I have run various configuration trying to achieve this and what I found to work best was.
- Intel 7115 hardware SSL (ebay $300)
- Cisco/Arrowpoint load balancer (ebay $500)
- Sun v100 web servers (sun $1000)
- Sun ?? database server (sun >6000)
- Oracle $$$
I prefer Sun hardware (for remote management) but Linux would work fine. The problem is the only place you'll save any money is the database server and that should really be a 64bit box if your database is more than a few gig. Plus the database server is not the place to cut corners. 64bit Linux may be too new to be considered high-availability. You'll need at least 6 webservers and 2 of everything else. Hardware cost > $20,000.
I used Oracle standby server to replicate the data to a warm duplicate setup in a separate data center. Making the switch to the backup data center was a manual process. In theory it's not that hard. We never had to do it for real. You might be able to do this with Postgresql now.
Access and Error logs are copied back to separate machine every day
I had one machine dedicated to scheduled tasks. It was the only one that sent email, plus various other things. If that machine failed it was a manual process to designate another as master.
Oracle standby in 9i is pretty good. Unfortunately because ACS uses index organized tables you lose the read-only functionality
With the load balancers you can do upgrades to each web server without taking the site offline. This works well for small incremental releases. Large upgrades might be different. It took 48 hours to an 8i to 9i upgrade mostly because of import/export time.
The database server is the weakest link. Not because it's unreliable but because it's central to the process and difficult to have backups. 10g rac on 64bit Linux might change that.
In short cheap front end stuff (ssl, load balacers, webservers ) and have a bunch of them. Don't worry about dual power supplies, raid drives etc. have whole spare boxes. Put your money in the database server with dual supplies, raid etc.
