[Glass] load balancer configuration

[Otto Behrens]

Hi,

We are using nginx to load balance in front of GemStone that runs a Seaside
application. Some of our requests run too long (we are working hard to cut
them down) and in general, the time it takes to service a request in our
application varies between 0.1 and about 4 seconds. We are improving and
getting more towards the lower end of that.

Because of this, we use the least_conn directive and we persist session
state so that we could use any of our GemStone upstream sessions to service
a request. Requests are generally load balanced to idle sessions and there
are theoretically no requests that wait for another to get serviced.
Perhaps this is not optimal and you have better suggestions. It has worked
ok for a long time, but should we consider another approach?

When our code misbehaves and a request takes let's say 60 seconds to
handle, things go pear shaped (yes we want to eliminate them). The user
clicks "back" on the browser or closes the browser and nginx picks it up
with:
"epoll_wait() reported that client prematurely closed connection, so
upstream connection is closed too while sending request to upstream"

We suspect our problem is: when this happens, it appears as if nginx then
routes requests to that same upstream, which is unable to handle it because
it is busy handling the previous request (which is taking too long), even
with some upstream sessions sitting idle. Some users then end up with no
response.

Ideally, we would like to catch the situation in the GemStone session and
stop processing the request (when nginx closes the upstream connection).
Alternatively, we could set timeouts long enough so that if the browser
prematurely closes the connection, nginx does not close the upstream
connection.

Do you have a suggestion to handle this? Does it make sense to get timeouts
(which ones?) to align so that this does not happen?

Thanks a lot

Otto Behrens

+27 82 809 2375
[image: FINWorks]
[image: FINWorks] <http://za.linkedin.com/in/waltherbehrens>
www.finworks.biz

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