[Dancer-users] using Starman for powering dancer apps

[Naveed Massjouni]

On Mon, Jul 4, 2011 at 3:55 AM, Pedro Melo <melo at simplicidade.org> wrote:
> Hi,
>
> On Sun, Jul 3, 2011 at 11:59 PM, Mr. Puneet Kishor <punk.kish at gmail.com> wrote:
>
>> Ok, then I added another app "bar" under ~/Documents/www (sibling to "foo"). Now, I am trying to run multiple apps as per the instructions at [http://search.cpan.org/~sukria/Dancer-1.3060/lib/Dancer/Deployment.pod] under the heading "Running multiple apps with Plack::Builder".
>
> There was a thread one or two weeks back discussing this point. I
> didn't pay much attention to it, but I think the result was that the
> current instructions are wrong and a new version was committed to the
> git repo for the next release. Check the ML archives.
>
>> I created the following web.psgi file in ~/bin
>>
>> ----
> [...]
>>
>> builder {
>>        mount "/foo" => builder {$app1};
>>        mount "/bar" => builder {$app2};
>> };
>> ----
>
> <aside>
> Running multiple Dancer apps in the same process can be done, but I've
> always found it to be awkward.
>
> Its a design thing. Dancer uses a lot of global variables to do its
> magic so you need to keep switching the global context, including the
> configuration, per request. Its a tradeoff: you get a very cool and
> simple DSL to manipulate your request and response, but this requires
> a global context.
>
> For the same reason, its practically impossible to use Dancer with
> Twiggy and do long polling, where each perl interpreter will have
> multiple requests going at the same time.
>
> I don't see this as bugs or limitations, on the contrary. They are
> design tradeoffs, where you get a very very practical DSL but loose
> the possibility to do some things. I like that Dancer is willing to
> loose some features in order to be excellent at the rest. Not many
> frameworks are willing to do that, and the Dancer developers should be
> commended by this.
> </aside>
>
> If you are using a frontend reverse proxy (apache in your case), then
> my suggestion is that you start two starman instances with plackup,
> one for foo app and another for bar app, on different ports, and
> configure apache to do the proper url mapping to each one.
>
> Its simpler, IMHO more robust, and you can start/stop/restart each app
> separately, and tune the number of workers per app.
>
> I reverse setting up multiple apps in the same perl interpreter for
> very extreme cases, and I don't recommend it as a general solution.
>
>> Two, are both "foo" and "bar" going to be accessible at http://127.0.0.1:5001/? Do I just add the following lines to my httpd.conf
>>
>> ----
>> ProxyPass        /foo http://127.0.0.1:5001
>> ProxyPassReverse /foo http://127.0.0.1:5001
>> ProxyPass        /bar http://127.0.0.1:5001
>> ProxyPassReverse /bar http://127.0.0.1:5001
>> ----
>
> If you follow my suggestion above, tweek the second pair of lines to use 5002.
>
>
>> Three, how do I run plackup in the background? I want to run it, but be able to close the shell, and even logout and have it running.
>
> nohup plackup_cmd_line &
>
> is the usual way to do this, but plackup has a better way:
>
>    -D, --daemonize
>        Makes the process go background. It's up to the backend
>        server/handler implementation whether this option is respected or
>        not.
>
>
>> Four, if I have a single web.psgi as above, one disadvantage is that if I tinker with any one app, and have to turn off or restart Starman, it will affect all the apps powered by Starman. Perhaps a better situation would be to have a separate Starman process for each app. What is the best practice here?
>
> One plackup per app is my recommended approach as I wrote above. My
> modesty prevents me from calling this a "best practice" :)
>
> Bye,
> --
> Pedro Melo

Pedro, I think your explanation was excellent about the tradeoff that
Dancer makes. After reading this, I believe that the section in
Dancer::Deployment pod on deploying multiple apps should contain a
caveat. Something to the effect of, "Here is how you can deploy
multiple apps, but this is not the way Dancer is meant to be used.
Instead, consider multiple plackup processes."

-Naveed