I have the following configuration of servers:

• 1 central linux server, a VPS
• 8 satellite linux servers, "crappy shared hostings"

I have a bunch of files that I need to have in all servers. Right now i'm copying them everywhere manually, but I want to be able to copy them to the central server, and then have a scheduled process that runs every now and then and synchronizes them (only outwardly, no need to try to find "new" files in the satellite servers).

There are a couple of catches though:

• I can't have any custom software in the satellite servers, or do strange command line things that'll auto connect to them and send the files directly. I know this is the way these kinds of things are normally done, but the satellite servers are crappy shared hosting ones where I have absolutely no control over anything. I need to send the files over FTP

• I also need to have, in my central server, a list of the files that are available in each of the satellite servers, to make sure they are ready before I send traffic to them.

If I were to do this manually, the steps would be:

1. get the list of files in a satellite server
2. compare to my own, and send the files that are missing
3. get the list of files again, and store it in my central database.

I'd like to know what tools are out there that can alleviate as much of this as possible, first the syncing, and then the "getting the list of files available in the other server".
I'm going to be doing everything from PHP, not sure if there are good tools to "use FTP from PHP", which i'm pretty sure i'll have to do for step 3 at least.

Thanks in advance for any ideas!
Daniel