Avoid running periodic tasks on all workers

This patch registers periodic tasks only to the main process,
ensuring that they run once per instance (or group of workers).

Closes-Bug: #1717548
Change-Id: Ie0038207ccdfa04d0c14c7194835c9d4c470fecc

zun/cmd/compute.py

@@ -42,4 +42,5 @@ def main():
     server = rpc_service.Service.create(CONF.compute.topic, CONF.host,
                                         endpoints, binary='zun-compute')
     launcher = service.launch(CONF, server)
+    server.create_periodic_tasks()
     launcher.wait()

zun/common/rpc_service.py

@@ -60,6 +60,9 @@ class Service(service.Service):
         profiler.setup(binary, CONF.host)
 
     def start(self):
+        self._server.start()
+
+    def create_periodic_tasks(self):
         servicegroup.setup(CONF, self.binary, self.tg)
         periodic.setup(CONF, self.tg)
         for endpoint in self.endpoints:
@@ -68,7 +71,6 @@ class Service(service.Service):
                 periodic_interval_max=CONF.periodic_interval_max,
                 context=context.get_admin_context(all_tenants=True)
             )
-        self._server.start()
 
     def stop(self):
         if self._server: