A few basic questions

[David Miller]

Hi All;

The company I work for is moving to a drupal content management system.  
We expect to install a caching reverse proxy between the drupal servers 
and the Internet.  I'm looking into nginx and varnish for that role.

There's no question nginx provides for at least a basic high-speed 
caching reverse proxy, but I'd appreciate input from people using it 
with regards to these features:

1) Flexible health-checks of back-end web servers.  Can I configure 
nginx to accept a 503, for example, as an acceptable return code?  Can I 
specify a different health-check page for each back-end server?

2) Flexibility in load balancing.  Can I specify anything other than 
round-robin?  Least connections, lowest load, that sort of thing?

3) Ability to purge or invalidate selected pages.  For example, a user 
logs in and updates a page that's currently cached.  Can I 
remove/overwrite that particular page in an nginx caching proxy?

4) Any other words of wisdom regarding nginx vs varnish?

Thanks in Advance,

--- David