What's the best practice , using subdomains, archive SEO , keep the system scalable , and isolate the applications?

We are developing a website quite similar with ebay.com and in order to upgrade/maintain it without much effort we decided to split/isolate different parts of the website like ebay does too (e.g the item page/application will be served from cgi.domain.com , signin application from signin.domain.com, shopping cart application from offer.domain.com, search features from search.domain.com etc ). Each major application/function of the site will be deployed on a different server. Another reason for isolation the applications is the security.

I also need to mention that one application is deployed on google app engine .

However we received some "warnings" that this will affect the SEO dramatically so I have 2 questions :)

1. Is it true ? Do the subdomains decrease the pagerank of the website ?

2. If it's true how can we sort this out ? Should we use a different server which should act as a routing/proxy and make a kind of rewrite (开发者_StackOverflowe.g search.domain.com => domain.com/search etc) ?

3. What's the best practice to archive the simplicity/isolation of the applications + SEO + security + scalability in a website ?

   Thank you in advance !

Search engines no longer see sub-domains as separate sites. This was new as around Sept 2011. Whether your link-juice carries over is another thing, and it's not really explained (as of yet). Here is a reference: http://searchengineland.com/new-google-classifies-subdomains-as-internal-links-within-webmaster-tools-91401

No, multiple subdomains will not decrease page rank of the main website. However, they don't contribute to page rank either (because the search engines see them as separate sites).

However, for the sort of site that you're working on, that looks like it would be OK. For example, the only thing you really want indexed is product listings anyway - you don't need it to index login, search results and stuff like that. Also, since external websites aren't going to link to your login pages or search results either (I assume they'll only link to product pages as well) then you don't really care about those other sites contributing to your page rank.

Personally, I think people put too much focus on making sites "SEO" friendly. As long as the site is user-friendly then SEO-friendly will follow as well.