In SharePoint on premise, you can create multiple web applications. A web application controls security, administrative settings and URLs for your SharePoint portal. Each web app has its own domain name, authentication mechanism and set of application services. Web applications live within a IIS Site with an application pool. Once you have a web application, you can create one or more site collections and sites.
So how many web applications do you need? The basic answer should be ONE.
When we review current state SharePoint implementations, we find that some customers have created multiple web applications to segment their SharePoint farm into zones. However, this can create some significant performance impacts to your farm and to the underlying IIS server.
There is a really interesting article just published that describes the impact of creating a new web application with its own application pool, a web application added to an existing application pool or a host named site collection. In testing each of these scenarios, they tested the amount of RAM consumed by adding these new resources:
- Adding a new web application with its own application pool: 400 MB of RAM consumed
- Add a new web application to an existing application pool: 59 MB of RAM
- Add a host named site collection to an existing application pool: 2 MB of RAM
Note that these numbers reflect just starting up an empty web application with no content, no users, no load. Another article describes some more real world conditions and this is a pretty clear warning on the disadvantages of creating multiple web applications and/or application pools:
Both Steve and Spencer made a point of emphasizing that performance issues will likely be encountered even before 10 application pools is hit: “If you had 5 App pools all busy then you could easily consume 24GB+ of memory and all four cores very easily on a 64bit WFE Server”. So although 10 is the documented figure, it is neither a “magic number” nor a hard limit imposed by the software and depends largely on farm usage (think user requests and service applications, particularly resource hogs such as Performance Point).
In addition, if you move to Office 365, keep in mind that there is only one web application in your subscription and you have limited administrative control over it.