Checking for file from iRule?

I am looking at implementing a downtime pool for something like 50-60 virtual servers at a time. My current idea would involve an iRule always applied to these virtual servers which as the first action checks for a file locally on the BigIP. If it exists the rule would send requests to the downtime pool, otherwise it would just exit.

 

 

This would allow us to give the application people an account, they would do a touch via a script on the file system and when the downtime is done, they would remove it.

 

 

Is this possible with iRules?