Why do people believe the FlatManager is a bad option for networking?
Can someone explain why FlatManager is a bad networking option? In discussions of OpenStack's networking options, it is usually dismissed out of hand, but I can't find a good justification.
FlatManager has several advantages: no nova-network SPOF or overhead, easier to integrate with existing networks; and simplicity. I've had great experiences using FlatManager at small scale (apart from that it sometimes feels like I'm the only user!)
I presume there are disadvantages that outweigh the advantages, but I can't find what those are!
Let's ignore the lack of support for floating IPs: they will probably still need a nova-network service; right now nova-network isn't enabled with FlatManager; but I believe that it could be enabled with FlatManager and handle only floating-ip traffic. (Unless of course floating IPs + FlatManager is actually impossible!)
are you sure nova-network is not used with FlatManager? - I thought FlatManager was a class for nova-network to use.
darragh-oreilly: I'm pretty sure it doesn't need to be used (the FlatManager class seems to be used in both the compute node and nova-network). I've used a normal network gateway in the past, instead of nova-network. (I think you'd need nova-network for floating-ips, unless you played ARP tricks)
@justinsb: what do you mean by "nova-network"? I'm talking about the Python process that uses the class set by network_manager in nova.conf.
@darragh-oreilly: Looks like you're right (I re-read the code). I guess I'm asking why nova-network is in the path for outgoing network connections from a VM, vs just using the network's existing router (which presumably is just as capable of doing NAT).
@justinsb: ok - I see. So a downside of doing so much of the networking outside of OpenStack is that you are left with the task of somehow automating it along side OpenStack - or worse, doing it manually.