txLoadBalancer 1.1.0

Introduction

This is a pure python TCP load balancer. It takes inbound TCP connections and connects them to one of a number of backend servers.

txLoadBalancer is a fork of Anthony Baxter’s PythonDirector. It removed all threading and asyncore code and the admin UI with the Twisted-based analogs. It also significantly reorganized the API and provided many new features (see below).

Usage

$ twistd -noy ./bin/txlb.tac

This will use the default configuration file in ./etc/config.xml; you can edit the .tac file to point to the config you prefer. Be sure to edit the config.xml file to properly reflect your services in need of load-balancing.

To enable the admin interface, your config file must have the admin section defined, with the required fields. For an example, be sure to see ./etc/config.xml. For more details, please see the configuration information in the ./doc directory.

If you are creating your own script and don’t want to use txlb.tac, you can import the application setup functions in txlb.application.

If you want to “embed” a load-balancer in your Twisted application, see the example ./bin/txlbWeb.tac.

Features

• It is a pure-Twisted TCP loadbalancer.

• Thanks to Twisted, it’s async i/o based, so much less overhead than fork/thread based balancers.

• It has multiple scheduling algorithms (random, round robin, leastconns, weighted). If a server fails to answer, it’s removed from the pool - the client that failed to connect gets transparently failed over to a new host.

• Provides an optional builtin webserver for a built-in admin UI.

• Seperate management timer services that perform such tasks as periodically readding failed hosts to the rotation, updated on-disk config files with changes made to the running server.

• A built-in SSH server for managing (and modifying) a running load-balancer instance.

• A Twisted API for adding a load-balancing service to your Twisted application without the need to run a separate load-balancer.

• The application uses an XML-based configuration file.

Performance

(This section is currently incomplete)

Duncan’s notes from 2008, tested on a 2 CPU Sun Netra 240:

• a single apache instance on Solaris 10 * starting threads: * max threads

• 2 load-balanced apache instances on Solaris 10

• twisted.web instances on Solaris 10 (same docroot)

• 2 load-balanced twisted.web instances

• PythonDirector 1.0.0 proxies for 2 load-balanced twisted.web instances

Anthony’s original notes on performance:

• On my notebook, load balancing an apache on the same local ethernet (serving a static 18K text file) gets 155 connections per second and 2850 kbytes/s throughput (apachebench -n 2000 -c 10). Connecting directly to the apache gets 180 conns/sec and 3400kbytes/s. So unless you’re serving really really stupidly high hit rates it’s unlikely to be pythondirector causing you difficulties. (Note that 155 connections/sec is 13 million hits per day…)

• Running purely over the loopback interface to a local apache seems to max out at around 350 conns/second.

Changes