RELB Easy Load Balancer

RELB Easy Load Balancer

RELB (RELB Easy Load Balancer) is a tiny, cross-platform TCP load balancer focused on performance, reliability, flexibility, and simplicity. It works with most TCP services and applications and can also act as a port redirector.

At its core, RELB listens for incoming TCP connections on specified IP addresses and ports, then forwards these connections to a pool of backend servers based on configurable rules and algorithms.

Features

  • Efficiently handles hundreds of simultaneous connections using minimal system resources.
  • Operates transparently for both clients and servers.
  • Plain-text configuration file that is simple and flexible.
  • Maintains persistence using an IP-based “Session Directory” so clients reconnect to the same server.
  • Intelligent server selection supporting weights, various assignment parameters, and round-robin behavior.
  • Rule-based filtering system to allow or deny server assignment based on client/server IP rules.
  • Integrated (optional) web administration interface for real-time monitoring and control.
  • Scheduled maintenance tasks (e.g., purging inactive connections, disconnecting clients).
  • Multi-platform: runs on Linux, Windows, and other major operating systems.

Getting Started

  1. Installation
  • See INSTALL for platform-specific build and install instructions.
  1. Configuration
  • Copy or create a configuration file (see relb.conf.sample for all options and examples).
  • Place it in the default location or point to it with the command-line option.
  1. Running RELB
  • Run relb from the command line. Optionally pass a configuration path.
  • Example: relb config /etc/relb.conf
  1. Management
  • Access the web admin interface at http://localhost:8182 (default) if enabled.
  • Warning: The admin interface is unencrypted and unauthenticated; restrict access appropriately.

Configuration

The configuration defines bind addresses, backend servers, filters, tasks, and other behavior. See relb.conf.sample and any additional documentation under doc/ for details.

Acknowledgments

RELB uses Hovik Melikyan’s C++ Portable Types Library (PTypes) originally from http://www.melikyan.com/. A patched version, updated for compatibility with modern C++ compilers, is available here: https://github.com/juan-rey/ptypes

Limitations

  • RELB only supports TCP connections; UDP is not supported.
  • IPv6 is not yet supported.
  • On Linux, the number of connections is limited by FD_SETSIZE (commonly 1024) and system resources.
  • On Windows, limits are mainly the available ephemeral ports (49152–65535) and system resources.

License

Licensed under the Open Software License version 3.0. See LICENSE.txt.

Support

Report issues, request features, or contribute via the project repository: https://github.com/juan-rey/relb

See doc/source_code_explained.md for details on code structure.