LOAD BALANCER module

Admin Guide

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.

Also the module has the capability to do failover (to try a new destination if the selected one done not responde), to keep state of the destinations (to remember the failed destination and avoid using them agai) and to check the health of the destination (by doing probing of the destination and auto re-enabling).

How it works

Please refer to the Load-Balancer tutorial from the OpenSIPS website: /tutorials/loadbalancing/.

Probing and Disabling destinations

The module has the capability to monitor the status of the destinations by doing SIP probing (sending SIP requests like OPTIONS).

For each destination, you can configure what kind of probing should be done (probe_mode column):

(0) - no probing at all;
(1) - probing only when the destination is in disabled mode (disabling via MI command will competely stop the probing also). The destination will be automatically re-enabled when the probing will succeed next time;
(2) - probing all the time. If disabled, the destination will be automatically re-enabled when the probing will succeed next time;

A destination can become disabled in two ways:

script detection
MI command

Dependencies

OpenSIPS Modules

The following modules must be loaded before this module:

Dialog - Dialog module freeswitch. - only if “fetch_freeswitch_stats” is enabled.
dialog - TM module (only if probing is enabled)
clustere - only if “status_replication_cluster” option is enabled.
database - one of the DB modules

External Libraries or Applications

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

None.

Exported Parameters

db_url (string)

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

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

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

db_table (string)

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

Default value is “load_balancer”.

...
modparam("load_balancer", "db_table", "lb")
...

probing_interval (integer)

How often (in seconds) the probing of a destination should be done. If set to 0, the probing will be disabled as functionality (for all destinations)

Default value is “30”.

...
modparam("load_balancer", "probing_interval", 60)
...

probing_method (string)

The SIP method to be used for the probing requests.

Default value is ""OPTIONS"".

...
modparam("load_balancer", "probing_method", "INFO")
...

probing_from (string)

The FROM SIP URI to be advertised in the SIP probing requests.

Default value is ""sip:prober@localhost"".

...
modparam("load_balancer", "probing_from", "sip:pinger@192.168.2.10")
...

probing_reply_codes (string)

A comma separted list of SIP reply codes. The codes defined here will be considered as valid reply codes for probing messages, apart for 200.

Default value is “NULL”.

...
modparam("load_balancer", "probing_reply_codes", "501, 403")
...

probing_verbose (number)

A boolean option to enable extra logging related to the enabling or disabling of the destinations based on probing replies and MI commands.

A 0 value means disabled, anything else means enabled.

The extra logging will be done on INFO level.

Default value is “0” (disabled).

...
modparam("load_balancer", "probing_verbose", 1)
...

lb_define_blacklist (string)

Defines a blacklist based on a lb group. This list will contain the IPs (no port, all protocols) of the destinations matching the given group.

Multiple instances of this param are allowed.

Default value is “NULL”.

...
modparam("load_balancer", "lb_define_blacklist", "list= 1,4,3")
modparam("load_balancer", "lb_define_blacklist", "blist2= 2,10,6")
...

fetch_freeswitch_stats (integer)

If enabled, the maximum value of a resource may also consist of FreeSWITCH Event Socket Layer URLs, e.g. “channels=fs://:password@freeswitch.example.com” or “channels=fs://user:password@127.0.0.1:8021”. The default ESL port is 8021.

OpenSIPS will establish a connection with the given socket and periodically update the internal maximum value of the given resource using statistics pushed by the FreeSWITCH box.

The max value of a resource is updated every 20 seconds, as the stats arrive from FreeSWITCH.

Given the following format for FreeSWITCH heartbeat messages:

{
  ...
  "FreeSWITCH-Hostname": "pbx2",
  "FreeSWITCH-IPv4": "172.17.0.3",
  "Idle-CPU": "78.400000",
  "Max-Sessions": "1000",
  "Session-Count": "0",
  ...
}

, the load balancer uses the following formula in order to periodically update its “max_load” values for each FreeSWITCH box (FreeSWITCH data is highlighted in bold):

max_load = (Idle-CPU / 100) * (Max-Sessions - (Session-Count - current_load))

Default value is “0” (disabled).

