Django channels redis channel layer opens a lot of connections - django

Question

We ported a part of our application to django channels recently, using the redis channel layer backend. A part of our setup still runs on python2 in a docker which is why we use redis pub/sub to send messages back to the client. A global listener (inspired by this thread) catches all messages and distributes them into the django channels system. It all works fine so far but I see a lot of debug messages Creating tcp connection... passing by. The output posted below corresponds to one event. Both the listener as well as the consumer seem to be creating two redis connections. I have not enough knowledge about the underlying mechanism to be able to tell if this the expected behavior, thus me asking here. Is this to be expected?
The Listener uses a global channel layer instance:
# maps the publish type to a method name of the django channel consumer
PUBLISH_TYPE_EVENT_MAP = {
'state_change': 'update_client_state',
'message': 'notify_client',
}
channel_layer = layers.get_channel_layer()
class Command(BaseCommand):
help = u'Opens a connection to Redis and listens for messages, ' \
u'and then whenever it gets one, sends the message onto a channel ' \
u'in the Django channel system'
...
def broadcast_message(self, msg_body):
group_name = msg_body['subgrid_id'].replace(':', '_')
try:
event_name = PUBLISH_TYPE_EVENT_MAP[msg_body['publish_type']]
# backwards compatibility
except KeyError:
event_name = PUBLISH_TYPE_EVENT_MAP[msg_body['type']]
async_to_sync(channel_layer.group_send)(
group_name, {
"type": event_name,
"kwargs": msg_body.get('kwargs'),
})
The consumer is a JsonWebsocketConsumer that is initialized like this
class SimulationConsumer(JsonWebsocketConsumer):
def connect(self):
"""
Establishes the connection with the websocket.
"""
logger.debug('Incoming connection...')
# subgrid_id can be set dynamically, see property subgrid_id
self._subgrid_id = self.scope['url_route']['kwargs']['subgrid_id']
async_to_sync(self.channel_layer.group_add)(
self.group_name,
self.channel_name
)
self.accept()
And the method that is called from the listener:
def update_client_state(self, event):
"""
Public facing method that pushes the state of a simulation back
to the client(s). Has to be called through django channels
```async_to_sync(channel_layer.group_send)...``` method
"""
logger.debug('update_client_state event %s', event)
current_state = self.redis_controller.fetch_state()
data = {'sim_state': {
'sender_sessid': self.session_id,
'state_data': current_state}
}
self.send_json(content=data)
A single event gives me this output
listener_1 | DEBUG !! data {'publish_type': 'state_change', 'subgrid_id': 'subgrid:6d1624b07e1346d5907bbd72869c00e8'}
listener_1 | DEBUG !! event_name update_client_state
listener_1 | DEBUG !! kwargs None
listener_1 | DEBUG !! group_name subgrid_6d1624b07e1346d5907bbd72869c00e8
listener_1 | DEBUG Using selector: EpollSelector
listener_1 | DEBUG Parsing Redis URI 'redis://:#redis-threedi-server:6379/13'
listener_1 | DEBUG Creating tcp connection to ('redis-threedi-server', 6379)
listener_1 | DEBUG Parsing Redis URI 'redis://:#redis-threedi-server:6379/13'
listener_1 | DEBUG Creating tcp connection to ('redis-threedi-server', 6379)
threedi-server_1 | DEBUG Parsing Redis URI 'redis://:#redis-threedi-server:6379/13'
threedi-server_1 | DEBUG Creating tcp connection to ('redis-threedi-server', 6379)
threedi-server_1 | DEBUG update_client_state event {'type': 'update_client_state', 'kwargs': None}
threedi-server_1 | DEBUG Parsing Redis URI 'redis://:#redis-threedi-server:6379/13'
threedi-server_1 | DEBUG Creating tcp connection to ('redis-threedi-server', 6379)