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Horms wrote:
On Wed, Nov 22, 2006 at 04:21:17PM +0100, Roberto Nibali wrote:
I personally believe that the sorry-server feature is a big missing
piece of framework in IPVS, one that is implemented in all commercial
HW load balancers.
That is true, but its also a piece that is trivially inplemented in
user-space, where higher-level monitoring is usually taking place anyway.
Is there a strong argument for having it in the kernel?
Yes, it won't work reliably in user space because of missing atomicity.
From the point the user space daemon decides that it's time to switch
over to the sorry-server pool to the actual switch in the kernel by
modifying the according service flag, there's a couple of us to ms time
frame in which the kernel TCP stack will happily proceed with its normal
tasks, including service more requests to the previously elected service
for sorry-server forwarding. This can lead to broken (half-shown) page
views an the customer's side inside their browser.
In the field I had to implement load balancing, this was simply not
accepted, especially because it irritated our customer's clients and
also because everybody knew that HW load balancers do it right (tm).
YMMV and I still didn't sit down and forward port my code to 2.6 but I
first need some interest by enough people before I start :).
Cheers,
Roberto Nibali, ratz
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