Deprecated - Performance and scalability

How to make Drupal run on a HA cluster? This is what we are working on.

Drupal is installed on an NFS share, and runs on several apache nodes, were all accesses Drupal files on the NFS. The database is an MySQL cluster. There is a load-balancer distributing in the front the load between the apache nodes. I have just installed the systems and more information to come as we progress.

I forsee lots of funny bugs :-)

I've been using Drupal for a while now and have had to use some duct tape style hacks to get things working well. One of them was using file caches for specific high-volume pages that aren't modified often and then redirecting those pages via htaccess. For example, I have a page of applications, with a url alias of example.com/applications. This is a heavily used page that is only modified once every few weeks. So, I pull the page as an anonymous user and save it in a cache directory on the server as applications.html. Then within .htacess, I redirect it to this file using the following:
RewriteRule ^applications$ http://example.com/cache/applications.html [L]

This reduced the load on the server quite a bit. It's still struggling badly under load, but it's better. The main reason I had to do this is that I have lots of users (15,000+) and most of them are logged in all the time... making the Drupal cache mostly useless with them. But, this got me thinking... wouldn't it make sense to be able to set specific pages within a Drupal site to treat ALL users as anonymous, thus being able to better utilize Drupal's cache? Or, perhaps, all users except those of a specific type (say 'admin' users)?

I know editing would be an issue (how would Drupal display the Edit tab?)... so just showing it for specific types of users would work. Any thoughts on this?

Everything was fine since a couple of weeks ago and i can't recall what i have changed or what happened.
Usually people who are subscribed to a group will automatically receive a notification of new content. Since a couple of weeks they are not getting content but the 'vars' instead. What could cause this problem?

%type '%subject' by %username

%body

View original: %content_url
Post reply: %reply_url

--
You are subscribed to the group '%group' at '%site'.
To manage your subscription, visit %group_url

In short,

I would like to create a page/node that displays all recent posts in a brief news RSS style scrolling Upwards with View links.

I would like the processing part to be done server side in the background so as to minimize slowness when generating the page list.

I had my site (4.7+) hosted on site5 shared hosting some while back. They kept blocking my site saying I was using too many resources. Decided to move to MediaTemple Grid Server account a few months back. Same thing there, was getting charged over the monthly fee for using excessive amounts of resources. My site has about 50+ people (guest + members) on it any given time, recently it has hit 100, but for relatively short period of time.

The modules running on the site are not know to be resource hogs, fairly standard, partial list below:

I'm considering loading my comment table (200mb) onto a ramdisk to speed up read access and was wondering if anyone has had any experience with doing this. Does it really increase performance? What about reliability?