Load-Balancer Module

Bogdan-Andrei Iancu

Voice Sistem SRL

Edited by

Bogdan-Andrei Iancu

Revision History
Revision $Revision: 5886 $$Date: 2009-07-16 12:54:34 +0200 (Thu, 16 Jul 2009) $

Table of Contents

1. Admin Guide
1.1. Overview
1.2. How it works
1.3. Dependencies
1.3.1. OpenSIPS Modules
1.3.2. External Libraries or Applications
1.4. Exported Parameters
1.4.1. db_url (string)
1.4.2. db_table (string)
1.5. Exported Functions
1.5.1. load_balance(grp,resources)
1.6. Exported statistics
1.7. Exported MI Functions
1.7.1. lb_reload
1.7.2. lb_resize
1.7.3. lb_list
1.8. Exported pseudo-variables
2. Developer Guide
2.1. Available Functions
3. Frequently Asked Questions

List of Examples

1.1. Set db_url parameter
1.2. Set db_table parameter
1.3. load_balance usage

Chapter 1. Admin Guide

1.1. Overview

The Load-Balancer module comes to provide traffic routing based on load. Shortly, when OpenSIPS routes calls to a set of destinations, it is able to keep the load status (as number of ongoing calls) of each destination and to choose to route to the less loaded destination (at that moment). OpenSIPS is aware of the capacity of each destination - it is preconfigured with the maximum load accepted by the destinations. To be more precise, when routing, OpenSIPS will consider the less loaded destination not the destination with the smallest number of ongoing calls, but the destination with the largest available slot.

1.2. How it works

Please refer to the Load-Balancer tutorial from the OpenSIPS website: http://www.opensips.org/index.php?n=Resources.DocsTutLoadbalancing.

1.3. Dependencies

1.3.1. OpenSIPS Modules

The following modules must be loaded before this module:

  • Dialog - Dialog module

  • database - one of the DB modules

1.3.2. External Libraries or Applications

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

  • None.

1.4. Exported Parameters

1.4.1. db_url (string)

The URL pointing to the database where the load-balancing rules are stored.

Default value is “mysql://opensips:opensipsrw@localhost/opensips”.

Example 1.1. Set db_url parameter

modparam("load_balancer", "db_url", "dbdriver://username:password@dbhost/dbname")

1.4.2. db_table (string)

The name of the DB table containing the load-balancing rules.

Default value is “load_balancer”.

Example 1.2. Set db_table parameter

modparam("", "db_table", "lb")

1.5. Exported Functions

1.5.1.  load_balance(grp,resources)

The function performs load-balancing over the available destinations in order to find the less loaded destination that can provide the requested resources and belong to a requested group.

Meaning of the parameters is as follows:

  • grp - group id for the destinations; the destination may be grouped in several groups you can you for differnet scenarios.

  • resources - string containing a semi-colon list of resources required by the current call.

Function returns true is a new destination URI is set pointing to the selected destiantion. NOTE that the RURI will not be changed by this function.


Example 1.3. load_balance usage

if (load_balance("1","trascoding;conference")) {
	# dst URI points to the new destination
	xlog("sending call to $du\n");

1.6. Exported statistics


1.7. Exported MI Functions

1.7.1. lb_reload

Trigers the reload of the load balancing data from the DB.

MI FIFO Command Format:


1.7.2. lb_resize

Changes the capacity for a resource of a destination. The function receives as parameters the ID (as per DB) of the destination along with the name of the resource you want to resize.

MI FIFO Command Format:

		11   /*dstination id*/
		voicemail  /*resource name*/
		56   /* new resource capacity*/

1.7.3. lb_list

Lists all the destinations and the maximum and current load for each resource of the destination.

MI FIFO Command Format:


1.8. Exported pseudo-variables


Chapter 2. Developer Guide

2.1. Available Functions


Chapter 3. Frequently Asked Questions


Where can I find more about OpenSIPS?

Take a look at http://www.opensips.org/.


Where can I post a question about this module?

First at all check if your question was already answered on one of our mailing lists:

E-mails regarding any stable OpenSIPS release should be sent to and e-mails regarding development versions should be sent to .

If you want to keep the mail private, send it to .


How can I report a bug?

Please follow the guidelines provided at: https://github.com/OpenSIPS/opensips/issues.