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Developing Web Applications in a Clustered Environment Using WLST and Workshop

Developing Web Applications in a Clustered Environment Using WLST and Workshop

Now select wlst-createcluster in the left panel, as shown in Figure 6.

Figure 6: Looking at wlst-createcluster in External Tools

This screen specifies the name of the program to run (wlst.cmd), the Working Directory (wlst-workshop), and the arguments that will be passed to WLST (createcluster.py and myclusterdomain). The first argument passed to WLST is always the name of the script; subsequent argument(s) represent any inputs the script expects. In this case, the createcluster.py script expects the name of the domain, which I've named myclusterdomain. Click on the Run button at the bottom of the screen to create the domain.

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

Step 2: Start
In this step you start the clustered domain and then deploy the application to the cluster. These steps are analogous to those described in Part 1.

To start the cluster, select the program called wlst-startcluster in the External Tools panel. This will invoke the same script that ran in Part 1.

Similarly, to start the application first click on hello.html and bring it up in the main window. This will ensure that the right application is deployed. Then, select the program called wlst-deploy in the External Tools panel. This will invoke the deploy.py script, which deploys the helloApp application to the cluster.

In each case, you may need to adjust the parameters on the External Tools screen if you are not using the defaults. Note that the last parameter in the deploy arguments is http://localhost/hello.html. This will automatically invoke the browser with this URL. You can change this depending on your settings if not using the HTTP Server with port 80. At this point you've used WLST and Workshop to start the cluster and deploy the application to the cluster. Let's now run it!

Step 3: Run
Running the application is again identical to Part 1—just enter the appropriate URL into your browser (or use the browser that was invoked at the end of Step 2). Using Apache as a load balancer, type: http://localhost/hello.html.

Type in your name and click on Submit. Now, let's run the getstatus.py command from External Tools. This will tell you which server (ms1 or ms2) is serving the requests. Now, hit refresh on the browser, and then run getstatus again. Notice that the same server is invoked, using the same session.

Now, let's see what happens if one of your servers goes down. Let's kill the server (ms1 or ms2) that is serving these requests. To kill it, use the stopserver.py command from External Tools. Make sure to change ms1 to ms2 in the arguments window if you need to stop ms2. Now, hit the refresh button again. Notice two things:

  1. The request is now served by the other managed server (as can be observed by running the getstatus script).
  2. The session ID has changed!

The first behavior is desirable, as clustering is designed to enable high availability; in the event of a server crash, another server in the cluster should pick up the load. However, the second behavior may not be desirable, as you may expect the surviving managed server to use the same session as was used by the first server. This is what is known as session replication. So what happened here?

What you need to do is configure the application to use session persistence. Bring up the helloApp application in Workshop, and edit the weblogic.xml file, which is located under the WEB-INF directory. You need to add the following snippet to enable session replication:

<session-descriptor>
<persistent-store-type>replicated</persistent-store-type>
</session-descriptor>

The default setting (persistent store type of memory) does not replicate session across clustered servers. Setting the parameter above to replicated allows sessions to be replicated across servers in a cluster. Therefore, when the managed server serving the session goes down, the surviving server takes over the sessions. The end user continues working as if there was no system failure.

Now, restart the failed managed server by running wlst-startserver from External Tools, and then redeploy helloApp by executing wlst-redeploy.

Now, retry the above experiment. You'll see that when the surviving server takes over, it uses the same session ID!

You've now used Workshop with WLST to create a fully functional clustered environment for testing the application. You can now iteratively make changes to the application, redeploy the application to the cluster, and test. The Workshop and the WLST scripts provided here do all the hard work, so you as a developer can focus on your application and quite easily test in a clustered environment.

The Big Picture
In this article I focused on developer productivity, and in particular, how developers can test their applications in a clustered environment, facilitating easy testing. Once the developer has completed the development phase (with sufficient unit/cluster testing), the application is typically handed off to other teams for different stages, such as: integration, QA/staging, and production. WLST can also be leveraged in these stages to automate domain and application provisioning and further reduce the time required to deliver the application into production. For more information on how WLST can be leveraged in these stages, see Automating WebLogic Platform Application Provisioning: A Case Study (Dev2Dev, August 2005).

Conclusion
As applications move through the lifecycle stages from development to production, the environments become increasing more complex at each stage. One such area of complexity is clustering. Since developers typically test exclusively in a single-server environment, the chances of encountering problems in later stages is increased. By providing the means for developers to try their applications in a cluster with minimal overhead, many of these problems can be fixed early in the lifecycle of the project.

This tutorial presented the means for developers to run their applications in a clustered domain. By leveraging the power of WLST and Workshop, I was able to show how developers can create, deploy, and start their applications right from the same environment they use to develop and run the application on a single-server domain. Giving this power to developers will shorten the project life cycle and enable projects to be more rapidly deployed into production.

Download
The sample code used in this article can be downloaded here.

Resources

  • WLST Project home on CodeShare - Scripts and utilities using WLST Offline and/or WLST Online
  • WLST Command and Variable Reference (product documentation) - Description of WLST commands and variables in details
  • Dev2Dev's BEA Workshop Product Center - for related material and downloads
  • Understanding Cluster Configuration and Application Deployment (product documentation) - information that defines how the configuration of a cluster is stored and maintained
  • Failover and Replication in a Cluster (product documentation) - how WebLogic Server detects failures in a cluster, and how failover is accomplished
  • Using Node Manager to Control Servers (product documentation) - describes Node Manager functionality, architecture, and configuration procedures
  • Apache HTTP Server - a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards
  • WebLogic Apache HTTP Plug-in ( product documentation) - describes how to install and configure the Apache HTTP Server Plug-In
  • Automating WebLogic Platform Application Provisioning: A Case Study by Andy Lin, showing more complex provisioning scenarios (Dev2Dev, August 2005)
  • More Stories By Michael Meiner

    Michael Meiner is an Engineering Director at Oracle Corporation. His organization is responsible for lifecycle Quality Assurance of the Fusion Middleware Suite of products, including: installation, configuration, upgrade, test-to-production and interoperability on a range of computing platforms and Operating Systems. The Fusion Middleware product suite supports both On-Premise as well as Cloud offerings.

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