only for MQTT-based applications and Kafka; a default is used when left blank |
| Subscription South Driver Data | Tick the collection groups to subscribe to. Expand a driver node to pick its groups; groups from different drivers can be ticked together and submitted as several subscriptions at once |
| Static Tags | Optional. Fixed attributes published alongside the group's data, given as JSON key-value pairs — see Static tags |
For MQTT and AWS IoT the default upload topic is /neuron/{application}/{driver}/{group}. Kafka falls back to the default topic in the application configuration. Azure IoT, Sparkplug B, OPC UA Server, and WebSocket derive their topic or node path from the protocol specification, so there is nothing to specify per subscription.
How subscriptions relate
A subscription is identified by the combination of southbound driver, group, and northbound application. As a result:
- One application can subscribe to many groups, including groups from different drivers.
- One group can be subscribed by many applications, so the same collected data can go to the cloud, be read by an upper-level system, and land in a data platform at the same time, independently of each other.
- The same application can subscribe to a given group only once.
Removing a subscription stops publishing that group to that application; collection on the southbound side is unaffected.
Verify
After subscribing, click Data Statistics on the northbound application card — send_msgs_total should keep increasing. If it does not, check in order that the southbound driver is Running and Connected, the northbound application is Running, and the subscription exists. For the statistics fields, see Create a Northbound Application.