ratelimit Module

Ovidiu Sas

Bogdan Vasile Harjoc

Hendrik Scholz

Razvan Crainea

Edited by

Ovidiu Sas

Edited by

Bogdan Vasile Harjoc

Edited by

Hendrik Scholz

Edited by

Razvan Crainea

   Copyright © 2006 Freenet Cityline GmbH

   Copyright © 2008 VoIP Embedded Inc.

   Copyright © 2011 OpenSIPS Foundation
   Revision History
   Revision $Revision: 5901 $ $Date: 2009-07-21 10:45:05 +0300
                              (Tue, 21 Jul 2009) $
     __________________________________________________________

   Table of Contents

   1. Admin Guide

        1.1. Overview
        1.2. Use Cases
        1.3. Static Rate Limiting Algorithms

              1.3.1. Tail Drop Algorithm (TAILDROP)
              1.3.2. Random Early Detection Algorithm (RED)
              1.3.3. Network Algorithm (NETWORK)

        1.4. Dynamic Rate Limiting Algorithms

              1.4.1. Feedback Algorithm (FEEDBACK)

        1.5. Dependencies

              1.5.1. OpenSIPS Modules
              1.5.2. External Libraries or Applications

        1.6. Exported Parameters

              1.6.1. timer_interval (integer)
              1.6.2. expire_time (integer)
              1.6.3. hash_size (integer)
              1.6.4. default_algorithm (string)
              1.6.5. cachedb_url (string)
              1.6.6. db_prefix (string)

        1.7. Exported Functions

              1.7.1. rl_check(name, limit[, algorithm])
              1.7.2. rl_dec_count(name)
              1.7.3. rl_reset_count(name)

        1.8. Exported MI Functions

              1.8.1. rl_list
              1.8.2. rl_reset_pipe
              1.8.3. rl_set_pid
              1.8.4. rl_get_pid

   List of Examples

   1.1. Set timer_interval parameter
   1.2. Set expire_time parameter
   1.3. Set hash_size parameter
   1.4. Set default_algorithm parameter
   1.5. Set cachedb_url parameter
   1.6. Set db_prefix parameter
   1.7. rl_check usage
   1.8. rl_dec_count usage
   1.9. rl_reset_count usage

Chapter 1. Admin Guide

1.1. Overview

   This module implements rate limiting for SIP requests. In
   contrast to the PIKE module this limits the flow based on a per
   SIP request type basis and not per source IP. The latest
   sources allow you to dynamically group several messages into
   some entities and limit the traffic based on them. The MI
   interface can be used to change tunables while running
   OpenSIPS.

   This module is also integrated with the OpenSIPS Key-Value
   Interface, providing support for distributed rate limiting
   using Redis or Memcached CacheDB backends.

1.2. Use Cases

   Limiting the rate messages are processed on a system directly
   influences the load. The ratelimit module can be used to
   protect a single host or to protect an OpenSIPS cluster when
   run on the dispatching box in front.

   Distributed limiting is useful when the rate limit should be
   performed not only on a specific node, but on the entire
   platform. The internal limiting data will no longer be kept on
   each OpenSIPS instance. It will be stored in a distributed
   Key-Value database and queried by each instance before deciding
   if a SIP message should be blocked or not.

   NOTE: that this behavior only makes sense when the pipe
   algorithm used is TAILDROP or RED.

   A sample configuration snippet might look like this:
...
        if (!rl_check("$rU", "50", "TAILDROP")) {
                sl_send_reply("503", "Server Unavailable");
                exit;
        };
...

   Upon every incoming request listed above rl_check is invoked
   and the entity identified by the R-URI user is checked. It
   returns an OK code if the current per request load is below the
   configured threshold. If the load is exceeded the function
   returns an error and an administrator can discard requests with
   a stateless response.

1.3. Static Rate Limiting Algorithms

   The ratelimit module supports two different static algorithms
   to be used by rl_check to determine whether a message should be
   blocked or not.

1.3.1. Tail Drop Algorithm (TAILDROP)

   This is a trivial algorithm that imposes some risks when used
   in conjunction with long timer intervals. At the start of each
   interval an internal counter is reset and incremented for each
   incoming message. Once the counter hits the configured limit
   rl_check returns an error.

