I have an existing PHP application that has run quite nicely for a while on just a single web/db server. It's gotten to the point where it needs to be broken up into servers for each service (Apache, MySQL, and batch processing). It's the batch processing that's stumped me the most. We're currently using the CodeIgniter framework for the app, so it'd be preferable to continue to use this for the batch processing (if possible), but this batch processing needs to take place on a separate server from where the front-end web application lives and runs.
I know this is kinda a broad topic, but can anyone offer any pointers? Should I be storing the code on one server, and mounting to that server from the others to access the scripts? Should I just store separate copies of the code on both batch and web servers?
The more insight or specific examples or use cases the better. I'll gladly provide more specific info if you tell me what you need to know. Thanks in advance!