Projects / Pen


Pen is a load balancer for "simple" TCP-based protocols such as HTTP or SMTP. It allows several servers to appear as one to the outside. It automatically detects servers that are down and distributes clients among the available servers. This gives high availability and scalable performance.

Operating Systems

Recent releases

  •  16 Jun 2014 14:01

    Release Notes: This release adds IPv6 support for backend servers as well as the listening socket. Protocols can be mixed and matched among IPv4, IPv6, and Unix domain sockets. GeoIP support was also updated for IPv6.

    •  01 Apr 2014 07:47

      Release Notes: This release introduces support for Unix domain sockets in addition to Internet sockets. This new feature is available for the "main" listening socket as well as the control socket and allows access control using Unix file permissions. Documentation was updated to clarify what the control socket does.

      •  04 Feb 2014 12:12

        Release Notes: This release adds support for GeoIP access lists. It is now possible to restrict access to the load balancer using syntax such as "acl 0 permit country CA" and "acl 0 deny country SE". These access control entries can be mixed with the usual IP-based ones.

        •  21 Jan 2014 11:38

          Release Notes: The penctl and penlog utilities are now IPv6-compatible. The Automake configuration was updated. A clause was added to the license to explicitly permit distributing binaries linked with the openssl library.

          •  22 Nov 2013 14:02

            Release Notes: SSL support has been updated.

            Recent comments

            19 Dec 2006 01:45 moritz2282

            alternative XLB
            Hi, sorry for the blatant advertising, but I just finished the first release of XLB, which is only for HTTP but includes a connection management and caching.

            See (

            Thanks for feedback ;)


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