The oslo.messaging library takes the existing RPC code from oslo and
wraps it in a sane API with well defined semantics around which we can
make a commitment to retain compatibility in future.
The patch is large, but the changes can be summarized as:
* oslo.messaging>=1.3.0a4 is required; a proper 1.3.0 release will be
pushed before the icehouse release candidates.
* The new rpc module has init() and cleanup() methods which manage the
global oslo.messaging transport state. The TRANSPORT and NOTIFIER
globals are conceptually similar to the current RPCIMPL global,
except we're free to create and use alternate Transport objects
in e.g. the cells code.
* The rpc.get_{client,server,notifier}() methods are just helpers
which wrap the global messaging state, specifiy serializers and
specify the use of the eventlet executor.
* In oslo.messaging, a request context is expected to be a dict so
we add a RequestContextSerializer which can serialize to and from
dicts using RequestContext.{to,from}_dict()
* The allowed_rpc_exception_modules configuration option is replaced
by an allowed_remote_exmods get_transport() parameter. This is not
something that users ever need to configure, but it is something
each project using oslo.messaging needs to be able to customize.
* We maintain a global NOTIFIER object and create specializations of
it with specific publisher IDs in order to avoid notification driver
loading overhead.
* rpc.py contains transport aliases for backwards compatibility
purposes. setup.cfg also contains notification driver aliases for
backwards compat.
* The messaging options are moved about in cinder.conf.sample because
the options are advertised via a oslo.config.opts entry point and
picked up by the generator.
* We use messaging.ConfFixture in tests to override oslo.messaging
config options, rather than making assumptions about the options
registered by the library.
Implements blueprint: oslo-messaging
Change-Id: Ib912809428d92e788558439e2d85b51272ebefdd
bcd9f363ff