Heroku Buildpack: Crystal

This is an unofficial Heroku buildpack for Crystal apps, powered by shards, the dependency manager for Crystal.

There are no restrictions around what software can be used (as long as it can be compiled using shards build heroku). Web processes must bind to $PORT, and only the HTTP protocol is permitted for incoming connections.

In your shard.yml, you must specify a heroku target for this buildpack to build:

$ cat shard.yml
name: example-crystal
version: 0.1.0
authors:
  - Matthew Fisher <[email protected]>
targets:
  heroku:
    main: src/main.cr
crystal: 0.20.1
license: Apache-2.0

For an example application, see the example-crystal app.

See it in Action

Deploying a Crystal application couldn't be easier:

$ ls
LICENSE   README.md shard.yml src
$ heroku create --buildpack https://github.com/fishworks/heroku-buildpack-crystal
$ git push heroku master
...
-----> Crystal app detected
-----> Installing crystal-0.20.1
-----> Installing shards-0.7.1
-----> Running `shards build heroku`
       Building: heroku
-----> Discovering process types
       Procfile declares types -> (none)

A shard.yml file must be present at the root of your application's repository.

Crystal Versions

Specific versions of the Crystal runtime can be specified by setting the CRYSTAL_VERSION environment variable:

$ heroku config:set CRYSTAL_VERSION=0.20.1

Here is a list of supported Crystal versions:

• 0.8.*
• 0.9.*
• 0.10.*
• 0.11.*
• 0.12.*
• 0.13.*
• 0.14.*
• 0.15.*
• 0.16.*
• 0.17.*
• 0.18.*
• 0.19.*
• 0.20.*

You can also specify the shards version by setting SHARDS_VERSION, e.g.

$ heroku config:set SHARDS_VERSION=0.7.1

Testing

To test a change to this buildpack, write a unit test in tests/run that asserts your change and run make test to ensure the change works as intended and does not break backwards compatibility.