Why changing heroku buildpack for existing app doesn't run bin/release

Question

I had a php app on heroku with the default buildpack (apache), and then decided to change it to the php-fpm + nginx buildpack (https://github.com/iphoting/heroku-buildpack-php-tyler/).

I issued the change command:

heroku config:set BUILDPACK_URL=https://github.com/iphoting/heroku-buildpack-php-tyler.git

And pushed with:

git push heroku master

The slug then compiles, but all the binaries fail to execute with "command not found", because PATH config variable which should be updated with bin/release isn't updated.

In comparison, when creating an app from scratch with this buildpack with

heroku create -b https://github.com/iphoting/heroku-buildpack-php-tyler.git

Everything runs as expected (and PATH is present and updated).

My assumption is that bin/release was not run after changing the config variable BUILDPACK_URL, and therefore the PATH variable isn't set.

In order to make the app work, I had to manually add the PATH config variable. Did anybody else ever encounter this? Is this the expected behavior? By my understanding, bin/release should always run after a slug compile?

EDIT: corrected the git url to the correct ".git" one

Answer 1

You are correct in your assumption, the addons and config_vars properties of bin/release are only taken from a buildpack on an app's first deploy. See https://devcenter.heroku.com/articles/buildpack-api#binrelease for more details.

Heroku is moving over to a new system for a buildpack to add config vars that will work beyond an app's first deploy: https://devcenter.heroku.com/articles/labs-dot-profile-d

If a buildpack copies a .profile.d/buildpack_name.sh into the app, that file will be sourced during application boot. This can be used to set up things like the PATH.

Answer 2

You probably have a Procfile in your app repository. If you have an existing Procfile, then bin/release won't overwrite its contents. Simply copy the appropriate lines (5-9) from https://github.com/iphoting/heroku-buildpack-php-tyler/blob/master/bin/release into your Procfile.