NFRs

Description

Availability

Availability is improved due to the separation of the web servers from the rest of the system software: a web server can fail without having an adverse impact on any particular application software instance.

Performance

Performance can be improved depending on the degree to which the web and application/data hardware servers can be optimized. This relies on the type of application and its interface: sites with lots of graphics or large binary assets to be downloaded, or particularly complex application functionality, are likely to benefit most from the split.

Scalability

Scalability is improved due to the ability to scale the web server and application server load-balanced pools independently.

Security

Security is negatively impacted as there are now a number of new elements that need to be secured. However, dedicated web and application servers does provide the foundation for the demilitarized zone security pattern.

Manageability

Manageability is negatively impacted due to the need to separately manage the web servers and application servers, plus the additional load balancers.

Maintainability

Maintainability is potentially improved as problems unique to the web servers can be isolated on those machines. Equally, the web servers and the application server stack can be fixed independently if necessary.

Flexibility

Not affected.

Portability

Not affected.

Cost

The introduction of a number of new hardware servers may initially have a negative impact on cost, depending on the size of the servers required. However, the use of optimized or specialist hardware should prove cheaper in the long run: scaling the system doesn't necessarily require new hardware of all types to be purchased.