[rabbitmq-discuss] A question about RabbitMQ "Presence Exchange" Plugin

Tony Garnock-Jones tonygarnockjones+rabbitmq at gmail.com
Wed Feb 8 12:44:54 GMT 2012

On 8 February 2012 07:17, Marek Majkowski <majek04 at gmail.com> wrote:

> Take a look at the readme:
> https://github.com/tonyg/presence-exchange#readme
> "bindings made with the empty string "" as their binding
> key, which receive presence messages, but do not
> produce them; and bindings made with any other binding key,
> which produce presence messages but do not receive them."

Also, remember that queues can bind to the same exchange more than once! So
it's perfectly acceptable for some queue to bind twice to a
presence-exchange, once with key "" (in order to *receive* presence
messages) and again with key "myname" (in order to *issue* a presence

The reason it is the way it is is so that asymmetrical situations can be
cooked up on demand. Binding twice is one easy way of producing a
symmetrical situation.

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