Can I Replace Apache with Node.js?

I have a website running on CentOS using the usual suspects (Apache, MySQL, and PHP). Since the time this website was originally launched, it has evolved quite a bit and now I'd like to do fancier things with it—namely real-time notifications. From what I've read, Apache handles this poorly. I'm wondering if I can replace just Apache with Node.js (so instead of "LAMP" it would "LNMP").

I've tried searching online for a solution, but haven't found one. If I'm correctly interpreting the things that I've read, it seems that most people are saying that Node.js can replace both Apache and PHP together. I have a lot of existing PHP code, though, so I'd prefer to keep it.

In case it's not already obvious, I'm pretty confused and could use some enlightenment. Thanks very much!

PHP Warning: Unknown: failed to open stream

I edited the apache httpd.conf file recently for the mod_rewrite to work. I don't know if this problem originated from that or not, but i'm getting this problem from that day.
This is what I see on the frontend when I run the software -

Server error The website encountered an error while retrieving http://localhost/prestashop/. It may be down for maintenance or configured incorrectly.

There is no specific file that triggers this. But I saw that usually small programs that consists of 4-5 php files, runs fine, but softwares with a lot of files(like PrestaShop) don't.
I checked the logs and this is what I found.

[Wed Mar 16 19:33:39 2011] [error] [client ::1] PHP Warning:  Unknown: failed to open stream: Permission denied in Unknown on line 0
[Wed Mar 16 19:33:39 2011] [error] [client ::1] PHP Fatal error:  Unknown: Failed opening required '/var/www/html/yomig/index.php' (include_path='.:/usr/share/pear:/usr/share/php') in Unknown on line 0
[Wed Mar 16 19:33:39 2011] [error] [client ::1] File does not exist: /var/www/html/favicon.ico
[Wed Mar 16 19:33:41 2011] [error] [client ::1] PHP Warning:  Unknown: failed to open stream: Permission denied in Unknown on line 0
[Wed Mar 16 19:33:41 2011] [error] [client ::1] PHP Fatal error:  Unknown: Failed opening required '/var/www/html/yomig/index.php' (include_path='.:/usr/share/pear:/usr/share/php') in Unknown on line 0

Apache mod_cache: Vary cache based on cookie values

Currently, I am using mod_cache to cache the page details of a web application.

I have the cache Vary based on User-Agent and Accept-Language, since there are different payloads for those situations.

Vary: User-Agent, Accept-Language

We have plans to have region-specific information on each page, but this is where we are trying to determine our caching strategy.

We have a cookie that persists to indicate the region we geolocated for, but obviously the cache does not vary based on this cookie.

It is possible to vary based on the value for certain cookies or headers in general? (Note I say certain cookies, as we wouldn't want the session identifier to collide with this) - something like a regex match to this:

location=(.+?);