Managing Websites with IIS Manager (part 2) - Understanding Application Pools

2. Understanding Application Pools

One of the slightly unusual details of website management is that some settings are set on the website itself (on the virtual directory), while others are applied through a feature called application pools. This two-part design allows for more efficient management, because you don't need to duplicate the application pool settings (which very rarely need to be changed) for each new web application. Instead, you can reuse a single application pool for all your websites. And if you modify the application pool later, all the linked web applications are affected.

Before you examine how to create and change application pools, you need to understand that application pools are quite limited in scope. Most web application configuration is performed through the virtual directory. The web application pool sets a small group of low-level settings that apply only to ASP.NET applications, such as the maximum number of requests to put on hold before sending a "Service Unavailable" response to new clients (by default, it's 1000) and the number of times the website should be allowed to crash catastrophically before being shut down altogether (by default, 5). Although these settings are interesting, most shouldn't be touched by anyone but a seasoned network administrator. In most cases, the default values are the best bet.

However, application pools include two settings that are uniquely important and may require your customization:

• The version of ASP.NET that IIS runs to process the requests in your website

• The Windows account that IIS uses to run your website

To take a look at the application pools defined on your computer, expand the IIS Manager tree, and click the Application Pools item that's nested under your computer name, before the Sites group (Figure 3).

Figure 3. The standard application pools

When you first install IIS, you start with a couple of basic application pools named DefaultAppPool and Classic .NET AppPool. When you install ASP.NET, the installation program creates two more IIS application pools—ASP.NET v4.0 and ASP.NET v4.0 Classic.

When you look at the application pool list, you can quickly pick out several details, such as the version of .NET that the application pool uses, whether it runs in classic mode or the more modern integrated mode, and how many applications are currently assigned to that pool. For example, in Figure 3, one application is assigned to the ASP.NET v4.0 pool, while the other pools have no web applications at all.

Here's a quick rundown of the essential tasks you can perform when viewing application pools in IIS Manager:

Change basic settings for a pool:

Select the pool, and click Basic Settings in the Actions pane on the right. The basic settings let you change just three details (see Figure 4). These are the version of .NET, whether the pool uses classic or integrated mode, and whether the pool starts automatically when the computer boots up (so as to prevent an unnecessary delay when the web server receives the first request for your website).

Change advanced settings for a pool:

Select the pool, and click Advanced Settings in the Actions pane on the right. The Advanced Settings window appears, with a property grid of options. You'll use the Advanced Settings window to change the application pool account in the next section.

Create a new pool:

Click Add Application Pool in the Actions pane. This is the best approach if you want to create a pool with new, customized settings (such as a different Windows account). That way, you can keep your application pool separate from the standard, default pools. This also makes sense if you want some applications to use your pool and the rest to use one of the standard pools.

See what applications are in a pool:

Select the pool, and click View Applications in the Actions pane. This way, you'll know what websites will be affected if you decide to tweak application pool settings.

Figure 4. Basic application pool settings