[racket] Web server

Jay:

Can you clarify your statement, "Session affinity doesn't really make a lot of sense in the continuation context, fwiw." ?

I haven't really dug into the web server yet, so I may simply be misunderstanding how it works, but at least in the case of stateful continuations, I thought it was important for all of a user's subsequent requests to go to the same process that served the first request since there would be state stored in the memory of the web server process. 

Is that not the case? Or are all continuations serialized to disk so that any Racket web server process (assuming there are multiple instances running) could serve a subsequent request for any continuation?

To be clear, the scenario I'm envisioning is that of an nginx web server handling all incoming http requests, serving static files itself and proxying all other requests to a set of Racket web server instances using some sort of load balancing such as round robin. I assumed that if I begin my session with process-1 and then the next request was served by process-2, it would fail.

Thanks,
Brian

On Jul 16, 2014, at 10:17 PM, Jay McCarthy wrote:

> It wouldn't have a big impact on the server. The big question is how
> to effectively use multi-core in Racket programs generally.
> 
> Futures are really only good for numerical codes that stay in the JIT,
> which doesn't sound like most Web programs. That said, it is trivial
> to implement:
> 
> #lang racket/base
> (require racket/future
>         web-server/servlet-env
>         web-server/http)
> 
> (define (fib n)
>  (if (< n 2)
>    1
>    (+ (fib (- n 1))
>       (fib (- n 2)))))
> 
> (define (start req)
>  (touch
>   (future
>    (λ ()
>      (response/xexpr
>       `(html
>         (body
>          (p "It's "
>             ,(number->string
>               (fib (random 20)))))))))))
> 
> (serve/servlet start)
> 
> Boom! That's a servlet that uses multi-core to handle every request...
> of course, it probably doesn't pay in this or most other programs.
> 
> Places are for more coarse-grained things and you can pass file
> descriptors, so it's feasible to have a TCP accepter that feeds work
> to a group of places servicing the requests. However, places must not
> use mutation to communicate higher-order values (they can communicate
> flat values like numbers with mutation), so they couldn't share
> continuations. It would be trivial to use serializable continuations
> or to implement a continuation manager that stored all the
> continuations in a single place. Session affinity doesn't really make
> a lot of sense in the continuation context, fwiw.
> 
> My guess is that you could spend less than 100 lines to implement the
> continuation manager and the place-based worker setup. (This is based
> on the normal server setup just being 127 lines and the manager
> interface being implemented in as little as 40 lines.) This might be
> worth it.
> 
> Jay
> 
> 
> On Wed, Jul 16, 2014 at 4:09 PM, Brian Adkins <racketusers at lojic.com> wrote:
>> I haven't looked into the Racket web server much yet, so I'd like to understand the implications of this.
>> 
>> My experience is with stateless http app servers (primarily with Unicorn Ruby servers at the moment), so firing up a number of worker processes and having something like nginx proxy to them works well to fully utilize all cores.
>> 
>> I think I read that the Racket web server makes use of continuations, so I expect some sort of process affinity would be necessary, where a given user's requests are always proxied to the same worker process - is that right? Is it common to use multiple web server processes in Racket web apps?
>> 
>> In your estimation, what is the feasibility of adding multi-core support to the Racket web server? For example, is it reasonably feasible and on the current roadmap, or would it require massive changes to the web server?
>> 
>> Thanks,
>> Brian
>> 
>> On Jul 16, 2014, at 8:42 AM, Jay McCarthy wrote:
>> 
>>> It does not use multiple cores if they are available.
>>> 
>>> Jay
>>> 
>>> On Wed, Jul 16, 2014 at 7:02 AM, Sean Kemplay <sean.kemplay at gmail.com> wrote:
>>>> Hello,
>>>> 
>>>> I am interested in the racket web server for some micro services. Just
>>>> wondering if by default it runs across multiple cores or if it is restricted
>>>> to one due to threads in racket.
>>>> 
>>>> Regards,
>>>> Sean
>>>> 
>>>> 
>>>> ____________________
>>>> Racket Users list:
>>>> http://lists.racket-lang.org/users
>>>> 
>>> 
>>> 
>>> 
>>> --
>>> Jay McCarthy
>>> http://jeapostrophe.github.io
>>> 
>>>          "Wherefore, be not weary in well-doing,
>>>     for ye are laying the foundation of a great work.
>>> And out of small things proceedeth that which is great."
>>>                         - D&C 64:33
>>> ____________________
>>> Racket Users list:
>>> http://lists.racket-lang.org/users
>> 
> 
> 
> 
> -- 
> Jay McCarthy
> http://jeapostrophe.github.io
> 
>           "Wherefore, be not weary in well-doing,
>      for ye are laying the foundation of a great work.
> And out of small things proceedeth that which is great."
>                          - D&C 64:33