On 11/23/2018 4:38 PM, Philip McGrath wrote:
I'm not familiar with Ruby, so this is just some general information.
The Racket web server already supports concurrency with its built-in
green threads, so handling one request won't block the concurrent
handling of another. (Not all languages' built-in web servers do this;
I don't know about Ruby in particular).
There isn't built-in support for parallelism, i.e. for taking
advantage of multiple processor cores. This isn't built in, and I
don't personally need this (my server only has two cores, and it runs
a database and other processes in addition to Racket). However, it is
probably possible to recreate the architecture you describe.
Essentially you would be running multiple instances of your
application behind a load-balancer. If you want to use nginx as a load
balancer, that's out of the equation; implementing a load-balancer in
Racket would certainly be possible but probably more work.
Extra-linguistically, you could just create a few systemd services or
similar to run several totally separate Racket instances. Within
Racket, you would want to build on "places." You can have N worker
places running N instances of your application on N OS-level threads,
plus a master place to control them. A mechanism for gracefully
stopping the Racket web server is built in (see serve/launch/wait
<https://docs.racket-lang.org/web-server-internal/web-server.html#(def._((lib._web-server%2Fservlet-dispatch..rkt)._serve%2Flaunch%2Fwait))>).
Reloading isn't built in, but I've heard good things about the
"reloadable" package
(https://pkgs.racket-lang.org/package/reloadable), which should let
you implement it if needed.
While I only run one instance of our application, I do use places to
redirect HTTP to HTTPS.
One caveat is that all of this assumes that, if you are using
continuations at all, you are using serializable continuations with
`#lang web-server`. Making places work well with native continuations
would probably be a lot of work, and it would probably be better to
build that functionality into the Racket web server than to try to
fake it as a client.
-Philip
Just a comment:
Multiple (identical) server instances running on the same machine can
listen for connections on the same network port - an incoming client
call will be connected to only one of them. You only need to use
different ports when services are not interchangeable [i.e. it matters
which one you are talking to].
Process parallelism, in effect, can give you automatic connection load
balancing on a single machine. Using a separate load balancer in front
technically is overkill for such situations, but it is a good design if
you want to preserve the option to relocate your services to different
machines.
George
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