TricircleHowToReadCode

(Work in progress)Learn the source code of Tricircle step by step

Experience the multi-region Tricircle networking first

Follow the installation guide: https://github.com/openstack/tricircle/blob/master/doc/source/multi-pod-installation-devstack.rst

Learn the source code will be used in the "How to play":

Step 5: Create pod instances

Command issued:

 curl -X POST http://127.0.0.1:19999/v1.0/pods -H "Content-Type: application/json" \
     -H "X-Auth-Token: $token" -d '{"pod": {"region_name":  "CentralRegion"}}'

 curl -X POST http://127.0.0.1:19999/v1.0/pods -H "Content-Type: application/json" \
     -H "X-Auth-Token: $token" -d '{"pod": {"region_name":  "RegionOne", "az_name": "az1"}}'

• The restful API request will be routed to V1Controller from RootController for the version is 'v1.0':

 tricircle/tricircle/api/controllers/root.py
 ...
 class RootController(object):
      ...
     @expose()
     def _lookup(self, version, *remainder):
         if version == 'v1.0':
             return V1Controller(), remainder

• In V1Controller, because the request is to create pod, so the request will be forwarded to the post function in PodsController. Post function will create the pod and az mapping record in pod table:

 tricircle/tricircle/api/controllers/pod.py
 ...
 class PodsController(rest.RestController):
   ...
   @expose(generic=True, template='json')
   def post(self, **kw):
       context = t_context.extract_context_from_environ()
       ...
       new_pod = core.create_resource(
                   context, models.Pod,
                   {'pod_id': _uuid,
                    'region_name': region_name,
                    'pod_az_name': pod_az_name,
                    'dc_name': dc_name,
                    'az_name': az_name})

Step 6: Create network/subnet in central Neutron server

The central_plugin.py will be called because the core plugin of central Neutron is configured like this:

   core_plugin = tricircle.network.central_plugin.TricirclePlugin

Command issued:

 neutron --os-region-name=CentralRegion net-create net1
 neutron --os-region-name=CentralRegion subnet-create net1 10.0.1.0/24

• The request is handled by create_network when net1 is to be created:

 tricircle/tricircle/network/central_plugin.py
 ...
 class TricirclePlugin(db_base_plugin_v2.NeutronDbPluginV2,
                     security_groups.TricircleSecurityGroupMixin,
                     external_net_db.External_net_db_mixin,
                     portbindings_db.PortBindingMixin,
                     extradhcpopt_db.ExtraDhcpOptMixin,
                     l3_db.L3_NAT_dbonly_mixin,
                     l3_attrs_db.ExtraAttributesMixin):
  ...
  def create_network(self, context, network):
       net_data = network[attributes.NETWORK]
       ...

• The request is handled by create_subnet when 10.0.1.0/24 subnet is created in net1:

 tricircle/tricircle/network/central_plugin.py
 ...
 class TricirclePlugin(db_base_plugin_v2.NeutronDbPluginV2,
                     security_groups.TricircleSecurityGroupMixin,
                     external_net_db.External_net_db_mixin,
                     portbindings_db.PortBindingMixin,
                     extradhcpopt_db.ExtraDhcpOptMixin,
                     l3_db.L3_NAT_dbonly_mixin,
                     l3_attrs_db.ExtraAttributesMixin):
 ...
 def create_subnet(self, context, subnet):
       subnet_data = subnet['subnet']
       ...

Step 7: Get image ID and flavor ID which will be used in VM booting

Command issued:

 glance --os-region-name=RegionOne image-list
 nova --os-region-name=RegionOne flavor-list

No source code of Tricircle will be involved in this step.

Step 8: Boot virtual machines

Command issued:

 nova --os-region-name=RegionOne boot --flavor 1 --image $image1_id --nic net-id=$net1_id vm1
 nova --os-region-name=RegionTwo boot --flavor 1 --image $image2_id --nic net-id=$net2_id vm2

Please note, Nova in RegionOne is configured to use local Neutron in RegionOne, and RegionTwo's Nova will use local Neutron in RegionTwo. So different local Neutron will be called when booting instances in different Region.

In RegionOne local Neutron's configuration, the core plugin is configured like this:

 core_plugin = tricircle.network.local_plugin.TricirclePlugin

• When nova boot is executed in RegionOne Nova, Nova will send networks query with network id to local Neutron, and local plugin will send networks query request to central Neutron:

 tricircle/tricircle/network/local_plugin.py

 ...
 def get_networks(self, context, filters=None, fields=None,
                    sorts=None, limit=None, marker=None, page_reverse=False):
 ...
 t_networks = raw_client.list_networks(**params)['networks']

• raw_client.list_networks is to query networks in central Neutron, if the network existed in central Neutron, local plugin will create network/subnet with same uuid as that in central Neutron:

 tricircle/tricircle/network/local_plugin.py

 ...

 def get_networks(self, context, filters=None, fields=None,
                    sorts=None, limit=None, marker=None, page_reverse=False):
       ...
               b_network = self.core_plugin.create_network(
                   context, {'network': network})
               subnet_ids = self._ensure_subnet(context, network)