CloudKitty’s Architecture¶

Module loading and extensions¶

Nearly every part of CloudKitty makes use of stevedore to load extensions dynamically.

Every rating module is loaded at runtime and can be enabled/disabled directly via CloudKitty’s API. The module is responsible of its own API to ease the management of its configuration.

Collectors and storage backends are loaded with stevedore but configured in CloudKitty’s configuration file.

Collector¶

Loaded with stevedore

The name of the collector to use is specified in the configuration. For now, only one collector can be loaded at once. This part is responsible for information gathering. It consists of a python class that loads data from a backend and returns it in a format that CloudKitty can handle.

The data format of CloudKitty is the following:

{
    "myservice": [
        {
            "rating": {
                "price": 0.1
            },
            "desc": {
                "sugar": "25",
                "fiber": "10",
                "name": "apples",
            },
            "vol": {
                "qty": 1,
                "unit": "banana"
            }
        }
    ]
}

For information about how to write a custom collector, see the developer documentation.

Rating¶

Loaded with stevedore

This is where every rating calculations is done. The data gathered by the collector is pushed in a pipeline of rating processors. Every processor does its calculations and updates the data.

Example of minimal rating module (taken from the Noop module):

class Noop(rating.RatingProcessorBase):

    controller = NoopController
    description = 'Dummy test module'

    @property
    def enabled(self):
        """Check if the module is enabled

        :returns: bool if module is enabled
        """
        return True

    @property
    def priority(self):
        return 1

    def reload_config(self):
        pass

    def process(self, data):
        for cur_data in data:
            cur_usage = cur_data['usage']
            for service in cur_usage:
                for entry in cur_usage[service]:
                    if 'rating' not in entry:
                        entry['rating'] = {'price': decimal.Decimal(0)}
        return data

Storage¶

Loaded with stevedore

The storage module is responsible for storing and retrieving data in a backend. It implements two interfaces (v1 and v2), each providing one or more drivers. For more information about the storage backend, see the configuration section.

Writer¶

Loaded with stevedore

In the same way as the rating pipeline, the writing is handled with a pipeline. The data is pushed to write orchestrator that will store the data in a transient DB (in case of output file invalidation). And then to every writer in the pipeline which is responsible of the writing.