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My general take on this sort of scenario is first to eliminate all the redundant hostnames with round-robin DNS, through adding extra server power with software-based load-balancing in the interim with a solution like InterWorx, and breaking out database servers.   If you do that, you should have a nice little server cluster that's crazy efficient.and scalable.  You can add a CDN to the mix if you like as well.  With all of that, SEO should work the same way as on a single server. Sitemaps can then be generated dynamically really easily (in under 25 lines of code, most of the time). If you just want a way to mirror static files, you'll want to look at rsync. And finally, as for S3, my personal opinion is to stay away.  I'm an SEO, but I also spent 7 years building a hosting company.  Those solutions sound great in their marketing, but are scientifically less reliable than standard hosting, and you can verify that via public uptime tracking sites like HyperSpin.

Hi Éber, In my opinion, it's totally legitimate to nofollow those links to your login page, assuming they are showing the same 302 redirect and login page to Google. This will cut down on excessive crawling and possibly help you out with your Google Crawl "allowance." If, on the other hand, you wanted to direct some link juice towards your login page, you could turn the 302 into a 301. There might be other solutions, such as blocking the page with robots.txt, or using clever javascript. That said, nofollow is probably the easiest.