[mqtt-comment] Shared Subscriptions

[David Katz <David.Katz@bmw-carit.de>]

Hi all,

 

4.8.2 Shared Subscriptions

Scenario: backend servers are to respond to messages published to a given topic. In order to scale the backend applications, servers are added dynamically to the backend application cluster and subscribe to the MQTT server using Shared Subscriptions. To ensure that no messages are lost between broker and application cluster, QoS 1 and persistent sessions are being used. 

Question:  The specification at lines 3146-3151 "...  Server MAY wait for the Client to reconnect and retransmit the message to that Client.... the Server SHOULD send the Application Message to another Client.... It MAY attempt to send the message to another Client as soon as it loses its connection..." suggests that the Server is free to choose how to handle queueing and failover. If the server does not resend the message to another client, the message will however likely be lost. Shouldn't the correct behaviour be required by the spec?

 

Cheers,

David Katz

 

BMW Car IT GmbH
David Katz

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