Fedora is unstable in that you have to take down your site every six months to upgrade to the next supported release, or you lose access to bug fixes and thus your site becomes vulnerable to attack by hackers. Whereas with Centos, you do 'yum update' every so often and only need to reboot if the kernel changed and if the kernel changed in a way that matters to you. (If some obscure function changed that I don't use, obviously I don't need to reboot). I've had Centos systems up and running serving code continually for two years straight, interrupted only by a power outage that took down the host ESXi server. I've never had an outage more than a minute due to an update from one minor version of Centos to the next minor version of Centos. Meanwhile, Fedora requires an outage of close to an hour with each update.