What are rules in Application Streaming is well explained at eDocs , same link explains about the process of how to create File, Registry and NamedPipes rules.
I will try to explain on Why and When to use File rules. File Rules can be used for scenarios like:
1. Few Application failures with Streaming, or for faulty written applications
2. Any specific requirement to Isolate or Ignore the changes done by Streaming Environment on the file system.
Scenarios: (Hide a Folder from an App!! )
1. Let’s assume that there is an application which expects that some folder say C:\Test123 doesn’t exist on the machine, when the app is launched as well as when application is getting installed. We can solve this issue with StrictIsolate Rule on Profiler. This rule (below image) will mask the folder (present on disk) “C:\Test123″ for the installer as well as on the client when application is getting launched.
(Note: on profiler when rule is added, the change will not get effected till we save the profile)
So this way we can fool the application saying the folder doesn’t exist, regardless of it exists or not.
Scenario 2: (Isolating some settings)
For example, an application like Google Chrome stores its settings in %appdata%\Google. This can be an issue, if admin doesn’t want the settings stored by streamed application to be seen by applications running locally (non-streamed apps), but any file changes done to %appdata% by default will be saved to original disk location by streaming (by design). In this scenario Admin can set simple “Isolate” rule on the %appdata%\Google folder. So any changes written to the specific folder will be redirected to streamed cache and outside isolation apps will not see the changes done to Streamed app settings.
Scenario 3: (Ignore the files changes)
Certain folders will be isolated by default- means, any writes done by streamed application will be written to a re-directed location by Streaming Engine (without writing the changes to original location). Default isolated folders include %programfiles%, %windir%, any new folders added by 3rd party app installer. So, if admin needs “not to isolate” the changes done to any of these folder, they can add an Ignore rule to that specific folder on Profiler.
Note: Rules are advanced concept, so know what an app is doing with file system (using tools like Process Monitor) before modifying the rules.
Have fun with Streaming!