Add dockerfile generator

[kraih]

I want to be able to do

$ ./myapp.pl generate dockerfile

and

$ ./script/my_app generate dockerfile

to get a minimal but working Dockerfile for a Mojolicious app. It should probably start with an official perl container from Docker Hub, run cpanm --installdeps to install dependencies, and finally start the app in prefork mode. Nothing fancy, just enough to get started.

And of course there should be a new recipe in the Deployment section of the cookbook. Describing how to declare dependencies and also showing a minimal Dockerfile to build a container for a Mojolicious app.

[mohawk2]

Comment moved to graphql-perl/graphql-perl#29.

[kraih]

@mohawk2 I strongly disagree, getting it "right" (for whatever definition) from the start is not important at all. All we have to do is give our users a minimal starting point for their first experiments with containerization. Any complexity with multiple dockerfiles would be counter productive. More complex generators can be shipped as 3rd party modules on CPAN.

[zakame]

(Putting my docker-perl hat on...)

Yep, probably simplest is a ./script/myapp generate dockerfile that produces:

FROM perl:5.32
ADD . /app
WORKDIR /app
RUN cpanm Mojolicious && cpanm --installdeps .
EXPOSE 3000
CMD ["./script/myapp","prefork"]

There are a few assumptions like whether there's a cpanfile or Makefile.PL already around, what ports to use, etc. but I suppose these can be parameterized/templated (or just document calling script/myapp generate makefile prior.) Also probably worth noting (but not too important) is the base perl image to use; the regular variant is heavy but good for general development, but for documenting deployments it might be worth using a :slim variant...

[kraih]

The default port 3000 should be fine, no need to make everything configurable. I trust our users do edit a dockerfile if they have to. 😉 The generator should probably output a warning though if a Makefile.PL or cpanfile is missing. Caring about a :slim variant doesn't seem that important, maybe as a side note in the cookbook recipe.

[tianon]

Given it's generating in the context of a my_app / myapp.pl, do you think it makes sense to do things like WORKDIR /opt/my_app (instead of the generic /app) and/or pin cpanm Mojolicious to the particular version being currently used (like the makefile generator does)?

I would imagine if folks have a cpanfile or Makefile.PL that it already lists Mojolicious, so we probably should do one or the other of cpanm Mojolicious and cpanm --installdeps (not both) right?

FROM perl:5.32
RUN cpanm Mojolicious@8.64
WORKDIR /opt/my_app
COPY . .
EXPOSE 3000
CMD ["./script/my_app", "prefork"]

or:

FROM perl:5.32
WORKDIR /opt/my_app
COPY . .
RUN cpanm --installdeps .
EXPOSE 3000
CMD ["./script/my_app", "prefork"]

[tianon]

For the cookbook (to get folks thinking about how to improve their cacheability, etc), I would probably go slightly more complex with something like this, which would dovetail nicely with the makefile generator's output:

FROM perl:5.32
WORKDIR /opt/my_app
COPY Makefile.PL .
RUN cpanm --installdeps .
COPY . .
EXPOSE 3000
CMD ["./script/my_app", "prefork"]

(This makes sure the cpanm only reinstalls deps when Makefile.PL changes, although doesn't work in more complex cases like sourcing VERSION from another module, so isn't a sane default for the generator.)

[kraih]

@tianon The VERSION is hardcoded in the Makefile.PL created by ./myapp generate makefile though.

[tianon]

Right, so my thought is that this should either use cpanm Mojolicious@8.64 (matching the makefile generator) or should assume users use that makefile generator and instead use just cpanm --installdeps .

[tianon]

Do you think it makes sense to change the output depending on whether a Makefile.PL exists, or should we just assume that one does and/or throw a warning if it is missing?

What about for a Lite app - should the result copy just the single script or should it still be basically the same?

(Edit: I've pushed the very absolute basics to master...tianon:dockerfile, shamelessly copying from makefile.pm -- happy to make a PR or do more on it with some guidance but don't want to pester 😄 IMO it definitely needs to get clever with ->app to at least get the right app name in there 😇)

[kraih]

If you're creating a dockerfile for a lite app i think we should assume that there's more stuff to be copied in the directory (like templates and static files at least).

Edit: Yes, it should detect the right script to put into the dockerfile.

[tianon]

I've updated master...tianon:dockerfile with a bit more - I'd love some feedback (I'm admittedly a little bit over my own head, but trying to work it out 😅 ❤️).

One thing I'm not a huge fan of is that my $exe detection currently will turn mojo generate dockerfile into something like ../../../bin/mojo (for a system installed mojo binary), so I'm thinking it might make sense to add some detection there and convert anything that starts with ../ into script/$name instead?

I'm happy to adjust or even let someone else take over if I'm completely on the wrong track, but I'm also enjoying my attempt. 😄

[kraih]

@tianon That might just be the best we can do for script detection. Personally, i don't care too much about the mojo generate dockerfile case (it could just as well use ... if $self->app->isa('Mojo::HelloWorld') to set some static default). Or we could use $ENV{MOJO_EXE} || ('script/' . $self->app->moniker). There is no need to overthink it.

[tianon]

Totally fair, and makes sense -- folks who've renamed their script ought to know what they're getting into already. 😄

I've pushed the updated version to master...tianon:dockerfile -- do you think it's ready for a PR, or is there more I ought to put into this first?

[kraih]

Sure, there will be style change requests, but it seems enough to get the review process started.