Once again Gena you missed my point by a landslide. WRT/DSL were to show
proof it could be done and very low end hardware, you could always get
better hardware. Furthermore you fail-over logic is flawed, if done proper
you can prevent the failure pages to the end user. However the point was
not what the best solution in a case would be but the overall viability
.. I was simply shows a very basic approach improvements could be made.

You thought process of expecting it to be a fully planned out system, is
asking Alexander Gram-Bell how a cell phone tower would work, not could
it be possible in the future to have phones without wires, if such a
technology could be made?


However I digress this topic is dead at this point the user has been shown
several different ways where using nginx vs a hardware platform could be
done. Its not his job to plan and test it for his needs. Theory over
practice and all that.


-----Original Message-----
From: owner-nginx@sysoev.ru [mailto:owner-nginx@sysoev.ru] On Behalf Of Gena
Makhomed
Sent: Monday, September 21, 2009 5:50 AM
To: David Murphy
Subject: Re: Viability of nginx instead of hardware load balancer?

On Thursday, September 17, 2009 at 17:05:28, David Murphy wrote:

DM> If your load balancer is not doing anything but being a load
DM> balancer really you only needs high quality network devices, a
DM> minimalistic kernel (to prevent security holes) and ram based os or fast
HD.

WRT-54G has very limited amount of memory - 8 MB, 16MB or 32MB.
this is not proper hardware for high traffic http load balancer, you can
test it independently if not believe my humble opinion.

DM> I would agree you need better hardware if you are doing more but as
DM> a pure LB, hardware requirements and not a strict as you are implying.

even pure http LB need a quite lot of RAM for tcp buffers and states of
connections.

DM> Furthermore you need to get past this concept of "failures" because
DM> if you configured things properly you would have a hot spare device
DM> to prevent any such lag. I find that buying a single piece of
DM> hardware vs building out a redundant infrastructure a) costs more
DM> money and b) actually have a higher chance of failure due to a
DM> Single Point of Failure

lags/overloads - because of low performance of very cheap hardware (slow
CPU/not enough RAM).

failures - because of low reliability of very cheap hardware (obsolete
equipment).

DM> Also you have the ability via networking to run a true balanced
DM> share out of the load so you could have 3 LB's all getting one
DM> 1/3 of all requests and hitting the same backends. Then if one
DM> drops off the switch just downs the port and 1/2 goes to each of the
remaining LB nodes.

in case of persistent failure - yes, one drops off all active tcp
connections at that moment and go down.

even persistent failure dont have zero cost - it generates temporary denial
of service for all clients of these connections.

but, for exampe, in case of broken memory chips - failed LB not go down, and
continue to "work", generating broken ip packets or reboots/kernel panics.

DM> Your belief you must buy hardware is just a waste of capital
DM> investment, when you can build it yourself for much cheaper with
DM> the same of better hardware than buying something from a vendor.

I belief what WRT-54G is not appropriate hardware for load balancer and DSL
(2.4 kernel) DSL-N (development version) is not appropriate base OS for load
balancer, even if using high quality nginx server.

I belief need to be minimized not cost of some piece of hardware, but
minimize TCO of solution, if all QoS requirements satisfacted and scaling of
any part of system provided.

--
Best regards,
Gena