I am moving many sites from an old web server to a new one. It needs to be done as transparently as possible.
The sites are backed by a WCMS, so there is a possibility that clients can make changes to what is actually their old site. To avoid this, I was thinking of setting up either a TCP or HTTP proxy on the old machine which transparently forwards on to the new machine. This would greatly reduce pressure to deal with the DNS, which is going to be a colossal job in itself due to some poorly made decisions in the past.
Should I use an HTTP or TCP proxy, or is this just generally a bad call? Note that I am dealing with a few thousand sites basically on my own.