...
modparam("load_balancer", "fetch_freeswitch_stats", 1)
...

initial_freeswitch_load (integer)

This parameter is only relevant for some seconds after module startup/reload, when no statistics from newly loaded FreeSWITCH ESL sockets have arrived, yet the routing of calls must remain unaffected. Any FreeSWITCH-enabled resource will inherit this value for the entire interval mentioned above (up to 20 seconds!).

Default value is “1000”.

...
modparam("load_balancer", "initial_freeswitch_load", 200)
...

status_replication_cluster (integer)

A cluster ID for sharing any change in the status of the destinations with other OpenSIPS instances that are part of a cluster. Whenever such a status changes (following an MI command, a probing result, a script command), the module will replicate this status change to all the nodes in the given cluster. A value of 0 means that sending replication data is disabled.

For more info on how to define and populate a cluster (with OpenSIPS nodes) see the “clusterer” module.

Default value is “0”.

...
# replicate LB status with all OpenSIPS in cluster ID 9
modparam("load_balancer", "status_replication_cluster", 9)
...

Exported Functions

lb_start(grp,resources[,flags])

The function starts a new load-balancing session over the available destinations. This translates into finding 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; this can be a number or a variable containing a numerical value.
resources - string containing a semi-colon separated list of resources required by the current call.
flags - various flags to controll the LB algorithm ( or computing the available load on the system):
- n - Negative availability - use destinations with negative availability (exceeded capacity); do not ignore resources with negative availability, and thus able to select for load balancing destinations with exceeded capacity. This might be needed in scenarios where we want to limit generic calls volume and always pass important/high-priority calls.
- r - Relative value - the relative available load (how many percentages are free) is used in computing the load of each pear/resource; Without this flag, the Absolute value is assumed - the effective available load ( maximum_load - current_load) is used in computing the load of each pear/resource.
- s - Pick a random destination if multiple destinations with the same load are found, instead of always picking first matched destination. This could help to offload an excessive load from the first destination and distribute load in situations when failed calls always routed to first destination, since they almost does not affect load counters of destinations.

The function may return:

1 (true) - if a new destination URI is set, pointing to the selected destination. NOTE that the RURI will not be changed by this function.
-1 (false) - generic internal error (memory allocation, parsing)
-2 (false) - no capacity available (detinations are up and available, but they do not have any availabe channels)
-3 (false) - no destinations available (the requested resources did not match any active destination)
-4 (false) - bad resources (requested resources do not exist)

This function can be used from REQUEST_ROUTE, BRANCH_ROUTE and FAILURE_ROUTE.

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

lb_next()

Function to be used to pull the next available (and less loaded) destination. You need to have an ongoing LB session (started with lb_start()).

This function is mainly used for implementing failover for the LB destinations.

The function may return:

1 (true) - if a new destination URI is set, pointing to the selected destination. NOTE that the RURI will not be changed by this function.
-1 (false) - generic internal error (memory allocation, parsing)
-2 (false) - no capacity available (detinations are up and available, but they do not have any availabe channels)
-3 (false) - no more destinations available (the requested resources did not match any active destination)

This function can be used from REQUEST_ROUTE and FAILURE_ROUTE.

...
if (t_check_status("(408)|(5[0-9][0-9])")) {
  /* check next available LB destination */
  if ( lb_next() ) {
    t_on_failure("1");
    xlog("-----------new dst is $du\n");
    t_relay();
    exit;
  }
}

...

lb_start_or_next(grp,resources[,flags])

This is just a wrapper function to simplify scripting. If there is no ongoing LB session, it acts as lb_start(); If there is an ongoing LB session, it acts as lb_next().

load_balance(grp,resources[,flags])

Old name of the lb_start_or_next() function.

Take care, this will become obsolete.

lb_reset()

Function to stop and flush a current LB session. To be used in failure route, if you want to stop the current LB session (not to try any other destinations from this session) and to start a completly new one.

This function can be used from REQUEST_ROUTE and FAILURE_ROUTE.

