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Can someone please provide insight into the support for shared subscriptions in EdgexFoundry's Jakarta 2.1 release. As indicated in this documentation, shared subscription feature appears to be exclusive to MQTT 5. But I was able to achieve shared subscription functionality using hivemq broker and $share topic syntax.

I've observed that even though EdgexFoundry Jakarta 2.1 doesn't support MQTT 5, I've managed to achieve shared subscriptions using the "hive mq" broker and the topic "$share/group/topic". I don't understand the reason behind this as ideally it shouldn't have supported shared subscription at all. Can someone please explain what is going on?

Deepsikha Bhattacharjee
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Just because Share Subscriptions is part of the MQTTv5 specification, there is nothing about it that stops it being implemented on a MQTTv3 broker (since all the implementation is broker side), in fact several brokers did this before the MQTTv5 specification was created, all be it with some minor differences.

Even when implemented in a MQTTv5 broker, a MQTTv3 client can connect and make use of the feature.

The reason it was added to the MQTTv5 specification was to ensure it was implemented in a fully consistent manner across all brokers going forward.

hardillb
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