cloudkitty/doc/source/developer/fetcher.rst

Scope fetcher

The fetcher retrieves a list of scopes to rate. These scopes are then passed to the collector, in combination with each metric type.

Implementation

Fetchers are extremely simple. A custom fetcher must implement the following class:

cloudkitty.fetcher.BaseFetcher

The get_tenants method takes no parameters and returns a list of unique scope_ids, represented as str.

The name of the new fetcher must be specified as a class attribute.

Options for the new fetcher must be registered under the fetcher_<name> config section.

A new scope fetcher must be implemented in a new module, in cloudkitty.fetcher.<name>.py. Its class must be called <Name>Fetcher.

An entrypoint must be registered for new fetchers. This is done in the setup.cfg file, located at the root of the repository:

cloudkitty.fetchers =
    keystone = cloudkitty.fetcher.keystone:KeystoneFetcher
    source = cloudkitty.fetcher.source:SourceFetcher
    # [...]
    custom = cloudkitty.fetcher.custom:CustomFetcher

Example

The most simple scope fetcher is the SourceFetcher. It simply returns a list of scopes read from the configuration file:

# In cloudkitty/fetcher/source.py
from oslo_config import cfg

from cloudkitty import fetcher

FETCHER_SOURCE_OPTS = 'fetcher_source'

fetcher_source_opts = [
    cfg.ListOpt(
        'sources',
        default=list(),
        help='list of source identifiers',
    ),
]

# Registering the 'sources' option in the 'fetcher_source' option
cfg.CONF.register_opts(fetcher_source_opts, FETCHER_SOURCE_OPTS)

CONF = cfg.CONF


class SourceFetcher(fetcher.BaseFetcher):

    # Defining the name of the fetcher
    name = 'source'

    # Returning the list of scopes read from the configuration file
    def get_tenants(self):
        return CONF.fetcher_source.sources

More complex examples can be found in the cloudkitty/fetcher directory.