posted by jbrisbin on June 21, 2010 07:11 AM

The existing solutions for Tomcat session clustering are viable for moderate clusters and straightforward failover in traditional deployments. Several are well developed with a mature code-base, such as Apache's own multicast clustering. But there's no getting around the fact that today's cloud architectures place new and different expectations on Tomcat that didn't exist several years ago when those solutions were being written. In cloud architectures, where horizontal scalability is king, a dozen or more Tomcat instances is not unusual.

In my hybrid, private cloud, first described in my earlier post on keeping track of the availability and states of services across the cloud, I wanted to fully leverage all my running Tomcat instances on every user request. I didn't want to use sticky sessions as I wanted each request (including AJAX requests on a page) to be routed to a different application server. This is how virtual machines work at a fundamental level. Increased throughput is obtained by parallelizing as much of the work as possible and utilizing more of the available resources. I wanted the same thing for my dynamic pages. Not finding a solution in the wild, I resolved to roll my own session manager. The result is the "vcloud" (or virtual cloud) session manager. I've Apache-licensed the source code and put it on GitHub--mostly to try and elicit free help to make it better. You can find the source code here: http://github.com/jbrisbin/vcloud/tree/master/session-manager/

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posted by avanabs on June 14, 2010 10:14 AM

In recent blogs, I've been discussing a major change in the IT server applications environment, specifically the transition away from last decades JEE Application Servers and "mega-blob" applications architectures. Increasingly, we see applications being assembled, leveraging collections of services...both local and remote, sometimes even very remotely in "the cloud" (more on that in future blogs).

This time I'll be talking about planning the migration process. Perhaps the most important step when considering migration of applications from one environment to another is planning. While our temptation is typically to jump in and start coding, it is critically important to understand the objectives and benefits, assess the risks and costs, and then make the business decision. Yup, it's a "business decision", mainly because migrating a running application from one infrastructure to another affects so many areas of the IT organization, plus it can impose risks for the users. There are many successful migration projects and one common characteristic I always find is that the up front planning process was completed and socialized before launching the actual project.

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