Sections¶

Arsenal’s configuration file is separated into sections. Each section begins with a bracket enclosed string. For example:

[director]

Begins the “director” configuration section. Each line following the section directive will populate that section’s configuration options, until another section directive is parsed, or the end of the file is reached.

Options¶

Each option has this basic format:

<option_name>=<value>

Where <option_name> is the option’s name, and <value> is the value to assign to the option.

A Short Example¶

The following:

[director]
dry_run=True

Would set the dry_run option to the boolean value ‘True’, which belongs to the [director] section.

Important Section Options¶

• scout - Configures which Scout will be loaded by arsenal-director to gather data from services. The Scout also currently handles issuing directives to endpoints. The format is:

  <scout_module_name>.<ScoutClassName>
  

  For example, setting the scout option to:

  devstack_scout.DevstackScout
  

  Would cause arsenal-director to use the DevStack Scout, which is a Scout provided by Arsenal that is designed to work with DevStack.

• dry_run - A boolean option. Setting this option to True will cause arsenal-director to run in dry run mode. Which means no directives generated by the configured Strategy will be issued.

• directive_spacing - An integer option. Represents time in seconds. Determines how long the Director will wait between issuing new directives returned by the configured Strategy.
• log_statistics - A boolean option. If True, Arsenal will log detailed statistics about nodes at the INFO level every time Arsenal issues directives. Statistics include: number of provisioned nodes, number of available nodes, number of cached nodes, a breakdown of which images have been cached and at what frequency. Also logs information broken up by flavor of node. If False, no statistics will be logged. Defaults to True.

module_class¶

The module_class option controls which Strategy object is loaded and subsequently used to provide Arsenal’s cache decisions. The format of the module_class option is as follows:

<strategy_module_name>.<StrategyClassName>

For example, the default value for module_class is:

simple_proportional_strategy.SimpleProportionalStrategy

This causes the the class SimpleProportionalStrategy, which can be found in the simple_proportional_strategy module, to be instantiated and used by arsenal-director to provide cache decisions at run-time. The simple_proportional_strategy module is included as part of Arsenal.

Astute readers will notice the the syntax of this option matches that of scout from the [director] section.

image_weights_filename¶

image_weights_filename is a string option specifying the location of a text file containing a single JSON object where the object’s keys are names of images as strings, and the values are the associated weights as non-negative integers. This JSON object is loaded as a Python dictionary and then referred to by Arsenal whenever a built-in image selection function, such as arsenal.strategy.choose_weighted_images_force_distribution, has to make a decision on which image(s) to choose to cache to available nodes.

Images with higher weights will tend to be picked more frequently, and similarly those with lower weights will tend to be picked less frequently.

Example JSON object containing image weights:

{
    'Ubuntu': 10,
    'CoreOS': 5,
    'Windows': 2,
    'SteamOS': 1
}

In the above example the Ubuntu image will be picked twice as often as the CoreOS image, and ten times as often as the SteamOS image. If you had 18 nodes to cache, then you can reasonably expect 10 nodes to have the Ubuntu image cached, 5 nodes to have the CoreOS image cached, and so on.

An example image weight json file is available in Arsenal’s source tree.

default_image_weight¶

default_image_weight is an integer value which is used to weight an image with no corresponding entry in the JSON object loaded by the image_weights_filename option. Defaults to 1.

Important Section Options¶

percentage_to_cache - A floating point number. Valid values range from 0 to 1 inclusive. 0 corresponds to 0%, and 1 corresponds to 100%. Controls the percentage of unprovisioned/available nodes of a particular flavor to be cached at a particular time.

Important Section Options¶

• call_max_retries - An integer value which determines how many times an individual client will be retried, until it is successful.
• call_retry_interval - An integer value which Determines how long the client wrapper will wait before trying a call again.

Cache Node¶

CacheNode instructs the endpoint to cache a specific image onto a specific node. This is the main mechanism used to build a fleet of cached nodes.

Eject Node¶

The second is EjectNode, which instructs the endpoint to do whatever is necessary to put a previously cached node back into an uncached state. This directive is necessary if an image cached to a node becomes out-of-date.