How to set ENV var in Heroku preview app postdeploy script

Question

I want to set the HOST env var to $HEROKU_APP_NAME.herokuapps.com on a preview app. It doesn't look like I can do this in app.json since this is a computed value.

I was hoping to do it in a "postdeploy" script like this

heroku config:set HOST="`heroku config:get HEROKU_APP_NAME -a neon-dev-pr-520`.herokuapps.com"

but it wants to authenticate me as a Heroku user. Alas, this doesn't work either:

export HOST=$HEROKU_APP_NAME.herokuapps.com

Any suggestions?

Answer 1

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 bash

echo $HEROKU_APP_NAME
export SERVER_URL=https://$HEROKU_APP_NAME.herokuapp.com/parse

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