Forcing lowercase only works the first time

I think that the iRule is probably working, as this iRule is set to process everything. If you are using IIS, then it really doesn't matter because it really doesn't care, but you can still use the iRule to correct the case as it is presented to the server.

As Hoolio pointed out, it would be a resource intensive process to rewrite everything within the website, as well as the contents of the [HTTP::header "Location"] where any website Hyperlinks or Redirects would be put to transport back to the requestor.

Your best bet is going to be that the iRule is working on all incoming traffic, and then advise the developers to start using lower case for everything.

How to Verify:

 when HTTP_REQUEST {
HTTP::path [string tolower  [HTTP::path]]
log local0. "String to Lower iRule: [HTTP::path]"
}

The "log local0. "String to Lower iRule: [HTTP::path]"" will log the [HTTP::path] to the LTM Log.

Apply the iRule to a Virtual Server that you want to test.

SSH into the F5 and locate the LTM Log:

cd /var/log

Set continuous read from the LTM Log:

tail -f ltm

Do your testing and every time the iRule fires you should see the entry in the log and it should show the URL you access after it has be processed by the iRule (everything should be lower case).

NOTE: This iRule will not change the URL displayed in the Browser. It will only change what is being sent to the server.