Awesome

Terms

Comet

Reverse AJAX, server push. It's a method to push data from a server to the web clients without the need to do polling.

Comet server/solutions

Orbited

Implementation of Comet using a push server in Python that can interact with a wide variety of messaging protocols such as STOMP, IRC, XMPP, etc. http://orbited.org

Stream-Hub

It's a commercial project with a "free" community edition limited to 10 concurrent users. http://www.stream-hub.com/

Meteor

It's a free server implementation of Comet written in Perl. (http://meteorserver.org)

It's CPU intensive. Separating the comet server from the web server using ports won't work in Safari 2 or Opera. It doesn't support XMPP Protocol It doesn't support authentication?

For an overview of existing solutions please visit theComet server comparison matrix

Protocols

Stomp (Streaming Text Orientated Messaging Protocol)

Stomp is an interoperable procotol for the exchange of messages between different programming languages, platforms and brokers.

XMPP (Extensible Messaging and Presence Protocol)

Open technology for real time communication used Tecnología abierta para la comunicación en tiempo real utilizada mayormente para mensajería instantánea, alerta de presencia, chat multiusuario, llamadas de video y voz, etc. etc. Fue desarrollada inicialmente por la comunidad Jabber.

Setup with Rails app + Orbited

Install Orbited server (on Ubuntu)

Make sure build-essential python and python-dev are installed (via apt)
Install setuptools: sudo aptitude install python-setuptools
Install twisted: sudo easy_install twisted
Install orbited: sudo easy_install orbited)
Check to see if orbited was installed correclty: open python interactive console with "python" and "import orbited". If you see no error you are good.
Install cjson: sudo aptitude install python-cjson
You are still missing the config file /etc/orbited.cfg. It can be generated using the rails plugin or put together by hand. You should find an example in this repo.

Stomp server

Orbited provides a built-in stomp server (morbid). You can also install it separately with: sudo easy_install morbid There is a flag in the orbited configuration file to tell it start the built-in morbid server. Morbid is good enough for development and testing. For something more production-ready you should look at alternatives such as ActiveMQ, RabbitMQ, StompConnect, etc.

XMPP/Jabber as alternative to Stomp

Using an XMPP can provide some features you might find useful such as presence (know if a user is online or not) etc. There are many XMPP serves our there ejabberd being a very popular and robust implementation written in Erlang. If you want to go ahead for XMPP (i recommend going for stomp first and then switch to XMPP for the sake of simplicity):

Install ejabberd: sudo aptitude install ejabberd
Configure ejabberd
- Set the admin user/s
- Set the domains e.g. localhost
Add the users you want to use for your demo
- Example: sudo ejabberdctl register user1 localhost user1
- Syntax: sudo ejabberdctl register <username> <domain> <password>
Restart the jabber server; sudo /etc/init.d/ejabberd restart
Adapt the orbited.cfg file to allow connections to the jabber server:

[access]
- -> localhost:5222

Rails app with Orbited and Stomp

You will find a sample rails app in this repo for test and evaluation purposes. If you want to start your own rails app follow this instructions:

Install ruby and rails 2.3.5
Install the stomp gem and add it to config/environment.rb: config.gem "stomp"
Install orbited plugin: script/plugin install git://github.com/mallio/orbited
Change the config file to suit your setup: config/orbited.yml
Generate the config file for the Orbited server or write it yourself: script/generate orbited_config

Caveats

If you start the orbited server as root it will ask you for a user account to switch to after startup. In this case make sure you have a user specified in the global section of the config file like this: [global] user=<orbited_user>