I've been reading about full redundancy to achieve almost if not 100% uptime for your mission critical applications (handling financial data) running in a dedicated server, but I still can't wrap my head on how I could do this.
1) Let's say I have multiple web apps (with large and frequent files and DB updates) running in my current server. From what I read I would need to get another dedicated server (as a backup server) where I could mirror in all the files and DB data, and if my primary server went down for any reason my backup server would carry the load immediately. The transfer from primary server to backup server is done through DNS. Is this correct? Is there a more better way to achieve redundancy than this?
2) If we did the what I mentioned in #1, what would happen if the primary server went online again? How would the primary server catch up from all the changes done on the backup server?
3) Is there a definite guide out there I could read on the best way I could do this? I've searched through Google already but what I mostly encounter would not work for us because our web apps can't be down for more than 5 minutes at least and we can't lose 5 minutes worth of data.
4) Is there a service out there that could do this for us? Since we already have an existing dedicated server, the service would have to work around existing working environment. But I would prefer if I could learn how I could do this myself.
I would greatly appreciate it if you guys could point me to the right direction here.