Merge "Drop usage of rpc compat layer"
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=============================
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Dropping rpc API compat layer
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=============================
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https://blueprints.launchpad.net/neutron/+spec/drop-rpc-compat
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This proposal is to make more direct use of oslo.messaging APIs throughout
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Neutron instead of a compatibility layer based on an old API.
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Problem Description
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===================
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Neutron has migrated from the rpc code in oslo-incubator to the oslo.messaging
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library. The oslo.messaging library has a different (but better) API. To ease
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the transition to oslo.messaging, Neutron has used some compatibility code to
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convert the older style API usage to oslo.messaging APIs. This proposal is to
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make more direct use of oslo.messaging APIs throughout Neutron.
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Moving toward more direct usage of oslo.messaging APIs will improve consistency
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with other projects, since all projects should be converging on the newer style
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APIs.
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Proposed Change
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===============
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The following classes are items considered as a part of the compatibility layer.
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The direct use of each of these things will be removed and replaced with direct
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use of equivalent and underlying oslo.messaging APIs.
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neutron.common.rpc.
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RpcProxy
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RpcCallback
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RPCException
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RemoteError
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MessagingTimeout
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This looks like a small list, but it's more invasive than it looks. It will be
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broken up into several iterative patches that are more easily reviewed and
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merged over time.
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Here are some examples of the most invasive conversions (RpcProxy and
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RpcCallback)::
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from oslo import messaging
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from neutron.common import rpc as n_rpc
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Old style client interface using RpcProxy::
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class ClientAPI(n_rpc.RpcProxy):
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BASE_RPC_API_VERSION = '1.0'
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def __init__(self, topic):
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super(DhcpPluginApi, self).__init__(
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topic=topic, default_version=self.BASE_RPC_API_VERSION)
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def remote_method(self, context, arg1):
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return self.call(context,
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self.make_msg('remote_method',
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arg1=arg1))
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def remote_method_2(self, context, arg1, arg2):
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return self.call(context,
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self.make_msg('remote_method_2',
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arg1=arg1, arg2=arg2),
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version='1.1')
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New style client interface::
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class ClientAPI(object):
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def __init__(self, topic):
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target = messaging.Target(topic=topic, version='1.0')
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self.client = n_rpc.get_client(target)
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def remote_method(self, context, arg1):
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cctxt = self.client.prepare()
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return cctxt.call(context, 'remote_method', arg1=arg1)
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def remote_method_2(self, context, arg1, arg2):
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cctxt = self.client.prepare(version='1.1')
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return cctxt.call(context, 'remote_method_2', arg1=arg1, arg2=arg2)
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Old style server interface::
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class ServerAPI(n_rpc.RpcCallback):
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RPC_API_VERSION = '1.1'
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def remote_method(self, context, arg1):
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return 'foo'
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def remote_method_2(self, context, arg1, arg2):
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return 'bar'
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New style server interface::
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class ServerAPI(object):
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target = messaging.Target(version='1.1')
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def remote_method(self, context, arg1):
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return 'foo'
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def remote_method_2(self, context, arg1, arg2):
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return 'bar'
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Data Model Impact
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-----------------
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None
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REST API Impact
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---------------
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None
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Security Impact
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---------------
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None
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Notifications Impact
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--------------------
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None
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Other End User Impact
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---------------------
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None
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Performance Impact
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------------------
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Negligible. In theory, this is removing a compatibility layer so there should
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be less code, but the overall performance impact of removing the layer is
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negligible in the broader scope of things.
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Other Deployer Impact
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---------------------
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None
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Developer Impact
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----------------
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There are several impacts to developers. Developers used to the older rpc API
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(and the equivalent compatibility layers) will have to learn what's different.
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Arguably, it's conceptually quite similar so this shouldn't have a large impact.
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The oslo.messaging library itself has documentation. Looking at all of the
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existing code once it has been converted will help quite a bit as well, since
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you can just follow the existing pattern.
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The other impact is patch conflicts. Since this work involves some minor
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refactoring across the tree, it may conflict with other code in progress. This
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will only occur in the case of features that modify rpc APIs. The changes will
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be done in a series of smaller changes, which will help with rebasing and fixing
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conflicts against smaller sets of updates at a time.
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Community Impact
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----------------
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None.
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Alternatives
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------------
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The alternative is to leave the compatibility layer in place. The downsides of
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this are that Neutron's use of oslo.messaging will diverge further and further
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from what the rest of OpenStack messaging usage looks like. It may also make it
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more difficult to take advantage of new features in oslo.messaging in the
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future.
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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russellb
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Work Items
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----------
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The usage of each class listed in the proposed change section will be removed
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one at a time. The removal of each will be broken up into several changes, one
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per interface (rpc API).
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Dependencies
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============
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* None
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Testing
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=======
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The unit tests will be updated as required. New ones will be added in key
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places where unit test coverage may be missing.
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There are no functional changes here, so all of the existing unit and functional
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tests will be relied upon to help ensure that no regressions are introduced.
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Tempest Tests
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-------------
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None.
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Functional Tests
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----------------
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None.
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API Tests
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---------
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None.
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Documentation Impact
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====================
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None.
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User Documentation
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------------------
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None.
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Developer Documentation
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-----------------------
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None.
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References
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==========
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* Existing oslo.messaging documentation:
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http://docs.openstack.org/developer/oslo.messaging/
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