...
if (t_check_status("(5[0-9][0-9])")) {
  /* check next available LB destination */
  if ( lb_next() ) {
    t_on_failure("1");
    xlog("-----------new dst is $du\n");
    t_relay();
    exit;
  }
} else if (t_check_status("(408)")) {
  lb_reset();
  if (lb_start("1","conference")) {
    t_relay();
    exit;
  }
}
...

lb_is_started()

Function to check if there is any ongoing LB session. Returns true if so.

This function can be used in any type of route.

lb_disable_dst()

Marks as disabled the last destination that was used for the current call. The disabling done via this function will prevent the destination to be used for usage from now on. The probing mechanism can re-enable this peer (see the probing section in the beginning)

This function can be used from REQUEST_ROUTE and FAILURE_ROUTE.

...
if (t_check_status("(408)|(5[0-9][0-9])")) {
  lb_disable_dst();
  if ( lb_next() ) {
    t_on_failure("1");
    xlog("-----------new dst is $du\n");
    t_relay();
  } else {
    t_reply("500","Error");
  }
}

...

lb_is_destination(ip,port[,group[,active]])

Checks if the given IP and PORT belongs to a destination configured in the load-balancer’s list. Returns true if found and active (see the “active” parameter).

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE and LOCAL_ROUTE.

Meaning of the parameters is as follows:

ip and port - IP and PORT to be checked (any kind of variables are allowed, but take care as the PORT variables should have an integer value); A value 0 for the port means “any” - will match any port.
group - in what LB group the destination should be looked for; If not specified, the search will be in all groups.
active - if “1”, the search will be performed only over “active” (not disabled) destinations. If missing, the search will consider any kind of destinations.

...
if (lb_is_destination("$si","$sp") ) {
  # request from a LB destination
}
...

lb_count_call(ip,port,grp,resources[,undo])

The function counts the current call as load for a given destination with some given resources. Note that this call is not going through the load-balancing logic (there are not routing decision taken for the call); it is simply counted by LB as ongoing call for a destination;

Meaning of the parameters is as follows:

ip and port - IP and PORT to identify the destination the call has to be counted for.
grp - group id for the destinations; if no knows, “-1” will mean all groups.
resources - string containing a semi-colon separated list of resources required by the current call.
undo - (optional) if set to a non zero value, it will force the function to un-count - actually it will undo the counting of this call as load in the current LB session; this might be needed if we count call for particular resources and then need to un-count it.

Function returns true if the call was properly taken into consideration for estimating the load on the destination.

This function can be used from REQUEST_ROUTE, BRANCH_ROUTE and FAILURE_ROUTE.

...
# count as load also the calls orgininated by lb destinations
if (lb_is_destination("$si","$sp") ) {
  # inbound call from destination
  lb_count_call("$si","$sp","-1","conference");
} else {
  # outbound call to destinations
  if ( !load_balance("1","conference") ) {
    send_reply("503","unavailable");
    exit();
  }
  # dst URI points to the new destination
  xlog("sending call to $du\n");
  t_relay();
  exit;
}
...

Exported MI Functions

lb_reload

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

MI FIFO Command Format:

:lb_reload:_reply_fifo_file_
_empty_line_

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:

:lb_resize:_reply_fifo_file_
11   /*dstination id*/
voicemail  /*resource name*/
56   /* new resource capacity*/
_empty_line_

lb_list

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

MI FIFO Command Format:

    :lb_list:_reply_fifo_file_
    _empty_line_

$ ./opensipsctl fifo lb_list
Destination:: sip:127.0.0.1:5100 id=1 enabled=yes auto-re=on
        Resource:: pstn max=3 load=0
        Resource:: transc max=5 load=1
        Resource:: vm max=5 load=2
Destination:: sip:127.0.0.1:5200 id=2 enabled=no auto-re=on
        Resource:: pstn max=6 load=0
        Resource:: trans max=57 load=0
        Resource:: vm max=5 load=0

lb_status

Gets or sets the status (enabled or disabled) of a destination. The function takes 2 parameters, first mandatory, the id of the destiantion and second, optional, the new status. If no new status is given, the function will return the current status. If a new status is given (0 - disable, 1 - enable), this status will be forced for the destination.

