Latest revision as of 14:37, 30 April 2014

Design

The intention of this document is to give a high level picture of the design of the OpenStack Python SDK. This document should cover how the SDK appears from the user perspective and important details of the internal design that the average user should not need to worry about.

User Interface Design

Internal Design

The internal design section of this document should cover aspects of the SDK that the typical user will not need to know. Developers and advanced users may find this information useful.

Authenticator

The Authenticator class is responsible for providing a valid authentication token and an appropriate endpoint for a service type. The authenticator can use a Transport to get a valid token if needed.

Connection

The internal design of the OpenStack Python SDK is based on the OSI Model where the application is the resource object. The objects are described in more detail below.

Resource

The Resource class represents a resource in the cloud, such as a compute instance, a stored object, a network, etc. Rather than have fixed attributes, its attributes should be populated with the information returned from the API. Every resource should have an id attribute; in the cases where there is not a native id, such as a stored object in Swift, an 'id' property should be created to return the unique identifier for the resource, such as a name. Well known attributes of a resource should be accessible through properties of the class.

Presentation

The job of the presentation layer is encoding and decoding of messages in the desired format. The default format is json and that is the only type currently supported, but it would be easy to add support for xml or text/plain. The Presentation class also manages the 'Accept' and 'Content-Type' headers to indicate the type of encoding. The presentation layer expects to communicate with a session layer.

Session

The session layer is responsible for maintaining an authorized session using the Authenticator. The authenticator is expected to provide a valid authentication token and an endpoint. The session layer manages the 'X-Auth-Token' header and sends requests over a transport layer. The session layer also makes sure the request is routed to the appropriate endpoint.

Transport

The Transport class is a wrapper for the requests.Session class and adds some common OpenStack functionality. The transport manages SSL certificate verification, the 'User-Agent' header and HTTP redirects. The transport also will allow logging of requests.

@@ Line 4: / Line 4: @@
 == User Interface Design ==
-===Internal Design ==
+== Internal Design ==
+The internal design section of this document should cover aspects of the SDK that the typical user will not need to know.  Developers and advanced users may find this information useful.
 === Authenticator ===
+The '''Authenticator''' class is responsible for providing a valid authentication token and an appropriate endpoint for a service type.  The authenticator can use a '''Transport''' to get a valid token if needed.
 === Connection ===
@@ Line 13: / Line 15: @@
 ==== Resource ====
-The '''Resource''' class represents a resource in the cloud, such as a compute instance, a stored object, a network, etc. Rather than have fixed attributes, its attributes should be populated with the information returned from the API. Every resource should have an '''id''' attribute; in the cases where there is not a native id, such as a stored object in Swift, an 'id' property should be created to return the unique identifier for the resource, such as a name.
+The '''Resource''' class represents a resource in the cloud, such as a compute instance, a stored object, a network, etc. Rather than have fixed attributes, its attributes should be populated with the information returned from the API. Every resource should have an '''id''' attribute; in the cases where there is not a native id, such as a stored object in Swift, an 'id' property should be created to return the unique identifier for the resource, such as a name.  Well known attributes of a resource should be accessible through properties of the class.
-==== Transport ====
+==== Presentation ====
-For each service there is a single '''Client''' class that contains the interface that the application developer will work with. Any functionality in the SDK should be available as a method in the Client class. Each Client instance has a reference to an instance of its Manager class. There is no logic in the Client class except to pass the request to its manager, and return the result from the manager to the application.
+The job of the presentation layer is encoding and decoding of messages in the desired format.  The default format is json and that is the only type currently supported, but it would be easy to add support for xml or text/plain.  The '''Presentation''' class also manages the 'Accept' and 'Content-Type' headers to indicate the type of encoding.  The presentation layer expects to communicate with a session layer.
-== General Design Principles ==
+==== Session ====
+The session layer is responsible for maintaining an authorized session using the '''Authenticator'''.  The authenticator is expected to provide a valid authentication token and an endpoint.  The session layer manages the 'X-Auth-Token' header and sends requests over a transport layer.  The session layer also makes sure the request is routed to the appropriate endpoint.
-* Whenever possible, equivalent parameters should be accepted. E.g., when acting on a resource, the user should be able to either supply the ID of that resource, or an instance on the Resource class corresponding to that resource.
+==== Transport ====
+The '''Transport''' class is a wrapper for the requests.Session class and adds some common OpenStack functionality.  The transport manages SSL certificate verification, the 'User-Agent' header and HTTP redirects.  The transport also will allow logging of requests.
-* While the Client class is the interface to the developer using this SDK in their applications, there is one exception for convenience: Resource objects may be interacted with directly where appropriate. In general any time you have a method that looks like:
-    <code>client.some_method(resource)</code>
-you should be able to work directly with the resource:
-    <code>resource.some_method()</code>
-For example, if you have a reference <code>server</code> to a compute resource, wish to delete a compute resource, you could call either <code>compute_client.delete(server)</code>, or <code>server.delete()</code>, and they would both result in the same action.

Difference between revisions of "PythonOpenStackSDK/ClassDesignDiscussion"