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Subject: [OASIS Issue Tracker] (MQTT-260) Add a CONNACK code of 'Try Another Server'


    [ https://issues.oasis-open.org/browse/MQTT-260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=63607#comment-63607 ] 

Andrew Banks commented on MQTT-260:
-----------------------------------

This needs to be specific about whether the other server contains all of the same state as the original server. 

There are two possibilities.

1) The other server has exactly the same state as the original, the client can connect with the same clientid, userid ,password and 
   continue  sending and receiving messages using a single version of its state. It does not need to remake durable subscriptions.

2) The server does not have a copy of the state that was in the original server. The client must use another set of state at its end. It might use different credentials to connect  to the other server and it might have to remake its subscriptions if it had not previously made them to the other server.



> Add a CONNACK code of 'Try Another Server'
> ------------------------------------------
>
>                 Key: MQTT-260
>                 URL: https://issues.oasis-open.org/browse/MQTT-260
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 5
>            Reporter: Raphael Cohn
>            Assignee: Raphael Cohn
>            Priority: Critical
>
> If we add a CONNACK return code of 'Try Another Server', this makes it easier for over-loaded servers to tell clients to redirect. This works in conjunction with MQTT-259, which advocates the use of DNS SRV records.
> Indeed, if we also added server-originated DISCONNECT packets with this return code, we could get clients to cleanly migrate to another server when a server is shutdown for maintenance.
> Please note, I do not favour the server also reporting which new server to connect to. There in lies the route to madness, as it means the current server has to know the state of all the others. That's intimate knowledge.



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