Hello, I am currently investigating flespi for a project and ran into the following issue: When setting up 2 clients on the same Shared Subscription and both with a persistent Session, all messages are enqueued to the first client when both clients are offline. This is the flow: Connect Consumer A, subscribe to '$share/some-group/telemetry/#' Connect Consumer B, subscribe to '$share/some-group/telemetry/#' Take both clients offline Disconnect all clients Connect publisher A and send 30 messages Connect client A and client B again All messages go to Consumer A. My expectation was that the broker would load balance even when no subscribers are connected. Is my expectation wrong or did I make a mistake? See https://www.codepile.net/pile/pa4ONJ54 for code

Combining Shared Subscriptions and Persistent Session

ImmanuelPelzer

Hello,

I am currently investigating flespi for a project and ran into the following issue:

When setting up 2 clients on the same Shared Subscription and both with a persistent Session, all messages are enqueued to the first client when both clients are offline.

This is the flow:

Connect Consumer A, subscribe to '$share/some-group/telemetry/#'
Connect Consumer B, subscribe to '$share/some-group/telemetry/#'
Take both clients offline
Disconnect all clients
Connect publisher A and send 30 messages
Connect client A and client B again

All messages go to Consumer A.

My expectation was that the broker would load balance even when no subscribers are connected.

Is my expectation wrong or did I make a mistake?

See https://www.codepile.net/pile/pa4ONJ54 for code

baja

ImmanuelPelzer You have specified session as non-clean. It means that even if the client disconnects - it buffers messages (as if it was connected), the buffered messages are delivered after client re-connection.
What if you specify client A as non-clean (thus it won't lose any message on disconnect), and client B as clean (thus when it disconnects - client A will be the only active session and theoretically receive or buffer all the messages) ?

adsa

ImmanuelPelzer

Please take a look: https://forum.flespi.com/d/19-changelog-flespi-mqtt-broker/29

ImmanuelPelzer

Thanks for the response.

I want all consumers to be non-clean. My question is regarding a potential HA setup: If for some reason all consumers (subscribers) are offline, all messages will be queued to the same consumer.

This means once the consumers come back online, all messages are flushed onto one consumer instead of being load-balanced between all of them.

dexif

ImmanuelPelzer
As far as I can see, this behavior is not described in the mqtt protocol documentation.
We will consider reworking this behavior.
But at the moment the implementation is as you see it.