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Read a json ENV variable into a file for Heroku

Create a tmp-file to read from on Heroku together with google cloud

heroku google-cloud rails

While getting my transcription app on Heroku the credentials needed to get google cloud storage working spit out an error.

I forgot that the credentials are read in from a json file and just added them as a single ENV variable in Heroku.

Do so by going to your dashboard, navigate to your application and choose settings. Reveal config vars. Add the correct key (in this case that’s SPEECH_CREDENTIALS). Paste in the contents of the json file provided by google cloud.

The storage actually expects to read the credentials from a json file. I managed to get this working by creating an initializer config/initializers/google_cloud_credentials.rb and in there create a tmp file which the storage setup can read from.

  f ="tmp/transcribe.json", "w")
  service: GCS
  project: transcriber
  credentials: <%= Rails.root.join("tmp/transcriber.json") %>
  bucket: ENV["bucket"]

Important note

This creates an actual file in the tmp directory of your application. That means that if you allow (for some reason) users to read from there they can grab your credentials. Otherwise these credentials are only accessible by your and your system, just like the regular ENV variables.

I’m not sure if this is the best and easiest way to read in credentials from a json file but I kind of like the setup myself. If you have any other suggestions shoot me up over at

Written on September 1, 2020