Hi Rabbit MQ Team,
? ? I am reading your HA documentation-
http://www.rabbitmq.com/ha.html?


The following statement under "Mirrored Queue?Behavior" seems to have typo.

"All actions other than publishes go only to the master, and the master then broadcasts the effect of the actions to the slaves. Thus clients consuming from a mirrored queue are in fact consuming from the master."

The first?statement?should be-
All actions other than publishes go only to the?SLAVE, ... (instead of master)


Am i correct?

Side Note: Pl correct the spelling for "Behavior" in the title.

Thanks,
-Uday.
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  • Emile Joubert at Feb 10, 2012 at 10:04 am
    Hi Uday,
    On 09/02/12 23:32, Uday Subbarayan wrote:
    The first statement should be-
    All actions other than publishes go only to the SLAVE, ... (instead of
    master)
    No, the statement as it stands is correct. This thread has some more detail:
    http://lists.rabbitmq.com/pipermail/rabbitmq-discuss/2012-February/017957.html
    Side Note: Pl correct the spelling for "Behavior" in the title.
    Both are correct. The RabbitMQ team tend towards British spelling.



    -Emile
  • Uday Subbarayan at Feb 10, 2012 at 7:50 pm
    Hi Emile,
    ? ? ?I read all the documentation + mailing list and can understand from past experience that HA in MQ is not a simple task. Here is my understanding to setup HA in Rabbit MQ and pl correct me if i am wrong

    Step -0: Setup 2 nodes.

    Node -1 : Master
    Node -2: Slave

    Step -1: Configure Mirrored Queues

    Step-2: Publish Message to Master
    "This is why publishes *also* go via GM - the master?pushes each publish onto GM and the slaves received that and use it to?derive the correct order" -?Matthew Sackman@ Rabbit MQ

    Step -3:Let?Guaranteed Multicast(GM) to replicate messages to slaves

    Step-4: Consume messages from slaves

    Note: There is a risk in the above strategy if the master node goes down. If you want to avoid, then publish to all slaves? Here on wards, i am not clear. I also read about putting HA Proxy in front of the Rabbit MQ cluster and don't know whether it can lead to better or worse in this complex mix :-)

    It looks to me that my steps can get basic level of HA in Rabbit MQ! Pl correct if i am wrong.

    Best,
    -Uday.


    ________________________________
    From: Emile Joubert <emile at rabbitmq.com>
    To: Uday Subbarayan <uday.subbarayan at yahoo.com>
    Cc: "rabbitmq-discuss at lists.rabbitmq.com" <rabbitmq-discuss at lists.rabbitmq.com>
    Sent: Friday, February 10, 2012 2:04 AM
    Subject: Re: [rabbitmq-discuss] HA Documentation Error?

    Hi Uday,
    On 09/02/12 23:32, Uday Subbarayan wrote:
    The first statement should be-
    All actions other than publishes go only to the SLAVE, ... (instead of
    master)
    No, the statement as it stands is correct. This thread has some more detail:
    http://lists.rabbitmq.com/pipermail/rabbitmq-discuss/2012-February/017957.html
    Side Note: Pl correct the spelling for "Behavior" in the title.
    Both are correct. The RabbitMQ team tend towards British spelling.



    -Emile
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  • Emile Joubert at Feb 13, 2012 at 10:15 am
    Hi Uday,
    On 10/02/12 19:50, Uday Subbarayan wrote:
    Note: There is a risk in the above strategy if the master node goes
    down. If you want to avoid, then publish to all slaves? Here on wards, i
    If the master becomes unavailable then a slave is promoted to take its
    place. Message replication between slaves and the master happens
    internally and automatically. As long as the queue is declared as
    mirrored, the publisher is not required to take any action to republish
    messages to slaves.
    am not clear. I also read about putting HA Proxy in front of the Rabbit
    MQ cluster and don't know whether it can lead to better or worse in this
    complex mix :-)
    Active-active mirrored queues are recommended instead of the
    active-passive approach, because it does not require additional software
    and the failover process is quicker.


    -Emile
  • Matthew Sackman at Feb 16, 2012 at 11:14 am

    On Mon, Feb 13, 2012 at 10:15:16AM +0000, Emile Joubert wrote:
    On 10/02/12 19:50, Uday Subbarayan wrote:
    Note: There is a risk in the above strategy if the master node goes
    down. If you want to avoid, then publish to all slaves? Here on wards, i
    If the master becomes unavailable then a slave is promoted to take its
    place. Message replication between slaves and the master happens
    internally and automatically. As long as the queue is declared as
    mirrored, the publisher is not required to take any action to republish
    messages to slaves.
    Well, that's not necessarily true. If the node that failed was also the
    node to which the client was connected, then the client needs to detect
    the death of the connection, establish a new connection to a surviving
    node and then republish all messages that it never got
    publisher-confirms back for - assuming the client even turned
    publisher-confirms on. That would be the only way to ensure
    at-least-once delivery.
    Active-active mirrored queues are recommended instead of the
    active-passive approach, because it does not require additional software
    and the failover process is quicker.
    However, throughput is lower, and it does not have any chance of
    integration with other clustering/HA software elsewhere in the stack.

    Matthew
  • Uday Subbarayan at Feb 23, 2012 at 9:41 pm
    Thanks Matt. It would be nice if the HA documentation is revisited again and?explain the basic steps well, it's of great help to the community.

    Best,
    Uday.?
    ?


    ________________________________
    From: Matthew Sackman <matthew at rabbitmq.com>
    To: rabbitmq-discuss at lists.rabbitmq.com
    Sent: Thursday, February 16, 2012 3:14 AM
    Subject: Re: [rabbitmq-discuss] HA Documentation Error?
    On Mon, Feb 13, 2012 at 10:15:16AM +0000, Emile Joubert wrote:
    On 10/02/12 19:50, Uday Subbarayan wrote:
    Note: There is a risk in the above strategy if the master node goes
    down. If you want to avoid, then publish to all slaves? Here on wards, i
    If the master becomes unavailable then a slave is promoted to take its
    place. Message replication between slaves and the master happens
    internally and automatically. As long as the queue is declared as
    mirrored, the publisher is not required to take any action to republish
    messages to slaves.
    Well, that's not necessarily true. If the node that failed was also the
    node to which the client was connected, then the client needs to detect
    the death of the connection, establish a new connection to a surviving
    node and then republish all messages that it never got
    publisher-confirms back for - assuming the client even turned
    publisher-confirms on. That would be the only way to ensure
    at-least-once delivery.
    Active-active mirrored queues are recommended instead of the
    active-passive approach, because it does not require additional software
    and the failover process is quicker.
    However, throughput is lower, and it does not have any chance of
    integration with other clustering/HA software elsewhere in the stack.

    Matthew
    _______________________________________________
    rabbitmq-discuss mailing list
    rabbitmq-discuss at lists.rabbitmq.com
    https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
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