Say I've got a web application running on a Linux VPS box. In order to apply kernel upgrades and some security fixes, I'll need to reboot the server. During this period, the server isn't reachable. I'm wondering if it's possible to display a maintenance notice to the user (via HTTP) at this time. The notice will be sent by a PHP script, which will handle requests to provide maintenance notice in either HTML format, a picture, or web service XML to clients. Or if possible, provide a partially running service.
What kinds of hardware and software do I need for this to happen (minimum budget please, and I'm hoping that a typical VPS/dedicated hosting provider can support these)?
Now I already knew that I could use software like squid to provide load balancing between 2 HTTP servers. But what do I do if squid itself needed an upgrade, or the CentOS server that's hosting squid? Plus, I don't actually need load balancing, it's fine if I have to "switch" to maintenance mode manually. Any ideas?
Thanks in advance.