Okay so I have a cluster of pi's version 3b running up to date raspbian. I need a quick way to make changes (upload/sync) files to 20 pi's preferably on boot as I have a startup script that will launch the app but would like the newest version of the app to be run. However the boot script is run at rc.local as it need root permissions. So how can I sync files + run as root on startup? Any method will work github/dropbox/nfs/etc. (nfs will be tricky as the network is huge with many subnet so I prefer to avoid it as I am not the network manager and its a pain to get him to set things up for me) so for that reason I prefer some kind of remote file sync.
Try GlusterFS: https://blog.godatadriven.com/rpi-gluster.html
I have never tried it myself on Pi, but we are using it to connect CentOS workstations for the same purpose.