Rackspace-specific Rate Limit Preprocessor for Turnstile

This package provides the rs_limits Python module, which contains the rs_preprocess() preprocessor for use with Turnstile. This module works together with nova_limits to provide class-based rate limiting integration with nova in the Rackspace. To use, you must configure the Turnstile middleware with the following configuration:

[filter:turnstile]
use = egg:turnstile#turnstile
enable = rs_limits nova_limits
formatter = nova_limits
redis.host = <your Redis database host>

Then, simply use the nova_limits rate limit class in your limits configuration.

The rs_limits.rs_preprocess() preprocessor derives the rate-limit class from the "X-PP-Groups" header of the request, if present. It expects the database to contain a key "rs-group:<group name>" mapping the group name to a rate-limit class; if no such key exists, the next group name will be tried.

Note that rs_limits must be listed in the enable key of the configuration immediately before nova_limits.

Mapping Groups to Rate Limit Classes

A group_class command is provided to control the mapping of the group to the rate limit class. A usage summary follows:

usage: group_class [-h] [--debug] [--delete] [--class KLASS] config group

Set up or query limit classes associated with groups.

positional arguments:
  config                Name of the configuration file, for connecting to the
                        Redis database.
  group                 Name of the group.

optional arguments:
  -h, --help            show this help message and exit
  --debug, -d           Run the tool in debug mode.
  --delete, -D          Delete the group from the database.
  --class KLASS, -c KLASS
                        If specified, sets the class associated with the given
                        group.

Repose Group Priority Bug

Repose places groups in the "X-PP-Groups" header, giving them all a quality factor. Unfortunately, at least some versions of Repose hard-code this quality factor, making it difficult to determine which group should be given priority in the rate limit class selection algorithm. To work around this, the rs_limits.rs_preprocess() function allows group priorities to be set using a Turnstile configuration option. These priorities are only used if all groups in the "X-PP-Groups" header have a quality factor of 1.0.

The configuration option to use is rs_limits.groups. The value for this option is a comma-separated list of "key=value" pairs, where the "key" is the name of a group, and the "value" is a float in the interval [0.0, 1.0]. If a group is specified in "X-PP-Groups" which does not exist in this list of groups, it will be given a default priority of 0.1. This default value can be altered by specifying an entry without a key; e.g., to specify a default priority of 0.05, use "=0.05" in the groups list.

Note that, when using this built-in group priority system, group names are considered in a case insensitive manner. The case used in the "X-PP-Groups" header will, however, be preserved.