Update
Are there scenarios I need RabbitMQ
for web apps where Socket.io doesn't
suffice?
Browser users should be able to communicate with eachother through a node.js server. One
of the user writes a message and all other users will get it.
When you only have these simple requirements then socket.io alone will be enough.. You only need a message queue when you want to process your jobs(heavy) offline and in a controlled manner.
http://en.wikipedia.org/wiki/Message_queue:
Message queues provide an asynchronous
communications protocol, meaning that
the sender and receiver of the message
do not need to interact with the
message queue at the same time.
This sentence needs to sink in. The producer (one process) puts a job into the queue and the consumer consumes by taking the job from the queue. The consumer, most times, are multiple processes that consume multiple jobs concurrently. The consumers are unable to tell from each other, what jobs they are consuming.
This makes the queue a
First-In-First-Out (FIFO) data
structure.
That's I think an important property of the queue. The First-In-First-Out property although with an advanced message queue like beanstalkd you can give jobs priorities.
I hope this makes any sense at all ;)
I'm doing real time live web app
development.
Could you explain a little better so that we can give you a better answer?
I don't quite get how RabbitMQ works.
But from quick reading it seems that
it handles publication/subscription of
messages.
See the quote about message queue below. Let it sink in for a while. You could also read the WIKI about message queues.
A user (in a browser) publishes
something and subscribers (in other
browsers) get that message. Isn't that
what Socket.io is doing with
websockets?
Socket.io supports a lot of different transports(also websockets) and it should because websockets are not supported by the most browsers. But for example Google Chrome does already support websockets. I believe that websockets are the transport of the future(but not yet!). When you look at Socket.io's browser support page you will notice that Socket.io does support all the major browsers(some even ancient). The nice thing is that it wraps this around a nice API.
What are the advantages/disadvantages
for each one of them?
You are comparing apples to oranges so comparing that is kind of strange.
RabbitMQ
http://www.rabbitmq.com/tutorials/tutorial-one-python.html:
RabbitMQ is a message broker. The
principal idea is pretty simple: it
accepts and forwards messages. You can
think about it as a post office: when
you send mail to the post box you're
pretty sure that Mr. Postman will
eventually deliver the mail to your
recipient. Using this metaphor
RabbitMQ is a post box, a post office
and a postman.
Advantages
- It is a pretty good message queue. Personally I would use redis or beanstalkd.
Disadvantages:
- Is not really for "browsers".
Socket.io
http://socket.io/:
Socket.IO aims to make realtime apps
possible in every browser and
mobile device, blurring the
differences between the different
transport mechanisms.
Advantages
Disadvantages
- It is not a message queue.
Can Socket.io replace RabbitMQ?
No you can't because they are two completely different things. You are comparing apples to oranges. You should try to comprehend both descriptions from the sites I quoted.
