Hi all
I'm building a simple TCP load balancer based on a code snippet from Glyph
on SO:
http://stackoverflow.com/questions/4096061/general-question-regarding-wether-or-not-use-twisted-in-tcp-proxy-project
It's served me well but I can't work out how to convert Glyphs round robin
retrieval of the server endpoint into an async balancing decision in the
buildProtocol method of the Factory. If I return a deferred here it fails
with an AttributeError: Deferred instance has no attribute 'makeConnection'.
Currently I'm working around this by running a separate management loop
that periodically updates a dictionary with all the data necessary to make
my routing decision so that I can do it without a deferred. This worries me
because I may be making my decision on slightly stale data and I'd really
like this to be a real time decision as the connection comes in. Does
anyone have a clever way of doing this?
An example is below. The hashed out buildProtocol is a synchronous decision
which works. Thanks in advance!
from twisted.internet.protocol import Factory
from twisted.protocols.portforward import ProxyFactory
from twisted.internet import reactor, defer
import random
from twisted.python import log
import sys
log.startLogging(sys.stderr)
local_ports = set([1024, 1025])
def port_routing_decision_sync():
return random.choice(list(local_ports))
def port_routing_decision_async():
d = defer.Deferred()
reactor.callLater(1, d.callback, port_routing_decision_sync())
return d
class Balancer(Factory):
# def buildProtocol(self, addr):
# port = port_routing_decision_sync()
# print "connecting to local port {}".format(port)
# return ProxyFactory("127.0.0.1", port).buildProtocol(addr)
@defer.inlineCallbacks
def buildProtocol(self, addr):
port = yield port_routing_decision_async()
print "connecting to local port {}".format(port)
defer.returnValue(ProxyFactory("127.0.0.1",
port).buildProtocol(addr))
def main():
factory = Balancer()
reactor.listenTCP(5678, factory)
reactor.run()
if __name__ == "__main__":
main()
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