Project: juggernaut-kafka - The Ruby Toolbox

#Juggernaut

This is a forked and modified version of original Juggernaut. Instead of Redis this version uses Apache Kafka - a high-throughput distributed messaging system written and outsourced by Linkedin. My concern was that although Redis is blazing fast it is unclear how to distribute it at the point when one server won't be enough. Kafka is easily distributed and seems like a better solution for scalable real-time notification system.

Juggernaut gives you a realtime connection between your servers and client browsers. You can literally push data to clients using your web application, which lets you do awesome things like multiplayer gaming, chat, group collaboration and more.

Juggernaut is built on top of Node.js and is super simple and easy to get going.

##Features

Node.js server
Ruby client
Supports the following protocols:
- WebSocket
- Adobe Flash Socket
- ActiveX HTMLFile (IE)
- Server-Sent Events (Opera)
- XHR with multipart encoding
- XHR with long-polling
Horizontal scaling
Reconnection support
SSL support

As you can see, Juggernaut supports a variety of protocols. If one isn't supported by a client, Juggernaut will fallback to one that is.

Supported browsers are:

Desktop
- Internet Explorer >= 5.5
- Safari >= 3
- Google Chrome >= 4
- Firefox >= 3
- Opera 10.61
Mobile
- iPhone Safari
- iPad Safari
- Android WebKit
- WebOs WebKit

##Requirements

Node.js
Apache Kafka
Ruby (optional)

##Setup

###Install Node.js

If you're using the Brew package management system, use that:

brew install node

Or follow the Node build instructions

###Install Apache Kafka

Installing Kafka is almost as easy as installing Redis.
Follow Kafka quickstart instructions

###Install Juggernaut

Juggernaut is distributed by npm, you'll need to install that first if you haven't already.

npm install -g juggernaut-kafka

###Install the Juggernaut client gem

This step is optional, but if you're planning on using Juggernaut with Ruby, you'll need the gem.

gem install juggernaut-kafka

##Running

Start ZooKeeper:

bin/zookeeper-server-start.sh config/zookeeper.properties

Start Kafka server:

bin/kafka-server-start.sh config/server.properties

Start Juggernaut:

juggernaut

That's it! Now go to http://localhost:8080 to see Juggernaut in action.

##Basic usage

Everything in Juggernaut is done within the context of a channel. JavaScript clients can subscribe to a channel which your server can publish to. First, we need to include Juggernaut's application.js file. By default, Juggernaut is hosted on port 8080 - so we can just link to the file there.

<script src="http://localhost:8080/application.js" type="text/javascript" charset="utf-8"></script>

We then need to instantiate the Juggernaut object and subscribe to the channel. As you can see, subscribe takes two arguments, the channel name and a callback.

<script type="text/javascript" charset="utf-8">
  var jug = new Juggernaut;
  jug.subscribe("channel1", function(data){
    console.log("Got data: " + data);
  });
</script>

That's it for the client side. Now, to publish to the channel we'll write some Ruby:

require "juggernaut"
Juggernaut.publish("channel1", "Some data")

You should see the data we sent appear instantly in the open browser window. As well as strings, we can even pass objects, like so:

Juggernaut.publish("channel1", {:some => "data"})

The publish method also takes an array of channels, in case you want to send a message to multiple channels co-currently.

Juggernaut.publish(["channel1", "channel2"], ["foo", "bar"])

That's pretty much the gist of it, the two methods - publish and subscribe. Couldn't be easier than that!

##Flash

Adobe Flash is optional, but it's the default fallback for a lot of browsers until WebSockets are supported. However, Flash needs a XML policy file to be served from port 843, which is restricted. You'll need to run Juggernaut with root privileges in order to open that port.

sudo juggernaut

You'll also need to specify the location of WebSocketMain.swf. Either copy this file (from Juggernaut's public directory) to the root public directory of your application, or specify it's location before instantiating Juggernaut:

window.WEB_SOCKET_SWF_LOCATION = "http://juggaddress:8080/WebSocketMain.swf"

As I mentioned above, using Flash with Juggernaut is optional - you don't have to run the server with root privileges. If Flash isn't available, Juggernaut will use WebSockets (the default), Comet or polling.

