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Hi,
From the implementation viewpoint, Windows Load Balancing Service
implements a local filter between the NIC driver and the TCP/IP stack.
There is a filtering function, which can map incoming packets to the
cluster ndoe based on the source IP address and port number and only
pass the packets to the upper layer in one node. If some nodes fails or
new nodes are added, all the cluster nodes need neogociate a new
filtering function. I guess that each node may keep states of its
established connections, so that even under a new filtering function,
the packets destined for the local node can still be passed to the upper
layer, the new filtering function only works on new connections (SYN
packets). However, in persistent services, the new filtering function
will make all the persistence broken, no matter that they are connected
to the alive nodes or the failed nodes. It affects all the nodes. I see
that's the big shortcoming, but the distributed fileter architecture can
avoid the failure of dispatcher.
It is simple to write a filter, but it must be complicated to write
convergence stuff (negociation for a new function).
I see that maybe we can learn somethings from it, investigate some
mechanism to implement active-active load balancers.
Cheers,
Wensong
On Thu, 4 Jan 2001, ratz wrote:
>
> Finally someone comes up with it. I didn't dare to mention it but
> you might have a look at:
>
> http://www.microsoft.com/TechNet/win2000/nlbovw.asp?a=printable
>
> This really is the first text I read from Microsoft that impressed
> me quite a bit. They have some very advanced approach to clustering
> and loadbalancing. For example (for those that don't want to read it):
>
> o They have a slightely different architectural approach to LVS-DR.
> It looks very promising and I'd love to test it out but I can't
> since I don't have a copy of W2K.
> o They claim to have a real cluster with fully distributed software
> architecture.
> o Because of the different design architecture they can achieve very
> statistical load balanced services even with sticky option. Example:
> "When inspecting an arriving packet, all hosts simultaneously perform
> a statistical mapping to quickly determine which host should handle
> the packet. The mapping uses a randomization function that calculates
> a host priority based on the client's IP address, port, and other state
> information maintained to optimize load balance. The corresponding
> host forwards the packet up the network stack to TCP/IP, and the other
> cluster hosts discard it."
> o They have some kind of SSL Termination and persistent cookie support.
> o Interesting arguments such as:" This architecture maximizes throughput
> by using the broadcast subnet to deliver incoming network traffic to
> all cluster hosts and by eliminating the need to route incoming
> packets to individual cluster hosts. Since filtering unwanted packets
> is faster than routing packets (which involves receiving, examining,
> rewriting, and resending), Network Load Balancing delivers higher
> network throughput than dispatcher-based solutions. As network and
> server speeds grow, its throughput also grows proportionally, thus
> eliminating any dependency on a particular hardware routing implementation.
> For example, Network Load Balancing has demonstrated 250 megabits per
> second (Mbps) throughput on Gigabit networks."
> o they have PPC, persistency mask, different schedulers, failover,
> healthcheck, state transition table synchronisation (see Convergence),
> LVS-DR (somehow described under "Distribution of Cluster Traffic #1"),
> event-logging, special ether type-value [0x886F], simple filtering.
> o Oh, I forget to tell you that you can only go up to 32 servers :)
>
> But hey, maybe he doesn't have a W2K farm :)
> To finalize and come back to your initial question: Doesn't W2K have
> something like a MS loopback adapter? In the paper above they mentioned
> something like this (cluster adapter)
>
> Best regards,
> Roberto Nibali, ratz
>
> --
> mailto: `echo NrOatSz@xxxxxxxxx | sed 's/[NOSPAM]//g'`
>
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