I'm trying to scale a chatter app using socket.io + cluster. Is it possible for child processes to handle incoming request belong to its process id (assigned when fork)?
For example:
http://mydomain/calculate?process=1
The above request is only handled by process 1, other processes will ignore it. In this way, I want to make sure requests of the same room are handled by same process, so I may don't have to use RedisStore as socket.io backend.
I also wonder how RedisStore works, because when using it, I found io.sockets.manager.rooms data are not accurate in all processes.
Edit:
Put it another way: can cluster master process dispatch request to different child processes based on the querystring?
The answer is no. The OS takes care of load balancing in this situation and in order to process query string you already have to be connected to a web server ( in your case child process ).
From my experience I find cluster a bit useless. It is a lot easier to spawn multiple NodeJS processes ( on multiple ports ) and put a proxy ( nginx? ) in front of them. It is easy and scalable.
As for socket.io: I don't think it works correctly with cluster ( because of sharing global variables, which causes issues ). Again: spawning separate NodeJS processes should fix the problem. Also it will be useful once you reach the point when you will have to scale to multiple machines. Any tricks with cluster won't help you at that point.
One last note: socket.io does not scale well. I suggest writing your own WebSocket server ( based on WS for example ) and implement your own scaling mechanism. For example based on all-to-all UDP pinging, which should scale well when dealing with small amount of servers ( 50? 100? ).