How the SDK is organized

The following diagram shows how the project is laid out.

openstack/
    connection.py
    resource.py
    compute/
        compute_service.py
        v2/
            server.py
            _proxy.py
    tests/
        compute/
            v2/
                test_server.py

Resource

The openstack.resource.Resource base class is the building block of any service implementation. Resource objects correspond to the resources each service’s REST API works with, so the openstack.compute.v2.server.Server subclass maps to the compute service’s https://openstack:1234/v2/servers resource.

The base Resource contains methods to support the typical CRUD operations supported by REST APIs, and handles the construction of URLs and calling the appropriate HTTP verb on the given Adapter.

Values sent to or returned from the service are implemented as attributes on the Resource subclass with type openstack.resource.prop. The prop is created with the exact name of what the API expects, and can optionally include a type to be validated against on requests. You should choose an attribute name that follows PEP-8, regardless of what the server-side expects, as this prop becomes a mapping between the two.:

is_public = resource.prop('os-flavor-access:is_public', type=bool)

There are six additional attributes which the Resource class checks before making requests to the REST API. allow_create, allow_retreive, allow_commit, allow_delete, allow_head, and allow_list are set to True or False, and are checked before making the corresponding method call.

The base_path attribute should be set to the URL which corresponds to this resource. Many base_paths are simple, such as "/servers". For base_paths which are composed of non-static information, Python’s string replacement is used, e.g., base_path = "/servers/%(server_id)s/ips".

resource_key and resources_key are attributes to set when a Resource returns more than one item in a response, or otherwise requires a key to obtain the response value. For example, the Server class sets resource_key = "server" as an individual Server is stored in a dictionary keyed with the singular noun, and resource_keys = "servers" as multiple Servers are stored in a dictionary keyed with the plural noun in the response.

Proxy

Each service implements a Proxy class based on Proxy, within the openstack/<program_name>/vX/_proxy.py module. For example, the v2 compute service’s Proxy exists in openstack/compute/v2/_proxy.py.

The Proxy class is based on Adapter.

class openstack.proxy.Proxy(session, statsd_client=None, statsd_prefix=None, prometheus_counter=None, prometheus_histogram=None, *args, **kwargs)

Bases: keystoneauth1.adapter.Adapter

Represents a service.

retriable_status_codes = None

HTTP status codes that should be retried by default.

The number of retries is defined by the configuration in parameters called <service-type>_status_code_retries.

Each service’s Proxy provides a higher-level interface for users to work with via a Connection instance.

Rather than requiring users to maintain their own Adapter and work with lower-level Resource objects, the Proxy interface offers a place to make things easier for the caller.

Each Proxy class implements methods which act on the underlying Resource classes which represent the service. For example:

def list_flavors(self, **params):
    return flavor.Flavor.list(self.session, **params)

This method is operating on the openstack.compute.v2.flavor.Flavor.list method. For the time being, it simply passes on the Adapter maintained by the Proxy, and returns what the underlying Resource.list method does.

The implementations and method signatures of Proxy methods are currently under construction, as we figure out the best way to implement them in a way which will apply nicely across all of the services.

Connection

The openstack.connection.Connection class builds atop a openstack.config.cloud_region.CloudRegion object, and provides a higher level interface constructed of Proxy objects from each of the services.

The Connection class’ primary purpose is to act as a high-level interface to this SDK, managing the lower level connecton bits and exposing the Resource objects through their corresponding Proxy object.

If you’ve built proper Resource objects and implemented methods on the corresponding Proxy object, the high-level interface to your service should now be exposed.