[rabbitmq-discuss] RabbitMQ production setup questions around clustering

Dave Greggory davegreggory at yahoo.com
Thu Jul 22 14:20:28 BST 2010

Thanks, Alex. That clears up a lot. 

Looks like I will be setting up a 2 node cluster with both nodes as disc nodes (as that's the only way to recover from a permanent failure of a disc node). I will have clients connect through the node-switcher/load-balancer with the insist flag on.

On Thu Jul 22nd, 2010 8:05 AM EDT Alexandru Scvortov wrote:

>Hi Dave,
>> Questions:
>> 2. When a queue is declared (by one of our producers), is the queue always
>> created on the rabbitmq node the producer client has a connection to or is the
>> queue created on a randomly selected node within the cluster?
>The queue is created only on that one node, but is accessible from all
>nodes in the cluster.  All nodes in the same cluster are functionally
>interchangeable, i.e. it doesn't matter which of the nodes you connect to,
>you can still use the queue.
>> 3. If the queue is durable and the messages sent to it are marked persistent,
>> will these messages always be persisted to disk and be available after a restart
>> of the node that has that queue, regardless of whether the node is a disk node
>> or RAM node? (This line "Should you do this, and suffer           a power
>> failure to the entire cluster, the entire state of           the cluster,
>> including all messages, will be lost.         " in
>> http://www.rabbitmq.com/clustering.html is confusing)
>The distinction between RAM and disk nodes refers to where the Mnesia
>tables are stored.  The routing configuration (what queues there are,
>which exchanges they're bound to, etc.) is stored in Mnesia, so at least one
>of the nodes should be a disk node.  This way, if both nodes go down
>at the same time (power failure), when they're restarted, the cluster
>should spring back to life just like before.
>Messages are persisted to disk, regardless of whether the node is a
>disc node or not.  Also, messages are persisted to disk only on the node
>on which the queue was declared.  If said node is a RAM node and it goes
>down, it won't lose the messages; when it reconnects to the cluster, the
>queue should just get recreated (assuming it was declared as durable).
>If both nodes are RAM nodes, and they both go down, when they're
>restarted, they won't know what queues were declared, etc.  So, in this
>case, the messages will be lost.
>> 4. Should I configure both my nodes as disk nodes or will one disk node be
>> sufficient? In other words, if only 1 disk node was there in the cluster and its
>> hard drive went bust, what can I recover from the RAM node? If nothing can be
>> recovered from the RAM node
>As mentioned above, the RAM node will not store the routing configuration to disk.
>If the disc node goes down, you should still be able to recover the broker
>configuration from it by adding a new disc node to the cluster.
>If any of the nodes goes down permanently (disk failure, etc.), the
>messages stored on it will be lost.  If you don't want this to happen,
>have a look at the HA Clustering guide:
>  http://www.rabbitmq.com/pacemaker.html
>> is it mainly for increasing the number of
>> connections without taking any hits to disk throughput?
>Pretty much, yes.
>> 5. Are connections redirects actually supported by the current version? The FAQ
>> and Clustering documents on site are contradictory of each other. (FAQ says
>> "Future releases will support live failover using, for 	      instance, a
>> combination of the "known hosts" field in connection.open-ok and the
>> connection.redirect message.")
>> 6. If redirects are supported, when all connections are being sent to a specific
>> rabbitmq node in the cluster by the loadbalancer, will that rabbitmq node still
>> send a redirect request to the client if it's getting too taxed? If so, then is
>> it possible to limit redirects to only the disk nodes within the cluster so that
>> we don't lose any data?
>> 7. Will the connections be redirected solely based on RabbitMQ node's ability to
>> serve it or is it more round-robin?
>There is currently some loadbalancing done via AMQP's connection.redirect
>Both redirects and loadbalancing will soon be removed from RabbitMQ.  It
>would probably be better if you didn't count on this feature.
>> 8. Is there a way to ensure that the cluster configuration is correct because
>> 'disc/RAM' is not reported correctly by rabbitmqctl (as per
>> http://old.nabble.com/Rabbitmq-v.-1.8.1---Bug-report---Could-not-start-a-node-as-RAM-node-in-cluster-ts29211668.html)?
>Not in the current release, no.  It's been fixed on the develpment branch
>and should make it into the next release.
>Hope this clears things up.


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