Heroku CI: Support building rails 6 with multiple databases on multiple nodes

[adherr]

We have multiple postgres databases (in different clouds in production) that we want to test against with Heroku CI with multiple nodes.

• Our primary database is set to use heroku-postgresql:in-dyno which works fine.
• A second database is running as heroku-postgresql:standard-0, and during db:structure:load_if_sql in the buildpack, whichever node arrives first loads the structure, and all later nodes spew ERRORs about the structure already existing.
  • On occassion, two nodes attempt to apply migrations simultaneously, causing one of them to error out the build with a ActiveRecord::ConcurrentMigrationError 😞.
  • Even with transactional tests, we sometimes fail tests that count database records. This seems like a bug elsewhere, but being able to provision a second in-dyno database (another db in the same postgresql server even) would solve this problem.

[schneems]

Thanks for the issue, sorry for the delay. I don't have a fix for this or one planned, unfortunately.