Is there anyway to broadcast a message to everyone on my server in an event of a reboot of the server so they will know whats going on...I mean reboots may only occur once in a great while(updates etc) I know you can do so in windows but what about centOS?
In theory you could redirect all apache requests to single page that would have notice about upcoming reboot but I see no reason to do so as while the server is down it too would be down so noone would see it. You should probably look into DNS based redirect (something along lines of having 3rd name server that would point to alternate location while first 2 name servers are not responding)
Unless your TTL is like 5 seconds the setup you're proposing would be completely useless. The clients would still be using the "old" IP address, that is to say, the one of the rebooting machine. If you can't take a reboot in terms of downtime, load balance and setup high availability.
Traditionally you don't display "server down" on customer webpages when the server is down. You just make sure you manage it competently so it doesn't go down for too long.
Agreed. Putting that on a client website would cause more harm than good, especially if their clients see the site and it goes back to the primary client (owner of the site, who comes to you and flips out, especially if you're running any e-commerce elements where monetary loss is concerned). Plus, if your server is in the process of being rebooted, the client won't see it anyway. You don't want to cause any more site downtime than the reboot requires, so replacing their main page with "We will be down for 2 hours tonight" is just not common sense.
If you're scheduling downtime, you should email your clients in advance and let them know the window of downtime (to follow business etiquette). If your reboot is short, then you really don't have to email your clients. (If I emailed my clients every time I rebooted the server for a kernel patch, they would be disappointed about server stability. Fortunately, our servers are back up within 2 minutes.)