1.1. Overview

The cfgutils module can be used to introduce some randomness to the behaviour of the server. It provides some setup functions and the "rand_event" function. This function return either true or false, depending on a random value and a specified probability. E.g. if you set via fifo or script a probability value of 5%, then 5% of all calls to rand_event will return true. The pseudovariable "$RANDOM" could be used to introduce random values e.g. into a SIP reply.

The benefit of this module is the probability of the decision can be manipulated by external applications such as web interface or command line tools. The probability must be specified as percent value, ranging from 0 to 100.

The module exports commands to FIFO server that can be used to change the global settings via FIFO interface. The FIFO commands are: "set_prob", "reset_prob" and "get_prob".

This module can be used for simple load-shedding, e.g. reply 5% of the Invites with a 503 error and a adequate random Retry-After value.

Due the openser architecture the module uses only one seed for all the children, that means if you have for example three children, the random descision and the returned random value will repeat three times.

The module provides as well some functions to delay the execution of the server. The functions "sleep" and "usleep" could be used to let the server wait a specific time interval.

1.2. Dependencies

The module depends on the following modules (in the other words the listed modules must be loaded before this module):

• none

1.3. Exported Parameters

   
modparam("cfgutils", "initial_probability", 15)
   

1.4. Exported Functions

...
if (rand_event()) {
  append_to_reply("Retry-After: 120\n");
  sl_send_reply("503", "Try later");
  exit;
};
# normal message processing follows
...

...
rand_set_prob("4");
...

...
rand_reset_prob();
...

...
rand_get_prob();
   

...
sleep("1");
...
			

...
usleep("500");
...
			

1.5. MI Commands

...
$ openserctl fifo rand_set_prob 10
200 OK
...

...
$ openserctl fifo rand_reset_prob
200 OK
...

...
$ openserctl fifo get_prob
200 OK
The actual probability is 50 percent.
...

1.6. Exported pseudo-variables

...
if (get_random()) {
  $avp(i:10) = ($RANDOM / 16777216); # 2^24
  if ($avp(i:10) < 10) {
     $avp(i:10) = 10;
  }
  append_to_reply("Retry-After: $avp(i:10)\n");
  sl_send_reply("503", "Try later");
  exit;
};
# normal message processing follows