AKAMAI True-Client-IP

If you just use a new HTTP profile with no options ticked on the right hand side it is not changing any traffic as it passes through the F5. The only reason you need this profile is so the iRule has access to layer seven application traffic. Without it you cannot use the HTTP::header commands.

However using the SNAT command the way you have means you have changed the source IP address to that of the clients direct address. This means any return traffic will go directly back to the client and not the Akami server. If the client is not expecting this traffic it will be dropped so make sure that is your intention.

A better way would be to get Apache to log the specific header for you in its logs. Then you don't need an iRule, you don't even need a HTTP profile. See http://goo.gl/FxuChE for an example.