A scalable solution for server side push?

Question

I would like to implement a mechanism which will provide a RESTful API that allows a client to register interest in a subject with a sever, and receive asynchronous notifications from the server after the interest is registered. In enterprise (messaging) architecture, this is known as publish/subscribe 'pattern'.

With desktop applications, this is readily acheivable - however with web applications, it is proving to be more difficult.

is there a (preferably open source) framework or library out there that allows the publish/subscribe pattern to be applied to web applications?.

Server side technology may be in any of the following languages: C, C++, PHP, Python, Ruby.

I am running on Linux Ubuntu 10.0.4

Answer 1

Have a look at the pubsubhubbub protocol: http://en.wikipedia.org/wiki/PubSubHubbub

Here is the source of the project: http://code.google.com/p/pubsubhubbub/

Answer 2

If you know in advance you'll have a lot of subscribers (people/applications) that want notifications on a certain subject while on other hand you'll have few different subjects consider a pull technology anyway.

RSS, Atom are quite successful even though they use pull. The reason: no need to have an administration on the server of people who are subscribed, to detect who is no longer interested (client offline for a long time) or having a mechanism to get all the data out to the subscribers. Using push, you need to do very little on the server, while the clients will only pull a small amount of data everytime.

Pull costs slightly more bandwidth that's cheap anyway while it saves you a lot on CPU and software maintanance which is quite expensive.

Answer 3

I suggest you take a look at STOMP protocol, and its python clients (I use stomp.py). That should suit all your needs.