Make the official Heroku buildpack for Node.js compatible with other buildpacks

The maximum allowed Heroku slug size (after compression) is 300MB. Image-heavy apps can somethings butt up against this limit, especially when using multiple buildpacks. If you're using Node.js to compile your front-end assets, but not to run your app, you may be able to save a large amount of space by deleting the node_modules directory before slug compilation.

There is currently an incompatibility between the Node.js and other buildpacks. On dyno boot, the nodejs.sh startup script sets the WEB_CONCURRENCY variable. The launch scripts of subsequent buildpacks will pick this us with no way of knowing that it wasn't set by a user.

First, set the Node.js buildpack to compile your assets:

$ heroku buildpacks:set heroku/nodejs

Next, add the Node Cleanup buildpack to get rid of the node_modules directory:

$ heroku buildpacks:set --index 1 https://github.com/istrategylabs/heroku-buildpack-node-cleanup

Finally, add whichever buildpack runs your app:

$ heroku buildpacks:set --index 2 heroku/python

For more general information about buildpacks on Heroku:

• Using Multiple Buildpacks for an App
• Slug Compiler