Perlbal is a single-threaded event-based server supporting HTTP load
balancing, web serving, and a mix of the two.

One of the defining things about Perlbal is that almost everything can
be configured or reconfigured on the fly without needing to restart the
software. A basic configuration file containing a management port enables
you to easily perform operations on a running instance of Perlbal.

See also: https://www.danga.com/perlbal/