Deploy Git subdirectory to Heroku

Here’s how you can deploy only your git subdirectory/subfolder to Heroku using git-subtrees 🌳.

The Situation

So why not just deploy the whole repo?

You might want to only deploy a subdirectory if the rest of the repo contains folders that are unrelated or unnecessary for your app to run. (Make sure that the subdirectory you’re building is truly independent first!)

Or in my case, you might need to only deploy the subdirectory because the repository might not be something you can actually build:

remote: Building source:
remote:
remote:  !     No default language could be detected for this app.
remote:    HINT: This occurs when Heroku cannot detect the buildpack to use for this application automatically.
remote:    See https://devcenter.heroku.com/articles/buildpacks
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: ! Push rejected to app-name.
remote:
To https://git.heroku.com/app-name.git

Feels bad to be rejected…

I even tried to tell Heroku which default language to use:

heroku buildpacks:set heroku/nodejs

For Node.js specifically, this means that Heroku couldn’t find a package.json:

remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> App not compatible with buildpack: https://codon-buildpacks.s3.amazonaws.com/buildpacks/heroku/nodejs.tgz
remote:        Node.js: package.json not found in application root
remote:
remote:        More info: https://devcenter.heroku.com/articles/buildpacks#detection-failure
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: ! Push rejected to my-app.
remote:
To https://git.heroku.com/my-app.git

The Solution

Probably what you’re here for

Heroku Setup

npm install -g heroku
heroku login
heroku git:remote -a my-app

🌳 Git-subtree 🌳

Make sure to run this from the top level of the tree:

git subtree push --prefix path/to/subdirectory heroku master

For example, if the subdirectory I want to deploy my-app is in the root my-repo, then I run:

git subtree push --prefix my-app heroku master

And then…

remote: Building source:
remote:
remote: -----> Node.js app detected
...
remote: Verifying deploy... done.
To https://git.heroku.com/my-app.git

🎉🎉 Beautiful 🎉🎉

Other Resources

• https://stackoverflow.com/questions/7539382/how-can-i-deploy-push-only-a-subdirectory-of-my-git-repo-to-heroku
• https://coderwall.com/p/ssxp5q/heroku-deployment-without-the-app-being-at-the-repo-root-in-a-subfolder
• https://www.atlassian.com/blog/git/alternatives-to-git-submodule-git-subtree
• https://medium.com/@porteneuve/mastering-git-subtrees-943d29a798ec