diff --git a/doc/source/devref/rpc_api.rst b/doc/source/devref/rpc_api.rst index 44be1cd44c6..15a800746e1 100644 --- a/doc/source/devref/rpc_api.rst +++ b/doc/source/devref/rpc_api.rst @@ -83,14 +83,76 @@ It is possible to bump the major version number and drop some code only needed for backwards compatibility. For more information about how to do that, see https://wiki.openstack.org/wiki/RpcMajorVersionUpdates. +Example Change +-------------- + +As an example minor API change, let's assume we want to add a new parameter to +my_remote_method_2. First, we add the argument on the server side. To be +backwards compatible, the new argument must have a default value set so that the +interface will still work even if the argument is not supplied. Also, the +interface's minor version number must be incremented. So, the new server side +code would look like this: + +:: + + from oslo import messaging + + + class ServerAPI(object): + + target = messaging.Target(version='1.2') + + def my_remote_method(self, context, arg1, arg2): + return 'foo' + + def my_remote_method_2(self, context, arg1, arg2=None): + if not arg2: + # Deal with the fact that arg2 was not specified if needed. + return 'bar' + +We can now update the client side to pass the new argument. The client must +also specify that version '1.2' is required for this method call to be +successful. The updated client side would look like this: + +:: + + from oslo import messaging + + from neutron.common import rpc as n_rpc + + + class ClientAPI(object): + """Client side RPC interface definition. + + API version history: + 1.0 - Initial version + 1.1 - Added my_remote_method_2 + 1.2 - Added arg2 to my_remote_method_2 + """ + + def __init__(self, topic): + target = messaging.Target(topic=topic, version='1.0') + self.client = n_rpc.get_client(target) + + def my_remote_method(self, context, arg1, arg2): + cctxt = self.client.prepare() + return cctxt.call(context, 'my_remote_method', arg1=arg1, arg2=arg2) + + def my_remote_method_2(self, context, arg1, arg2): + cctxt = self.client.prepare(version='1.2') + return cctxt.call(context, 'my_remote_method_2', + arg1=arg1, arg2=arg2) + Neutron RPC APIs ================ As discussed before, RPC APIs are defined in two parts: a client side and a -server side. Several of these pairs exist in the Neutron code base. +server side. Several of these pairs exist in the Neutron code base. The code +base is being updated with documentation on every rpc interface implementation +that indicates where the corresponding server or client code is located. -DHCP ----- +Example: DHCP +------------- The DHCP agent includes a client API, neutron.agent.dhcp_agent.DhcpPluginAPI. The DHCP agent uses this class to call remote methods back in the Neutron