This buildpack has the following interface:

• A BUILD_SUBDIR Heroku config variable containing a relative path to the subdirectory of the app in the repo.
• A Bash script containing build commands, located at $BUILD_SUBDIR/heroku.sh.
• A manifest containing runtime commands, located at $BUILD_SUBDIR/Procfile.

In a monorepo, you might have multiple projects in subdirectories that each could be deployed to Heroku:

.
├── project1
└── project2
    ├── Procfile
    └── client
        └── package.json
    ├── heroku.sh
    └── server
        └── Gemfile

Set a config var to tell Heroku which subdirectory the project is in:

heroku config:add BUILD_SUBDIR="project2"

Add this buildpack:

heroku buildpacks:add https://github.com/croaky/heroku-buildpack-monorepo.git

Write a build script, project2/heroku.sh. See the React with Rails API example.

These Heroku Buildpack API environment variables are available to the heroku.sh script:

• BUILD_DIR
• CACHE_DIR
• ENV_DIR

Deploy:

git push heroku master
...
-----> Heroku receiving push
-----> Fetching custom buildpack
-----> Monorepo app detected