How to set ENV var in Heroku preview app postdeploy script - heroku

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.

Answer 2

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

Answer 3

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"

Answer 4

Using python requests within a postdeploy script:
import requests
result = requests.patch(f"https://api.heroku.com/apps/{os.environ.get('HEROKU_APP_NAME')}/config-vars",
data=json.dumps({"YOUR_KEY": "SOME_VALUE"}),
headers={"Content-Type": "application/json",
"Accept": "application/vnd.heroku+json; version=3",
"Authorization": f"Bearer {os.environ.get("HEROKU_API_KEY")}"}
)
Or using curl when logged:
curl -n -X PATCH https://api.heroku.com/apps/$HEROKU_APP_NAME/config-vars \
-d '{
"FOO": "bar",
"BAZ": "qux"
}' \
-H "Content-Type: application/json" \
-H "Accept: application/vnd.heroku+json; version=3"
And when not logged in add the header, where an app token has been generated:
-H "Authorization: Bearer $HEROKU_API_KEY"
https://2.python-requests.org/en/master/user/authentication/#netrc-authentication
https://devcenter.heroku.com/articles/platform-api-reference#curl-examples