There was an interesting question in the Nginx mailing list regarding replacing Varnish with Nginx as a load balancer. Let me quote the question directly here…
We are using Varnish in front of 3 load balanced web servers running apache. We had migrated from one hosting platform where we had 1 app server and 1 database server using Varnish (Drupal 6.x) and had no issues. Now that we are running in a load balanced environment (3 load balanced apache web servers, a Varnish server, and 1 database server) we are seeing mulitple examples of cacheing issues. (Pages not displaying correctly… style issues, data input staying cached and used on another page, etc).
We think we can just replace the Varnish server and use a NGinx server. I don’t want to necessarily remove all the apache servers, but we have to get this cacheing issue corrected….