[Glass] load balancer configuration

[Marten Felddtmann]

Hi,

this is a very interesting topic and actually I do not find any good 
solution under Apache (or perhaps nginx). I mentioned this in my talk at 
the London User Group last month regarding Gemstone/S. Apache (perhaps 
also nginx) do not have the knowledge to make the delivery of the http 
request in a good way to Gemstone.

I had more or less luck, that the modelling tool for Gemstone (I use) 
allows me to categorize the API (HTTP) calls into different categories: 
normal, long and memory and this works most of the time using the 
standard balancer of Apache. Its getting more complicated, when the 
usage of a server is getting higher and higher ... then there is 
theoretical a point, where the whole communication collapses (in a 
notable way of the end user: more and more UI errors a showing).

Even with these categories, implementing background tasks in Gemstone/S 
solutions seems to be a general suitable pattern (in the API oriented 
way) (so, the UI is defining a background task with parameters and then 
it is waiting for an event, that the work has been done).

The solution to this problem would be a total different way of delivery 
the http requests to Gemstone. Around 2012/15 there was an experimental 
http server mongel2 available, which works as a http-server and a zeromq 
backend. So the backend processes pull their next request (however pull 
is implemented). By using the available software it would be perhaps 
more useful to use the RabbitMQ library from Gemstone and write a mapper 
between http and rabbitmq.

As I mentioned above: I have a working solution, but not a good solution 
- but it works now for more than 8 years.

My Gemstone/S solutions are all API-oriented, sessions are persistent 
(so available in all processes), UI is written in JS .

Marten

On 20.12.23 13:04, Otto Behrens via Glass wrote:
> 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
>
> 	FINWorks
>
>
>
>
> FINWorks <http://za.linkedin.com/in/waltherbehrens> 	www.finworks.biz 
> <http://www.finworks.biz/>
>
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