Question

Are there any criteria one should know / think about before deciding to go with 3T or 2T arch for a public website, to avoid any confusion here I’m referring to Tier as a stand alone physical server and the web browser does not count as a tier so say 3T for:

• T1- Web Server: Where you host your public front end UI, could be MVC, JSF, ASP.NET Web forms, … etc
• T2- App: Where you host your business web services SOAP, REST, etc…
• T3- DB: Your DB server, Oracle, SqlServer, etc…

Where 2T means only the web server and the DB, business is still separate but is executed in the same process running the web server.

One could argue that 3T is more scalable. That is true if we are thinking vertical but would not we achieve that scalability horizontally by throwing more Web servers instances behind a load balancer, Are there any criteria or cheat sheet one should know about, Appreciate experts input on this

If stackoverflow is not meant for these types of questions I do not know what is left? int swapping?

Answer 1

I found this blog that talks about a certain product i think but same principle holds i believe http://www.ektron.com/billcavablog/your-questions-answered-3tier-or-2tier/

The author has listed five criteria (attributes) to help make the decision:

• Security – Some organizations, such as financial institutions, have network policies that state that the forward facing website cannot communicate directly with the database. These organizations require the database to sit on a network that is unreachable from the forward facing website. In cases like this, a 3-tier architecture is a requirement because it satisfies this network policy, since the forward facing front-end website only communicates with the middle-tier and has no knowledge of any database.
• Scalability – You might be developing a marketing website that needs to be able to handle spikes in seasonal traffic. To satisfy this requirement, you may need to scale out the number of front-end machines available on short notice. Since the front-end has a very minimal Ektron footprint (no Ektron installation, few DLLs, no workarea), scaling horizontally is very simple. For example, using Amazon EC3, you can easily scale horizontally by spining up new machine instances of your front-end.
• Performance – To minimize the chattiness between the front-end and middle-tier servers in a 3-tier architecture, Ektron provides a caching layer that sits just below the Framework APIs and resides on the front-end. This layer handles the transparent storing, retrieving, and expiring of its data. Technically, this caching layer is also available in 2-tier architecture — but it’s something to keep in mind while working with 3-tier in particular, given its role in minimizing network requests to the middle-tier and improving performance.
• Availability – If you have particularly high uptime requirements, you might consider 3-tier for its ability to serve cached data from front-end memory, even in cases where the middle-tier or database are unavailable.
• Interoperability – Using 3 tier opens up the possibility of using any web application framework on the delivery tier, such as ASP.NET Web Forms (Web Application), Web Forms (Web Site), or even ASP.NET MVC. The service layer can also be consumed by any front-end application that can communicate with WCF service layer (Java, etc).