##SSL

Juggernaut has SSL support! To activate, just put create a folder called 'keys' in the 'juggernaut' directory, containing your privatekey.pem and certificate.pem files.

>> mkdir keys
>> cd keys
>> openssl genrsa -out privatekey.pem 1024 
>> openssl req -new -key privatekey.pem -out certrequest.csr 
>> openssl x509 -req -in certrequest.csr -signkey privatekey.pem -out certificate.pem

Then, pass the secure option when instantiating Juggernaut in JavaScript:

var juggernaut = new Juggernaut({secure: true})

All Juggernaut's communication will now be encrypted by SSL.

##Scaling

Scaling is just a case of starting up more Juggernaut Node servers, all sharing the same Kafka cluster. Put a TCP load balancer in front them, distribute clients with a Round Robin approach, and use sticky sessions.

It's worth noting that the latest WebSocket specification breaks support for a lot of HTTP load balancers, so it's safer just using a TCP one.

##Client Events

Juggernaut's JavaScript client has a few events that you can bind to:

connect
disconnect
reconnect

Juggernaut also triggers data events in the context of an channel. You can bind to that event by just passing a callback to the subscribe function. Here's an example of event binding. We're using jQuery UI to show a popup when the client loses their connection to our server.

var jug = new Juggernaut;

var offline = $("<div></div>")
  .html("The connection has been disconnected! <br /> " + 
        "Please go back online to use this service.")
  .dialog({
    autoOpen: false,
    modal:    true,
    width:    330,
    resizable: false,
    closeOnEscape: false,
    title: "Connection"
  });

jug.on("connect", function(){ 
  offline.dialog("close");
});

jug.on("disconnect", function(){ 
  offline.dialog("open");
});

// Once we call subscribe, Juggernaut tries to connnect.
jug.subscribe("channel1", function(data){
  console.log("Got data: " + data);
});

##Excluding certain clients

It's a common use case to send messages to every client, except one. For example, this is a common chat scenario:

User creates chat message
User's client appends the message to the chat log, so the user sees it instantly
User's client sends an AJAX request to the server, notifying it of the new chat message
The server then publishes the chat message to all relevant clients

Now, the issue above is if the server publishes the chat message back to the original client. In which case, it would get duplicated in the chat logs (as it already been created). We can resolve this issue by recording the client's Juggernaut ID, and then passing it as an :except option when Juggernaut publishes.

You can pass the Juggernaut session ID along with any AJAX requests by hooking into beforeSend, which is triggered by jQuery before sending any AJAX requests. The callback is passed an XMLHttpRequest, which we can use to set a custom header specifying the session ID.

var jug = new Juggernaut;

jQuery.beforeSend(function(xhr){
  xhr.setRequestHeader("X-Session-ID", jug.sessionID);
});

Now, when we publish to a channel, we can pass the :except option, with the current client's session ID.

Juggernaut.publish(
  "/chat",
  params[:body],
  :except => request.headers["X-Session-ID"]
)

Now, the original client won't get the duplicated chat message, even if it's subscribed to the /chat channel.

##Server Events

When a client connects & disconnects, Juggernaut triggers a callback. You can listen to these callbacks from the Ruby client,

Juggernaut.subscribe do |event, data|
  # Use event/data
end

The event is either :subscribe or :unsubscribe. The data variable is just a hash of the client details:

{"channel" => "channel1", "session_id" => "1822913980577141", "meta" => "foo"}

##Metadata

You'll notice there's a meta attribute in the server event example above. Juggernaut lets you attach meta data to the client object, which gets passed along to any server events. For example, you could set User ID meta data - then you would know which user was subscribing/unsubscribing to channels. You could use this information to build a live Roster of online users.

var jug = new Juggernaut;
jug.meta = {user_id: 1};

##Using Juggernaut from Node.js

We can use a Node.js Kafka adapter to publish to Juggernaut.

var kafka   = require("kafka");

var msg = {
  "channels": ["channel1"],
  "data": "foo"
};

var producer = new kafka.Producer({
  // these are also the default values
  host:         'localhost',
  port:         9092,
  topic:        'juggernaut',
  partition:    0
})

producer.connect(function() {
    producer.send(msg)
})

juggernaut-kafka

Runtime