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_update, 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, within the
openstack/<program_name>/vX/_proxy.py module. For example, the v2 compute
service’s Proxy exists in openstack/compute/v2/_proxy.py.
This Proxy class contains a Adapter and
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
os_client_config.config.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.