Architecture Review

Most modern implementation of client-server applications today, are built on an n-tier architecture. The classic n-tier architecture is built on three layers; the webserver, the application server, and the database server. Depending on a number of factors, there may be one server that is both a webserver and an application server. In other cases, there may be a separate webserver and application server. There can also be multiple servers on any layer of the architecture.

Webserver Layer:
The Webserver tier is typically the first tier of servers that aren't part of a front-end security and network infrastructure. Our experience typically shows a Sun Netra T1 AC200, or similar server, at this tier. Certainly there are many factors which should influence the decision about why type of server to place in this layer. For example, will you be serving up a lot of static content? Then you might want to consider a server capable of holding significant (2G or more) of RAM for caching your content in memory, reducing the need for frequent and expensive disk access.
If you are performing any business logic or executing application code
on this layer, you'll probably be interested in additional CPU capacity.

Application Server Tier:
This is the layer where the majority of Business Logic resides. How is data collected? What does it mean? Where is it going? How will it get there? Decisions about your data are generally made here. The brains
of the operation. Chackett Consulting has experience with several major Application Servers including Blue Martini, BroadVision, BEA Weblogic, and iPlanet. We have the broad infrastructure knowledge to provide useful insight regardless of the specific application server used here.

Database Layer:
Our primary area of expertiese here is with Oracle. Chackett Consulting has been involved in projects with other DB providers such as Informix, but the bulk of our engagements involve Oracle at this layer. The unique characteristics of this tier in the infrastructure make it one of the more important when considering hardware and network requirements.
Without implementing something like Oracle Parallel Server, this tier is VERY difficult and expensive to scale horizontally. Which means it's a good idea to do careful capacity planning on this tier right from the start.

The n-th Tier?
What exactly is the nth tier? Well in our experience the most common nth tier is load balancing. We have seen this done primarily with Cisco, f5 Networks BigIP machine, or a dedicated Intel or other chipset appliance. The goal of a good load balancer is to direct traffic across a horizontally scaled tier of the architecture (most often the webserver tier). The BigIP machine from f5 Networks seems to be a great solution here. Based on the BSD Unix OS, it is flexible, fast, and easy to set up and configure. There are so many issues to consider when implementing an n-tier application infrastructure that it's hard to feel comfortable that you have considered everything. From load balancers, security concerns, redundancy, and fault tolerance, it would be impossible to identify every potential concern, but utilizing an organization like Chackett Consulting, can help put your mind at rest that your infrastructure has been reviewed by an objective, knowledgeable, third party.