Common Lisp on Heroku -- Example Project

This project is an example of how to deploy a common lisp server to heroku using docker.

Instructions:

Fork or clone this project (and optionally modify it with your own content).

Get yourself set up with a Heroku account and tools.

Install heroku's command line interface.

Make sure you're logged in with heroku:

$ heroku login

Then log into heroku's docker registry:

$ heroku container:login

Create your own Heroku application:

$ heroku create

Then you can push the docker image to heroku's repository (the docker image will be built locally):

$ heroku container:push --recursive

You can then release the docker image:

$ heroku container:release web

Finally, you call open the application:

$ heroku app:open

That's it!

The docker image is based on ubuntu (latest), it has multiple stages to try to shorten the build time.

Stage basepackages contains the OS and a few packages (like sbcl) needed at build- and run-time.
Stage quicklisp install and configure quicklisp. Notably, it also installs ironclad because it's a package that takes a while to compile.
Stage dependencies is the first stage that depends on the application's code. It uses only 2 files from the context (the directory from which docker copies the files). It uses the file example.asd to know what are the (quicklisp) dependencies of the application. And it uses compile-dependencies.lisp to build an image (dependencies.core) that contains all the application's dependencies.
Stage build copies all the source files, load dependencies.core and load the (common lisp) system example and create an executable called lispapp. The entry-point of the executable is the function example:start.

It would be possible to improve the size of the docker image by including only the lispapp executable in an extra stage at the end.