Add uWSGI application server

[abbradar]

For now only Python plugins are supported (I haven't used uwsgi for anything besides Python and have no idea of needed workarounds, environs and so on).

[domenkozar]

We should probably support running more than one instance of uwsgi

[abbradar]

Good idea. This should look better together with systemd's @-services, but I can't find any examples of starting several instances of it. Specifically, after defining systemd.services."uwsgi@", how do I start uwsgi@abc and uwsgi@def (given I have [ "abc" "def" ])? AFAIU, adding systemd.services."uwsgi@abc" would make a completely new service instead of using uwsgi@.

[prikhi]

Have you looked into uwsgi's emperor mode:
http://uwsgi-docs.readthedocs.org/en/latest/Emperor.html

This just requires starting the uwsgi in --emperor mode and adding configurations or symlinks to a directory.

Let me know if I can help out in any way.

[abbradar]

The emperor mode would already work with this, but multiple uwsgi instances would be simpler for end-user if they are statically known.
Unfortunately I have too many things to do now, so I've decided to resume work on this after New Year.

[abbradar]

I've thought about this -- emperor mode and multiple systemd services implement the same thing, if one would describe everything in his configuration. If not, emperor mode can be more flexible, as we can state a directory and add or remove services from it. If emperor mode would be enough for everyone, we can leave this as a single systemd service -- are there any usecases where multiple services would be better?

[prikhi]

I use emporer mode whenever I need more than 1 uwsgi instance, but I only use it for python/django so I'm not sure about other scenarios.

[abbradar]

So, @iElectric , do we need to support more than one instance or emperor mode should be enough? Maybe with some additional support from the module side?

[domenkozar]

We could use emperor mode in NixOS itself, but I'd still have configuration for multiple services as a module.

[domenkozar]

@abbradar we could touch that later, if you feel it's too much work.

[abbradar]

Sorry for taking a long time, redone this -- now you can have arbitrary tree of emperors and their vassals with some sugar for configuration.
@iElectric That wasn't the problem, rather I was busy with a lot of other things ^_^

[matthiasbeyer]

new-package label missing.

[matthiasbeyer]

The indention of this line is more than of the other lines. Is there any reason for this?

Sorry for bitching around because of this, but this stuff makes reviewing hard, at least for me... 😏

[abbradar]

This is codestyle oftenly used in Haskell, sorry for this. I'll fix this to stick to Nix standards.

[prikhi]

So the "pure" way to use this with python would be to create a custom package for the project you're deploying and feed this to normal mode?

[abbradar]

@prikhi Sorry for taking a long to answer. No, you are supposed to set python2Packages or python3Packages (depends on what you want) to a function which takes a set with packages and returns a list with needed ones.

[abbradar]

@matthiasbeyer I tried to make it look better, try this and please say what I can improve. And thanks for the criticism, in my opinion it is very important for the code to be structured as readable as possible!

[domenkozar]

Might be a good idea to add an example configuration to documentation.

[abbradar]

Added example and fixed a couple of bugs while at it; now emperor mode is properly tested, too.

[abbradar]

Any further comments? I think of merging this tomorrow.

[prikhi]

I don't understand the significance of having python2/3Packages be a function instead of a list, but my nix-fu is not too superb.

[abbradar]

This is to enforce you to use Python packages of the same version as Python uWSGI was compiled with. Well, it's not enforcing you in reality (you can as well return your own evil package), but this way you wouldn't bother about version mismatches -- if uWSGI's Python changes, so will input to your function, and hence, versions of your packages.

[abbradar]

You can look at it as a way for you to write

python2Packages = args: with args; [ pkg1 pkg2 ];

instead of

python2Packages =
  let args = pkgs.python2Packages.override {
    python = pkgs.uwsgi.python2;
    self = args;
  };
  in with args; [ pkg1 pkg2 ];

or (unsafe! we don't know if uwsgi was built with the same Python as default!)

python2Packages = with pkgs.python2Packages; [ pkg1 pkg2 ];

[domenkozar]