[rabbitmq-discuss] Cluster failover behaviour

[Benjamin Black]

I apologize for not answering your Rabbit question.  What you are
describing is why you need an application-layer notion of idempotence.
It is at best frustrating and at worst dangerous to rely on a lower
level component, especially one written by someone else without this
exact use case in mind, to implement and enforce this sort of policy.


Best of luck,
b

On 12/14/09 2:13 PM, Robert Borkowski wrote:
> Hi,
> 
> Can you please help me understand what is going on when I lose a member of a
> cluster?
> I'm seeing an odd behaviour that makes me worry. This queue is supposed to
> hold
> credit card transactions, so we _really_ want to avoid double-processing
> messages.
> 
> Cluster consists of 2 members: (rabbit at mq1, rabbit at mq2).
> 
> 1) client connects to mq1, creates durable queue, pushes 100 persistent
> messages in
>     root at mq1:~# rabbitmqctl list_queues
>     Listing queues ...
>     testqueue       100
>     ...done.
> 
> 2) mq1 rabbitmq is stopped
> 
> 3) client connects to mq2, creates durable queue, pushes 100 persistent
> messages in
>     root at mq2:~# rabbitmqctl list_queues
>     Listing queues ...
>     testqueue       100
>     ...done.
> 
> 4) mq1 rabbitmq is started
>     root at mq2:~# rabbitmqctl list_queues
>     Listing queues ...
>     testqueue       200
>     ...done.
> 
> 5) client drains the queue
>     rborkows at mq1:~/client/bunny$ ./bunny-subscriber
>     Drained 200 messages in 0.475371 seconds
> 
> 6) queue is now empty
>     root at mq2:~# rabbitmqctl list_queues
>     Listing queues ...
>     testqueue       0
>     ...done.
> 
> 7) mq1 rabbitmq is restarted, 100 credit card transactions pop back into
> existence, unhappy customers, etc.
>     root at mq1:~# /etc/init.d/rabbitmq-server restart
>     Restarting rabbitmq-server: SUCCESS
>     rabbitmq-server.
>     root at mq1:~# rabbitmqctl list_queues
>     Listing queues ...
>     testqueue       100
>     ...done.
> 
> The expected behaviour is that after step 5 the messages are _gone_ from the
> queue, never to be seen again.
> What's going on here?
> 
> 
> 
> 
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