automagically cluster Lift web sessions with Terracotta

Lift Web Framework Is a MVC Framework written in Scala, Which are two things I know exactly nothing about. Being that, I thought It would be a good example to show how easy it is to cluster web session using terracotta new express web session product. Here's a link to our Beta ...

Part 1: The Lift/Scala Thing...

So first I had to figure out what the deal with Lift is about. Good thing there's a fairly simple tutorial to create a basic HelloWorld lift webapp here. First let's download and install all the bits you need to write a Lift web app, fortunately for me it was just the Scala Eclipse Plugin.

Let us create a maven project:


mvn archetype:generate -U \
-DarchetypeGroupId=net.liftweb \
-DarchetypeArtifactId=lift-archetype-blank \
-DarchetypeVersion=1.0 \
-DremoteRepositories=http://scala-tools.org/repo-releases \
-DgroupId=com.examples.terracotta \
-DartifactId=clusteredCounter \
-Dversion=1.0-SNAPSHOT

cd clusteredCounter
mvn jetty:run

Now you got yourself a fully functioning hello world webapp. Let's add some code where we are actually saving and displaying session data.

add a Lift Snippet that would process url parameters add then to the session and then display all the session attributes:


package com.examples.terracotta.snippet

import javax.servlet.http._
import net.liftweb.http._
import net.liftweb.util._
import net.liftweb.util.Helpers._

import net.liftweb.http.SessionVar
import scala.collection.mutable.HashMap
import scala.xml._
import java.util.Enumeration
import scala.collection.mutable.HashSet

class ViewSubmission {


def showStuff : NodeSeq = {

var title = S.param("title").openOr("")
var url = S.param("url").openOr("")

S.servletSession.get.setAttribute(title, url)

var e = S.servletSession.get.getAttributeNames
val names = new HashSet[String]
while (e.hasMoreElements()) {
val name = e.nextElement().asInstanceOf[String]
names += name
println(names)
}

<table> {
for (name <- names) yield
<tr>
<td>Title</td>
<td>{name}</td>
</tr>
<tr>
<td>Url</td>
<td>{S.servletSession.get.getAttribute(name)}</td>
</tr>
}</table>

}

}

Edit the index.html to show edit and show session data:


<lift:surround with="default" at="content">
<table>
<lift:snippet type="viewSubmission:showStuff" />
</table>
<form>
<tr>
<td>Title</td>
<td>
<input type="text" name="title" />
</td>
</tr>
<tr>
<td>Url</td>
<td>
<input type="text" name="url"/>
</td>
</tr>
<tr>
<td>&nbsp;</td>
<td><input type="submit" value="Add" /></td>
</tr>
</form>
</lift:surround>


Run mvn -Djetty.port=9999 jetty:run and another instance with

mvn -Djetty.port=9999 jetty:run. got to http://localhost:8888 and http://localhost:9999. you can only see the data you added to each local web session.

Now the fun part...

Part 2: Clustering the web session

First we need to add our express web session jar to the pom.xml as a dependency:


<dependency>
<groupid>org.terracotta.session</groupid>
<artifactid>terracotta-session</artifactid>
<version>1.1.0-SNAPSHOT</version>
</dependency>

and also Terracotta Maven Repo information..

<repository>
<id>terracotta-snapshots</id>
<url>http://www.terracotta.org/download/reflector/maven2</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>


Let us add our terracotta filter for clustering:


<filter>
<filter-name>terracotta</filter-name>
<display-name>Terracotta Session Filter</display-name>
<!-- The filter class is specific to the application server. -->
<filter-class>org.terracotta.session.TerracottaJetty61xSessionFilter</filter-class>
<init-param>
<param-name>tcConfigUrl</param-name>
<!--
<param-value> of type tcConfigUrl has a <param-value> containing the
URL or filepath (for example, /lib/tc-config.xml) to tc-config.xml.
-->
<param-value>localhost:9510</param-value>
</init-param>
</filter>

<filter-mapping>
<filter-name>terracotta</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>




Now start our terracotta server, download here

Start are terracotta server and then run the jetty servers again. this time you can see session data on entered in on one server appear on the other.

Example Project