How To Handle Socket Connections In A Docker-swarm Environment
I am building a webapplication using nodejs as the server and Docker Swarm to handle replication and load balancing.
Right now, I need to handle real-time data updates between clients and the replicated servers, so i thought of using Socket.IO to handle the connections. All the requests pass via an NGINX server that redirect it to the manager node of the swarm, and its him that handles the balancing. Since the topology of the network can change rapidly based on the load of the network, i am reticent of letting NGINX handle the balancing and applying sticky sessions... (maybe am wrong)
For my understanding with this setup, if a client connects to my server, the load balancer of docker will send the request to one of my N replicated servers, and this an only this server will know that the client connected. So, its possible that if some traditional HTTP-Request updates my data on another replica, the information will not be sent because of the lack of existence of this connection in the given server.
Is there a way of handling situations like this? I thought of including a Message queue between servers to send the data to all of them and then the one containing the connection will send the data, but is that the recommended way of doing it?
Thank you very much
I investigated a bit further since the time of the question. I'll post what I found in case it helps somebody with a similar issue.
One option i found is to use a MessageQueue or something similar to broadcast the messages to all the replicas, then each one filters only the messages that can send because the replica itself has knowledge of the TCP connections available in that replica.
But i think that would put excessive stress over the replicas because all of them are receiving all of the messages, so one solution would be to create a queue or a service that links the id of the given connection to the replica, and forward the messages only to those replicas interested. I think it can be easily done with topics or making a queue for each tcp connection with some id as a identifier, and then pushing to the corresponding queue.
If anyone sees any problem or wants to add something, it will be very much appreciated!
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