Could you please let me know if in any of the cluster 2 rabbitmq are
running and suddenly both the rabbitmq node are down and then any of the
node come back then there will be a messages loss or data loss?


Or application become down until we restart the whole cluster?


Please provide me an answer of my query?
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  • Simon MacMullen at Dec 13, 2012 at 11:04 am

    On 13/12/12 08:15, Vikrant Sayeewal wrote:
    Could you please let me know if in any of the cluster 2 rabbitmq are
    running and suddenly both the rabbitmq node are down and then any of the
    node come back then there will be a messages loss or data loss?

    Assuming that you have published persistent messages to durable queues,
    you will not lose any messages for which your publisher has received
    confirmations. Non-persistent messages and non-durable queues will be
    lost, and any messages which were in flight (i.e. you have not received
    confirmations) may or may not be lost depending on where they were when
    the cluster went down.


    Note also that if node B goes down first, *then* node A, then node A
    will have to come back before node B will work (since node B cannot
    trust its copy of the cluster state; other things may have happened
    while it was down). If node A is not going to come back you can use
    "rabbitmqctl forget_cluster_node".

    Or application become down until we restart the whole cluster?

    Not quite sure what you mean here, hopefully my answer above helps.


    Cheers, Simon


    --
    Simon MacMullen
    RabbitMQ, VMware
  • Vikrant Sayeewal at Dec 13, 2012 at 11:10 am
    If both the available rabbitmq nodes goes down then it means, I need to
    restart whole cluster in place of restarting those nodes??


    And there might be a chance of messeges loss??
    Is this is what you try explain?




    On Thu, Dec 13, 2012 at 1:45 PM, Vikrant Sayeewal wrote:

    Could you please let me know if in any of the cluster 2 rabbitmq are
    running and suddenly both the rabbitmq node are down and then any of the
    node come back then there will be a messages loss or data loss?

    Or application become down until we restart the whole cluster?

    Please provide me an answer of my query?
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  • Tim Watson at Dec 18, 2012 at 1:28 pm

    On 13 Dec 2012, at 11:10, Vikrant Sayeewal wrote:


    If both the available rabbitmq nodes goes down then it means, I need to restart whole cluster in place of restarting those nodes??

    Restarting a single node *should* be enough, but caveats apply. If you published to node 1 and that message was non-persistent, then node 1 dies *before* the message can be relayed to node 2 (for example if the network between the two nodes becomes slow or unavailable during that time) then the message could be lost. As Simon points out, you need to use persistent messages to make sure they survive.


    Another scenario in which message loss can occur even when messages are persistent is that you publish to node 1 and it dies before transmitting the message to node 2 **and** before writing the message to disk.


    The solution to this is to use publisher confirms. When confirms are enabled (setting the channel to confirm mode) and messages are persistent, then the broker will not send a confirm.ok until the message has been written to disk *and* the i/o buffer has been flushed/synchronised. The broker will also ensure that the message has been transmitted to node 2 and confirmed as persisted there. In this case, no message loss will occur such that once you have seen a confirm for the message, even if both nodes go down, restarting one node will be enough to access the message.


    Cheers,
    Tim

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