Developing Web Applications in a Clustered Environment Using WLST and BEA Workshop

by Michael Meiner
07/05/2006

Abstract

A development environment typically consists of a single-server J2EE container for unit testing Web and enterprise J2EE applications. In contrast a production environment is far more likely to be a complex, clustered configuration. Problems discovered during production-level testing often require looping back to the development team for modification of the Web or enterprise application. Many of these issues can be caught earlier in the cycle by having the development team perform unit testing against a clustered environment. This tutorial presents a straightforward way for developers to try their applications in a cluster by utilizing the WebLogic Scripting Tool (WLST) to automatically provision applications into this environment.

The first part of this tutorial describes how to deploy your Web applications in a cluster using WLST. The second part adds BEA Workshop Studio into the mix, showing how to invoke the scripts created in the first part right from your development IDE.

Required Software

The following software is needed to run the samples in this tutorial. For the first part:

• WebLogic Server 9.0 or 9.1, using Custom Install to install the Web server plug-ins
• Apache HTTP Server version 2.0 or later

For the second part:

• BEA Workshop Studio 3.0 (15-day free download available) or BEA Workshop JSP Editor (free)

To use the scripts in the sample code as is, install BEA WebLogic Server using the following settings:

• BEA HOME = wls9
• PRODUCT HOME = weblogic90

Install the Apache HTTP Server using the default port 80.

Part 1: The Power of WLST

The WebLogic Scripting Tool (WLST) is a command-line scripting interface that system administrators and operators use to monitor and manage BEA WebLogic Server instances and domains. The WLST scripting environment is based on the Java scripting interpreter, Jython. In addition to WebLogic scripting functions, you can use common features of interpreted languages, including local variables, conditional variables, and flow control statements. WebLogic Server developers and administrators can extend the WebLogic scripting language to suit their environmental needs by following the Jython language syntax.

WLST has two modes: offline and online. Using WLST offline, you can create a new domain or update an existing domain without connecting to a running WebLogic Server—supporting the same functionality as the Configuration Wizard. Online, WLST provides simplified access to Managed Beans (MBeans), Java objects that provide a management interface for an underlying resource you can manage through JMX. WLST is a JMX client; All the tasks you can do using WLST online can also be done programmatically using JMX.

Let's see how you can use WLST to create a cluster and deploy an application to the cluster. Let's assume you have already developed an application (called helloApp) and successfully tested it on a single server instance. I show how you can use WLST to test the application in a cluster in three steps: create, start, and run. During the create step, you'll create the clustered domain with two managed servers. During the start step, you'll start the domain and deploy helloApp to the domain. During the run step, you'll run the application using the browser.

To get started, first you'll need to extract the WLST-scripts.zip into a directory. This tutorial assumes it's c:\wlst-workshop.

Step 1: Create

The create step involves the createcluster.py WLST script. This script first creates the Admin Server, then the managed servers, and finally the cluster.

First, create the Admin Server

Creating the Admin Server is exactly the same for a cluster as for a single server instance. I define the listen addresses (non-SSL and SSL), and then define the admin username and password (which can be used to log into the admin console).

#=========================================================
# Configure the Administration Server and SSL port.
#=========================================================
cd('Servers/AdminServer')
set('ListenAddress','')
set('ListenPort', 9001)
create('AdminServer','SSL')
cd('SSL/AdminServer')
set('Enabled', 'True')
set('ListenPort', 9002)
#=========================================================
# Define the password for user weblogic.
#=========================================================
cd('/')
cd('Security/base_domain/User/weblogic')
cmo.setPassword('weblogic')

Next, create the managed servers

The following is a portion of the script that creates the managed servers. Two managed servers are created, called ms1 and ms2. The listen ports specify the ports on which the managed servers listen for incoming traffic. In our case, these must be different since both servers will be run on the same machine. When dedicated machines are used for each managed server, the listen ports can be the same (but presumably the host, or listen address, will be different).

#=========================================================
# Create two Managed Servers and configure them.
#=========================================================
cd('/')
create('ms1', 'Server')
cd('Server/ms1')
set('ListenPort', 9101) 
set('ListenAddress', 'localhost')
cd('/')
create('ms2', 'Server')
cd('Server/ms2')
set('ListenPort', 9102)
set('ListenAddress', 'localhost')

Finally, create the cluster

You can now create the cluster, called wlsCluster, from the two managed servers, ms1 and ms2. Note that the WeblogicPluginEnabled attribute is set to true. Set this attribute to true if the cluster will receive requests from a proxy plug-in. Since you'll later be using the WebLogic Apache proxy plug-in, you do this.

#=========================================================
# Create and configure a cluster and assign the Managed Servers
# to that cluster.
#=========================================================
cd('/')
create('wlsCluster', 'Cluster')
assign('Server', 'ms1,ms2','Cluster','wlsCluster')
cd('Clusters/wlsCluster')
set('MulticastAddress', '237.0.0.101')
set('MulticastPort', 9200)
set('WeblogicPluginEnabled', 'true')

All these snippets are part of a single createcluster.py WLST script. To run it, bring up a command window, go to c:\wlst-workshop, and type:

set PATH=c:\wls9\weblogic90\common\bin;%PATH%
wlst.cmd createcluster.py myclusterdomain

Note that myclusterdomain is the name I have chosen for the domain. Look under c:\wls9\user_projects\domains\myclusterdomain to see the files in the domain.

At this point I've used WLST to create an administration server and two managed servers, and placed the managed servers into a cluster.