MI FIFO Command Format:

    :lb_status:_reply_fifo_file_
    id
    status (optional)
    _empty_line_

$ ./opensipsctl fifo lb_status 2
enable:: no
$ ./opensipsctl fifo lb_status 2 1
$ ./opensipsctl fifo lb_status 2
enable:: yes

Exported Events

E_LOAD_BALANCER_STATUS

This event is raised when the module changes the state of a destination, either through MI or probing.

Parameters:

group - the group of the destination.
uri - the URI of the destination.
status - disabled if the destination was disabled or enabled if the destination is being used.

Developer Guide

Available Functions

NONE

Frequently Asked Questions

Q: Where can I find more about OpenSIPS?

Take a look at https://opensips.org/.

Q: 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 users@lists.opensips.org and e-mails regarding development versions should be sent to devel@lists.opensips.org.

If you want to keep the mail private, send it to users@lists.opensips.org.

Q: How can I report a bug?

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

doc copyrights:

Contributors

By Commit Statistics

Top contributors by DevScore⁽¹⁾, authored commits⁽²⁾ and lines added/removed⁽³⁾

#	Name	DevScore	Commits	Lines++	Lines—
1.	Bogdan-Andrei Iancu (@bogdan-iancu)	108	63	4072	602
2.	Liviu Chircu (@liviuchircu)	42	31	719	207
3.	Sergey Khripchenko (@shripchenko)	30	10	1105	563
4.	Razvan Crainea (@razvancrainea)	26	20	262	144
5.	Stefan Darius (@dariusstefan)	17	5	987	175
6.	Vlad Patrascu (@rvlad-patrascu)	12	8	103	138
7.	Vlad Paiu (@vladpaiu)	5	3	7	5
8.	Walter Doekes (@wdoekes)	5	3	4	4
9.	Jeremy Martinez (@JeremyMartinez51)	5	2	194	2
10.	Ezequiel Lovelle (@lovelle)	4	2	3	3

All remaining contributors: Anca Vamanu, Andrei Dragus, James Van Vleet, Dusan Klinec (@ph4r05), Zero King (@l2dy), TaoZhiying.

(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)

(2) including any documentation-related commits, excluding merge commits

(3) ignoring whitespace edits, renamed files and auto-generated files

By Commit Activity

#	Name	Commit Activity
1.	Razvan Crainea (@razvancrainea)	Oct 2010 - Jul 2026
2.	Bogdan-Andrei Iancu (@bogdan-iancu)	Feb 2009 - Jul 2026
3.	Stefan Darius (@dariusstefan)	Jun 2026 - Jul 2026
4.	Liviu Chircu (@liviuchircu)	Sep 2012 - Sep 2020
5.	Zero King (@l2dy)	Mar 2020 - Mar 2020
6.	TaoZhiying	May 2019 - May 2019
7.	Vlad Patrascu (@rvlad-patrascu)	Mar 2017 - Mar 2018
8.	Jeremy Martinez (@JeremyMartinez51)	Feb 2017 - Feb 2017
9.	Dusan Klinec (@ph4r05)	Dec 2015 - Dec 2015
10.	Sergey Khripchenko (@shripchenko)	Oct 2014 - Oct 2015

All remaining contributors: Ezequiel Lovelle (@lovelle), Walter Doekes (@wdoekes), Vlad Paiu (@vladpaiu), Andrei Dragus, James Van Vleet, Anca Vamanu.

(1) including any documentation-related commits, excluding merge commits

Documentation

Contributors

Last edited by: Razvan Crainea (@razvancrainea), Zero King (@l2dy), Bogdan-Andrei Iancu (@bogdan-iancu), Liviu Chircu (@liviuchircu), Vlad Patrascu (@rvlad-patrascu), Sergey Khripchenko (@shripchenko), Ezequiel Lovelle (@lovelle), Walter Doekes (@wdoekes), Vlad Paiu (@vladpaiu).

License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0