pen it will have and use features you list as not needed but the tool is so easy to use I am going to ignore you on those ;-)
Pen is a load balancer for udp and tcp based protocols such as dns, http or smtp. It
allows several servers to appear as one to the outside and automatically detects servers
that are down and distributes clients among the available servers. This gives high
availability and scalable performance.
The load balancing algorithm keeps track of clients and will try to send them back to the
server they visited the last time. The client table has a number of slots (default 2048,
settable through command-line arguments). When the table is full, the least recently used
one will be thrown out to make room for the new one.
pen 80 www1:8000:10 www2:80:10 www3
Here three servers cooperate in a web server farm. Host www1 runs its web server on port 8000 and accepts a maximum of 10 simultaneous connections. Host www2 runs on port 80 and accepts 10 connections. Finally, www3 runs its web server on port 80 and allows an unlimited number of simultaneous connections.
Oh and "In part inspired by balance by Thomas Obermair.".