Does OPC UA PubSub support multiple MQTT connections to the same broker and custom broker integration?

[sudhakar269]

Type of issue

• Bug
• Enhancement
• Compliance
• Question
• Help wanted

Current Behavior

Question

I'm using the OPC UA PubSub implementation in the .NET Standard stack and have two related questions:

1. Multiple MQTT Connections to the Same Broker

Can we configure multiple PubSubConnection entries that point to the same MQTT broker, with each handling a separate topic?

Example:

• PubSubConnection1 → mqtt://broker.example.com → topic: sensor/temperature
• PubSubConnection2 → mqtt://broker.example.com → topic: sensor/humidity

Will these operate as independent MQTT connections? Or is it recommended to use a single connection with multiple WriterGroups?

---

2. Custom Broker Support

Is it possible to integrate a custom broker (e.g., Kafka, ZeroMQ, Redis Streams) into the PubSub model?

• Does the stack support custom transport protocols?
• Is there a way to implement a custom broker handler or adapter?

Expected Behavior

No response

Steps To Reproduce

No response

Environment

- OS:Windows 10
- Environment:.NET development (Visual Studio / C#)  
- Runtime:
- Nuget Version:
- Component:
- Server:
- Client:

Anything else?

No response

[mrsuciu]

@sudhakar269

1. Multiple MQTT Connections to the Same Broker:

Yes, you can create multiple pub sub connections that point to the same MQTT broker, each handling a separate topic.
They operate as independent MQTT connections to the MQTT broker.
See internals and usage of private static PubSubConfigurationDataType CreatePublisherConfiguration_MqttJson as an example.
The QueueName and MetaDataQueueName are used as topic matches in the MQTT transport layer for data and meta-data consumption.

2. Custom Broker Support

The specification defines the following PubSub transport profiles [PubSub UDP UADP, PubSub MQTT UADP, PubSub MQTT JSON, PubSub AMQP UADP, PubSub AMQP JSON] and the current implementation supports the first three of them, see https://profiles.opcfoundation.org/profilefolder/320