Understanding Internet Information Services - Part 2
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by Uday Denduluri
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Modes of Operation

Application isolation is the process of separating the applications from the process boundaries and also preventing one application to affect another and the reducing time that we spend on correcting the issues related to applications. IIS 6.0 operates mainly in two different application isolation modes.

·         Worker Process Isolation mode – This mode is quite new and uses the worker process core component for functioning. This mode is the default mode for the IIS 6.0 and also it is more recommended. We will see further why this mode is more robust and secure than the other mode.

·         IIS 5.0 Isolation Mode – This mode is similar to the Process model of the previous IIS version.

Let us discuss each mode in detail and also illustrate the factors on which we can choose the mode. The factors upon which we derive on a specific mode are listed below.

1.    Performance of the Application after going for a Mode

2.    Reliability of the Application (We need this especially when we go for Multi-Instancing)

3.    Security (We will discuss in next section)

4.    Some of the New cool Features

5.    Compatibility with our application (Last but not the least)

When we consider all the above factors except the last one, worker process Isolation mode is considered to be the better alternative. The only issue with it may be the compatibility issues with the legacy applications. Worker process Isolation mode is also more reliable in the security aspect. Apart from the above features, worker process isolation mode also has the support process recycling, multi instancing and the support for the application pools. Process recycling is the concept by which IIS 6.0 automates refreshing of ASP.Net web applications. By using this approach all the problematic applications are refreshed automatically and the application code modifications can be avoided. Overlapping recycling is a special case of process recycling. In this case the process which is supposed to be recycled continues to serve all the requests while another process is created in parallel. As there is an overlap between the same processes it is known as the overlapped recycling.

In this scenario we also get to see the concept of Multi instancing. Multi-instancing is the concept by which we can have 2 or more instances of the same application. In the overlapped recycling we may have the same application instances running in different processes. We have a configurable timeout field based on which we can specify the time for the process to be terminated.

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User Comments

Title: IIS   
Date: 2010-11-09 6:39:51 AM
Hi Uday ,
It was nice article,i just needed basic understanding over IIS that u explained well enough.
Title: IIS   
Date: 2009-09-20 1:56:52 PM
Hi Uday,

i have go through ur article as u have requested. The article is quite good but not perfect its looks like an article by novice be some technical it is totally incomplete missing some major issues like inetinfo, ddlhost, w3wp etc flow is not complete. it should beeeeee...if u want to contact me, mail me in makftp[at]gmail[dot]com

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