How to set ENV var in Heroku preview app postdeploy script

Worked out with the assistance of Heroku's awesome support team a few years ago. We needed to set a reflexive environment variable for a middleware (parse-server) to know what to connect to. It's set manually on our Staging and Production apps, but to get it set on our review apps:

My app.json incldues:

  "scripts": {    "postdeploy": "bin/bootstrap"  },...  "env": {    "HEROKU_APP_NAME": {      "required": true    },    "HEROKU_PARENT_APP_NAME": {      "required": true    },...

bin/bootstrap is:

#!/usr/bin/env bashecho $HEROKU_APP_NAMEexport SERVER_URL=https://$HEROKU_APP_NAME.herokuapp.com/parse

SERVER_URL is available (and correct) in my review apps. It's been 👍no problems since we implemented.

I found this post which suggests that you can use the Heroku PlatformAPI.

In this case as a Rails Rake task which is run as the postdeploy:

desc 'Bootstrap review app'task bootstrap: ['db:schema:load', 'db:seed'] do  heroku = PlatformAPI.connect_oauth(ENV['HEROKU_API_TOKEN'])  heroku.config_var.update(ENV['HEROKU_APP_NAME'], 'WWW_HOSTNAME' => "#{ENV['HEROKU_APP_NAME']}.herokuapp.com")end

Take a look at the documentation for review apps https://devcenter.heroku.com/articles/github-integration-review-apps#heroku_app_name-and-heroku_parent_app_name

As long as you declare HEROKU_APP_NAME or HEROKU_PARENT_APP_NAME as required or optional in your app.json file, they will be available for you to use in your postdeploy script so you can just do:

HOST="$HEROKU_APP_NAME.herokuapp.com"