Newsletter sign-up
View all newsletters

Enterprise Java Newsletter
Stay up to date on the latest tutorials and Java community news posted on JavaWorld

Sponsored Links

Optimize with a SATA RAID Storage Solution
Range of capacities as low as $1250 per TB. Ideal if you currently rely on servers/disks/JBODs

JavaWorld.com > Java Enterprise Edition >

J2EE clustering, Part 1

Clustering technology is crucial to good Website design; do you know the basics?

By Abraham Kang, JavaWorld.com, 02/23/01

  • Print
  • Feedback
.
Enterprises are choosing Java 2, Enterprise Edition (J2EE) to deliver their mission-critical applications over the Web. Within the J2EE framework, clusters provide mission-critical services to ensure minimal downtime and maximum scalability. A cluster is a group of application servers that transparently run your J2EE application as if it were a single entity. To scale, you should include additional machines within the cluster. To minimize downtime, make sure every component of the cluster is redundant.

In this article we will gain a foundational understanding of clustering, clustering methods, and important cluster services. Because clustering approaches vary across the industry, we will examine the benefits and drawbacks of each approach. Further, we will discuss the important cluster-related features to look for in an application server.

To apply our newly acquired clustering knowledge to the real world, we will see how HP Bluestone Total-e-Server 7.2.1, Sybase Enterprise Application Server 3.6, SilverStream Application Server 3.7, and BEA WebLogic Server 6.0 each implement clusters.

In Part 2 of this series, we will cover programming and failover strategies for clusters, as well as test our four application server products to see how they scale and failover.

Clusters defined

J2EE application server vendors define a cluster as a group of machines working together to transparently provide enterprise services (support for JNDI, EJB, JSP, HttpSession and component failover, and so on). They leave the definition purposely vague because each vendor implements clustering differently. At one end of the spectrum rest vendors who put a dispatcher in front of a group of independent machines, none of which has knowledge of the other machines in the cluster. In this scheme, the dispatcher receives an initial request from a user and replies with an HTTP redirect header to pin the client to a particular member server of the cluster. At the other end of the spectrum reside vendors who implement a federation of tightly integrated machines, with each machine totally aware of the other machines around it along with the objects on those machines.

In addition to machines, clusters can comprise redundant and failover-capable:

  • Load balancers: Single points of entry into the cluster and traffic directors to individual Web or application servers
  • Web servers
  • Gateway routers: Exit points out of an internal network
  • Multilayer switches: Packet and frame filters to ensure that each machine in the cluster receives only information pertinent to that machine
  • Firewalls: Cluster protectors from hackers by filtering port-level access to the cluster and internal network
  • SAN (Storage Area Networking) switches: Connect the application servers, Web servers, and databases to a backend storage medium; manage which physical disk to write data to; and failover
  • Databases


Regardless of how they are implemented, all clusters provide two main benefits: scalability and high availability (HA).

Scalability

Scalability refers to an application's ability to support increasing numbers of users. Clusters allow you to provide extra capacity by adding extra servers, thus ensuring scalability.

  • Print
  • Feedback

Resources