   The downside of this algorithm is that it can lead to SIP
   client synchronization. During a relatively long interval only
   the first requests (i.e. REGISTERs) would make it through.
   Following messages (i.e. RE-REGISTERs) will all hit the SIP
   proxy at the same time when a common Expire timer expired.
   Other requests will be retransmissed after given time, the same
   on all devices with the same firmware/by the same vendor.

1.3.2. Random Early Detection Algorithm (RED)

   Random Early Detection tries to circumvent the synchronization
   problem imposed by the tail drop algorithm by measuring the
   average load and adapting the drop rate dynamically. When
   running with the RED algorithm OpenSIPS will return errors to
   the OpenSIPS routing engine every n'th packet trying to evenly
   spread the measured load of the last timer interval onto the
   current interval. As a negative side effect OpenSIPS might drop
   messages although the limit might not be reached within the
   interval. Decrease the timer interval if you encounter this.

1.3.3. Network Algorithm (NETWORK)

   This algorithm relies on information provided by network
   interfaces. The total amount of bytes waiting to be consumed on
   all the network interfaces is retrieved once every
   timer_interval seconds. If the returned amount exceeds the
   limit specified in the modparam, rl_check returns an error.

1.4. Dynamic Rate Limiting Algorithms

   When running OpenSIPS on different machines, one has to adjust
   the drop rates for the static algorithms to maintain a sub 100%
   load average or packets start getting dropped in the network
   stack. While this is not in itself difficult, it isn't neither
   accurate nor trivial: another server taking a notable fraction
   of the cpu time will require re-tuning the parameters.

   While tuning the drop rates from the outside based on a certain
   factor is possible, having the algorithm run inside ratelimit
   permits tuning the rates based on internal server parameters
   and is somewhat more flexible (or it will be when support for
   external load factors - as opposed to cpu load - is added).

1.4.1. Feedback Algorithm (FEEDBACK)

   Using the PID Controller model (see Wikipedia page), the drop
   rate is adjusted dynamically based on the load factor so that
   the load factor always drifts towards the specified limit (or
   setpoint, in PID terms).

   As reading the cpu load average is relatively expensive
   (opening /proc/stat, parsing it, etc), this only happens once
   every timer_interval seconds and consequently the FEEDBACK
   value is only at these intervals recomputed. This in turn makes
   it difficult for the drop rate to adjust quickly. Worst case
   scenarios are request rates going up/down instantly by
   thousands - it takes up to 20 seconds for the controller to
   adapt to the new request rate.

   Generally though, as real life request rates drift by less,
   adapting should happen much faster.

1.5. Dependencies

1.5.1. OpenSIPS Modules

   The following modules must be loaded before this module:
     * No dependencies on other OpenSIPS modules.

1.5.2. External Libraries or Applications

   The following libraries or applications must be installed
   before running OpenSIPS with this module loaded:
     * None.

1.6. Exported Parameters

1.6.1. timer_interval (integer)

   The initial length of a timer interval in seconds. All amounts
   of messages have to be divided by this timer to get a messages
   per second value.

   IMPORTANT: A too small value may lead to performance penalties
   due to timer process overloading.

   Default value is 10.

   Example 1.1. Set timer_interval parameter
...
modparam("ratelimit", "timer_interval", 5)
...

1.6.2. expire_time (integer)

   This parameter specifies how long a pipe should be kept in
   memory until deleted.

   Default value is 3600.

   Example 1.2. Set expire_time parameter
...
modparam("ratelimit", "expire_time", 1800)
...

1.6.3. hash_size (integer)

   The size of the hash table internally used to keep the pipes. A
   larger table is much faster but consumes more memory. The hash
   size must be a power of 2 number.

   Default value is 1024.

   Example 1.3. Set hash_size parameter
...
modparam("ratelimit", "hash_size", 512)
...

1.6.4. default_algorithm (string)

   Specifies which algorithm should be assumed in case it isn't
   explicitly specified in the rl_check function.

   Default value is "TAILDROP".

   Example 1.4. Set default_algorithm parameter
...
modparam("ratelimit", "default_algorithm", "RED")
...

1.6.5. cachedb_url (string)

   Enables distributed rate limiting and specifies the backend
   that should be used by the CacheDB interface.

   Default value is "disabled".

   Example 1.5. Set cachedb_url parameter
...
modparam("ratelimit", "cachedb_url", "redis://root:root@127.0.0.1/")
...

