First problem I ran into was Heroku complaining that it couldn't install sqlite3. Now this is a well-documented problem which requires that you make sure that your sqlite gem is only available in test and development but not in production as Heroku no longer supports that. It's a simple fix:
gem sqlite3, :group => [:development, :test]
I dutifully made the change and pushed to my test app but it continued to fail. After an embarrasingly long time, I remembered that I was working on branch 'cedar' (isolating these changes) but the push was going to 'master'. This was a quick fix:
git push test-app HEAD:master
pushes the current HEAD to master on Heroku... problem solved.
Then I ran into a further complication; Bundler worked fine but the Heroku assets:procompile was failing with
could not connect to server: Connection refused Is the server running on host "127.0.0.1" and accepting TCP/IP connections on port xxxx?
This was a simple solution, found in the previous reference in the 'Troubleshooting' section; just add this to my application.rb file:
config.assets.initialize_on_precompile = falseNow I could run my migrations, install the sendgrid addon, and my test-app was up and running. Hopefully this can save someone a bit of time.