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

[Tony Garnock-Jones]

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
message).

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.

Regards,
  Tony
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