1.6.6. db_prefix (string)

   Specifies what prefix should be added to the pipe name. This is
   only used when distributed rate limiting is enabled.

   Default value is "rl_pipe_".

   Example 1.6. Set db_prefix parameter
...
modparam("ratelimit", "db_prefix", "ratelimit_")
...

1.7. Exported Functions

1.7.1.  rl_check(name, limit[, algorithm])

   Check the current request against the pipe identified by name
   and changes/updates the limit. If no pipe is found, then a new
   one is created with the specified limit and algorithm, if
   specified. If the algorithm parameter doesn't exist, the
   default one is used.

   NOTE: A pipe's algorithm cannot be dynamically changed. Only
   the one specified when the pipe was created will be considered.

   The method will return an error code if the limit for the
   matched pipe is reached.

   Meaning of the parameters is as follows:
     * name - this is the name that identifies the pipe which
       should be checked. This parameter accepts both strings and
       pseudovariables.
     * limit - this specifies the threshold limit of the pipe. It
       is strongly related to the algorithm used. This parameter
       accepts an integer or a pseudovariable. Note that the limit
       should be specified as per-second, not per-timer_interval.
     * algorithm - this is parameter is optional and reffers to
       the algorithm used to check the pipe. If it is not set, the
       default value is used. It accepts a string or a
       pseudovariable.

   This function can be used from REQUEST_ROUTE.

   Example 1.7. rl_check usage
...
        # perform a pipe match for all INVITE methods using RED algorith
m
        if (is_method("INVITE")) {
                if (!rl_check("pipe_INVITE", "100", "RED")) {
                        sl_send_reply("503", "Server Unavailable");
                        exit;
                };
        };
...
        # use default algorithm for each different gateway
        $var(limit) = 10;
        if (!rl_check("gw_$ru", "$var(limit)")) {
                sl_send_reply("503", "Server Unavailable");
                exit;
        };
...

1.7.2.  rl_dec_count(name)

   This function decreases a counter that could have been
   previously increased by rl_check function.

   Meaning of the parameters is as follows:
     * name - identifies the name of the pipe.

   This function can be used from REQUEST_ROUTE.

   Example 1.8. rl_dec_count usage
...
        if (!rl_check("gw_$ru", "100", "TAILDROP")) {
                exit;
        } else {
                rl_dec_count("gw_$ru");
        };
...

1.7.3.  rl_reset_count(name)

   This function resets a counter that could have been previously
   increased by rl_check function.

   Meaning of the parameters is as follows:
     * name - identifies the name of the pipe.

   This function can be used from REQUEST_ROUTE.

   Example 1.9. rl_reset_count usage
...
        if (!rl_check("gw_$ru", "100", "TAILDROP")) {
                exit;
        } else {
                rl_reset_count("gw_$ru");
        };
...

1.8. Exported MI Functions

1.8.1.  rl_list

   Lists the parameters and variabiles in the ratelimit module.

   Name: rl_list

   Parameters:
     * pipe - indicates the name of the pipe. This parameter is
       optional. If it doesn't exist, all the active pipes are
       listed. Otherwise only the one specified.

   MI FIFO Command Format:
                :rl_list:_reply_fifo_file_
                gw_10.0.0.1
                _empty_line_

                :rl_list:_reply_fifo_file_
                _empty_line_

1.8.2.  rl_reset_pipe

   Resets the counter of a specified pipe.

   Name: rl_reset_pipe

   Parameters:
     * pipe - indicates the name of the pipe whose couter should
       be reset.

   MI FIFO Command Format:
                :rl_reset_pipe:_reply_fifo_file_
                gw_10.0.0.1
                _empty_line_

1.8.3.  rl_set_pid

   Sets the PID Controller parameters for the Feedback Algorithm.

   Name: rl_set_pid

   Parameters:
     * ki - the integral parameter.
     * kp - the proportional parameter.
     * kd - the derivative parameter.

   MI FIFO Command Format:
                :rl_set_pid:_reply_fifo_file_
                0.5
                0.5
                0.5
                _empty_line_

1.8.4.  rl_get_pid

   Gets the list of in use PID Controller parameters.

   Name: rl_get_pid

   Parameters: none

   MI FIFO Command Format:
                :rl_get_pid:_reply_fifo_file_
                _empty_line_
